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  • Polymer and Materials Science  (7,542)
  • Humans
  • 1990-1994  (8,415)
  • 1985-1989
  • 1991  (4,012)
  • 1990  (4,403)
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  • 1990-1994  (8,415)
  • 1985-1989
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 33 (1991), S. 442-449 
    ISSN: 1432-1432
    Keywords: Humans ; Mouse ; Rat ; Codon usage ; Mutation bias ; Selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A new statistical test has been developed to detect selection on silent sites. This test compares the codon usage within a gene and thus does not require knowledge of which genes are under the greatest selection, that there exist common trends in codon usage across genes, or that genes have the same mutation pattern. It also controls for mutational biases that might be introduced by the adjacent bases. The test was applied to 62 mammalian sequences, the significant codon usage biases were detected in all three species examined (humans, rats, and mice). However, these biases appear not to be the consequence of selection, but of the first base pair in the codon influencing the mutation pattern at the third position.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    International journal of biometeorology 34 (1990), S. 42-48 
    ISSN: 1432-1254
    Keywords: Briths ; Humans ; Solar wind ; Geomagnetism ; Melatonin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geography , Physics
    Notes: Abstract Data obtained from the literature on the annual pattern of human conceptions and plasma melatonin at high latitudes indicated that simple annual rhythms do not exist. Instead, prominent semiannual rhythms are found, with equinoctial troughs and solsticial peaks. A prominent semiannual environmental event is the magnetic disturbance induced by the solar wind. The semiannual magnetic disturbances are worldwide, but most pronounced in the auroral zones where the corpuscular radiation enters the atmosphere. Magnetic indices that predominantly reflect these events were obtained from the literature and correlated with the melatonin and conception data. Significant and inverse correlations were found for Inuit conceptions and the melatonin data. The correlations obtained for 48 contiguous states of the United States indicated that only the extreme northern states exhibited this relationship. These data were compared with a previous correlational study in the United States which established that sunshine was correlated with conceptions in the middle latitude and southern states. An hypothesis of dual control by electromagnetic and magnetic energies is proposed: melatonin is a progonadal hormone in humans controlled by both factors, depending on their relative strength. Other studies are reviewed regarding the possible factors involved in determining the annual pattern of human conceptions. Demographic studies of geographic variation in temporal patterns of conceptions, with particular regard to variations of the magnetic fields on the earth's surface, may provide some insight into the efficacy of these different factors.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 175 (1990), S. 107-116 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Zur Beschreibung der Polymerisationsgeschwindigkeit der radikalischen Fallungspolymerisation von Acrylsäure in Toluol wurde ein Modell entewickelt. Die experimentelle Überprüfung des Modells erfolgte durch Messungen in einem isotherm betriebenen Reaktionskalorimeter. Das Modell beschreibt die Polymerisationsgeschwindigkeit bis zum vollständigen Umsatz in einem Temperaturbereich von 40 bis 60°C.
    Notes: A kinetic model for the free-radical precipitation polymerization of acrylic acid in toluene was developed and verified experimentally by using an isothermal reaction calorimeter. The model predicts the rate of polymerization accurately up to complete conversion in the temperature range of 40 to 60°C.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 175 (1990), S. 157-168 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wird über Untersuchungen an Legierungen aus isotaktischem Polypropylen und EPDM-Elastomer berichtet, die mit hochenergetischen Elektronen bestrahlt worden waren. Die Mischungsverhältnisse in den Proben überstrichen sowohl den für elastomermodifizierte Thermoplaste typischen Bereich als auch den der thermoplasticschen Elastomeren. Eine Vernetzung der Komponenten über die Grenzfläche hinweg wurde nachgewiesen. Diese grenzflächenübergreifende Vernetzung bewirkte eine merkliche Verbesserung der mechanischen Eigenschaften insbesondere des thermoplastischen Elastomeren.
    Notes: Blends of isotactic polypropylene and EPDM rubber have been treated by electron irradiation in the composition range of rubber modification and in the thermoplastic rubber composition range as well. Mutual crosslinking of the components through the interface could be detected. This intercrosslinking caused a remarkable improvement of the mechanical properties particularly of the thermoplastic rubber.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 175 (1990), S. 205-205 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 6
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The mechanisms of photooxidation usually envisaged, are perfected by taking into account photoreactions of peroxy radicals. They involve interaction of a peroxy radical with the polymer to yield a hydroperoxy radical and a pair of macroradicals. After peroxidation, this pair will usually undergo bimolecular termination. The influence of such a reaction on photooxidation kinetics is particularly important for polyethylene. Then, chain termination occurs mainly by interaction of two hydroperoxy radicals or of a hydroperoxy radical with a macroperoxy radical. The reaction does not only affect kinetics of photooxidation but also the nature of the photooxidation products. The latter is more important for polypropylene than for polyethylene.
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  • 7
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Isothermal Differential Thermal Analysis was used to test the thermooxidative stability of pipes of polybutene during internal pressure tests at 110°C. At low hoop stresses and long testing times pipe failure was exclusively caused by thermooxidative degradation of the polymer.The stabilizer distribution in the initial state and its alteration during the pressure tests could easily be measured by isothermal DTA. Leaching of antioxidants from pipe walls could be detected. The decrease of residual thermooxidative stability was degressive.Degradation of pipe material started from the exterior pipe wall. Molecular weight of polybutene decreased rapidly after stabilizer exhaustion which could be observed by isothermal DTA.
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  • 8
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A base of experimental data on the ageing of commerial grade plastics is created. In includes assorted physical and chemical properties of plastics and their changes at natural ageing. An automated system for storing and processing of the experimental data is designed. Processing involves mathematical modeling of the changes in properties that aids in empirical prediction. The possibilities of the system are verified with experimental results from a 5-year ageing period of PE-LD and PE-HD. The results show a good agreement between the predicted and real data for selected models.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 179 (1990), S. 35-56 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Morphologie von Polypropylen-Spritzgußteilen mit Bindenaht wurde mit Röntgenweit-und Kleinwinkelstreuung, Lichtstreuung und Polarisationsmikroskopie untersucht. Die erhaltenen morphologischen Daten wurden mit mechanischen Werten aus Zugversuchen korreliert. Es wird gefunden, daß die mechanischen Eigenschaften der untersuchten Proben im wesentlichen von der sphärolithstruktur beeinflußt werden. Anhäufungen von Sphärolithen mit Kristallen der hexagonalen β-Modifikation und eine starke Inhomogenität der Sphärolithstruktur senkrecht zur Bindenaht sind der wesentliche Grund für die verschlechterten mechanischen Eigenschaften. Diese Sphärolithstruktur wird durch die Temperatur des Spritzgußwerkzeugs stark beeinflußt. Die Lamellen-Überstruktur hat dagegen einen vernachlässigbar kleinen Einfluß auf das mechanische Verhalten.
    Notes: The morphology of polypropylene plaques containing a weld line, has been investigated by x-ray wide and small angle scattering, light scattering and polarization microscopy. The results are correlated to mechanical values obtained from tensile tests. While the lamellar morphology is of neglectable influence, it is found, that the mechanical properties of the samples are strongly influenced by the spherulitic structure. Clustering of β-type spherulites and strong morphological inhomogeneities in the vicinity of the weld line are the primary reason for the mechanical weakening of the plaques. The temperature of the mould has a strong effect on the spherulitic structure and thus on the tensile properties of the samples.
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  • 10
    Electronic Resource
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    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 179 (1990), S. 77-85 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Füllstoffe für PVC- und PP-Formmassen wurden mit Mikrowellenplasma behandelt. Photoakustische FT-IR-Spektren zeigen, daß die Plasma-Polymerhülle auf der Füllstoffoberfläche —C=C—, —CH2—, CH3— und andere Gruppen enthält. Aus Röntgenelektronenspektren geht hervor, daß zwischen Siliciumdioxid und der organischen Beschichtung chemische Bindungen existieren. Durch Compoundieren von plasmabehandelten Füllstoffen mit PVC und PP werden Materialien mit guten mechanischen Eigenschaften bei niedrigen Kosten erhalten.
    Notes: Fillers for PVC and PP compounds have been treated by microwave plasma. FT-IR photoacoustic spectroscopy studies show that the plasma polymer sheath on filler's surface contains —C=C—, —CH2—, —CH3 groups, etc. X-ray photoelectron spectroscopy studies reveal that interfacial chemical bondings exist between silica and the organic coating. Application of plasma-treated fillers in PVC and PP compounds gives rise to materials of good mechanical properties and low cost.
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  • 11
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 179 (1990), S. 135-148 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Poly-(alkylenadipat)-diole mit Molmassen von 1500, 2000 und 3000 wurden bei Temperaturen von 25 und 60°C in Gegenwart verschiedener Alkohole und unterschiedlicher PUR-Katalysatoren (1,4-Diazabicyclo[2.2.2]octan (DABCO), Dibutylzinndilaurat (DBTL),Dibutylzinndiethoxid (DBTEO) und Dibutylzinnoxid (DBTO)) in Ethylacetat bzw. Toluol gelagert und die Alkoholyse verfolgt. Die erhaltenen Ergebnisse werden mit dem Alkoholyseverhalten verschiedener Dialkyladipate sowie des Lösungsmittels Ethylacetat unter den selben Bedingungen verglichen. Die Alkoholyse verlauft in Gegenwart der zinnorganischen Verbindungen etwa mit gleicher Geschwindigkeit, ohne daß diese selbst signifikant zersetzt werden, wahrend DABCO praktisch inaktiv ist. Die Aktivitat der Alkohole ist starker von ihrer sterischen Struktur als von ihrer Basizitat abhangig. Die Stabilität der Polyalkylenadipate gegenüber einer Umesterung nimmt mit der Lange der Diolalkyleneinheiten des Polyols zu. Die Umesterung von Adipinsäuredialkylestern findet auch partiell in Anwesenheit eines großen Uberschusses an Ethylacetat statt.
    Notes: Poly(alkylene adipate)diols having molar masses of 1500, 2000 and 3000 were stored at temperatures of 25 and 60°C in the presence of low amounts of different alcohols and some polyurethane (PUR) catalysts, such as dibutyltindilaurate (DBTL), dibutyltindiethoxide (DBTEO), dibutyltinoxide (DBTO), and 1,4-diazabicyclo[2.2.2]octane (DABCO). Alcoholysis was studied using either ethyl acetate (EA) or toluene as solvent. The results were compared with those obtained by examining the behaviour of several dialkyl adipates and ethyl acetate under identical conditions. The alcoholysis in the presence of the tin catalysts proceeds at the same reaction rate without significant decomposition of the catalyst, whereas DABCO is practically inactive. The nucleophilic activity of the alcohols depends on their bulk size rather than their basicity. The resistance of polyalkylene adipates to transesterification increases with the increasing alkyl chain length of diol units in polyester. A partial transesterification of dialkyl adipates takes place too, in spite of ethyl acetate being present in excess.
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  • 12
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 179 (1990), S. 157-171 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wurde das Permeations- und Trennverhalten von Alkohol/Wasser-Systemen durch poröse PVA-Membranen untersucht. PVA-Membranen mit unterschiedlicher Anzahl und Große von Poren wurden über Mischungen in Lösung mit verschiedenen synthetisierten Polymeren und Copolymeren, wie Polyacrylsäure, Polyacrylnitril, Polyacrylamid, Poly(Methylmethacrylat-co-Maleinsäureanhydrid) etc., anschließendes Gießen von Filmen und Extraktion der Polymeren oder Copolymeren durch Lösungsmittel hergestellt. Die Abhängigkeit der Durchlässigkeit und Trennwirkung von der Größe und Form der permeierenden Moleköle wurde qualitativ diskutiert. Des weiteren wurde die Selektivität der Trennwirkung in Abhangigkeit von der Zusammensetzung von Alkohol/Wasser-Gemischen und von der Größe und Anzahl der Poren untersucht. Es wurde gefunden, daß die Selektivität von der Menge und dem Molekulargewicht der in die Membranen eingebrachten Polymeren abhängt. Wenn der Gewichtsanteil des verwendeten Polymeren größer als 0,1 war, permeierte bevorzugt der Alkoholanteil bei methanolischen Msungen, wobei der Trennfaktor mit steigender Methanolkonzentration anstieg. In Gemischen mit anderen Alkoholen zeigten die Membranen andererseits eine selektive Durchlässigkeit für Wasser. Der Einfluß der Versuchsbedingungen wurde ebenfalls untersucht.
    Notes: The permeation and separation characteristics of alcohol/water systems through porous PVA membranes were investigated. Porous PVA membranes with different pore size and number were prepared by solution blending of PVA with several synthesized polymers or copolymers, such as polyacrylic acid, polyacrylamide, polyacrylonitrile, and methylmethacrylate-co-maleic anhydride, etc. Then casting, and finally extracting the blended polymers or copolymers by solvent from the membranes. The dependency of both permeation and separation on the molecular size and shape of the permeating species was dicussed qualitatively. Moreover, the permselectivity was investigated with attention to the feed composition of alcohol/water mixture and the effect of pore size and number. The selectivity was found to depend on the weight ratio and the molecular weight of polymer introduced to the membrane. When the weight ratio of polymer introduced into the membrane was larger than 0.1, methanol was permeated through membrane preferentially in methanol/water system, and the separation factor increased with increasing the methanol feed concentration. On the other hand, membrane had a selective permeability for water in the other alcohol/water systems. The influence of operating conditions was also studied.
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  • 13
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    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 175 (1990), S. 29-38 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Temperatur des T1-Minimums für die Segmentbewegung in Polypropylen, das einen hohen ataktischen Anteil besitzt, ist niedriger als die in isotaktischem Polypropylen. Ein kurzes T1, T1s, tritt bei beiden Materialien auf. Bei Temperaturerhöhung nimmt T2a (T2 der beweglichen amorphen Bezirke) stark und T2m (T2 der dazwischen liegenden Bezirke) leicht zu, während sich T2c (T2 der steifen kristallinen Bezirke) kaum ändert. T2a in Polypropylen mit hohem ataktischem Anteil ist länger als in isotaktischem Polypropylen.Der Massenbruch der kristallinen Bezirke, Fc, nimmt bei Temperaturerhöhung ab und der der amorphen Bezirke, Fa, zu. Die Relaxationsgeschwindigkeit, 1/ (T1min), steigt linear mit Zunahme des amorphen Anteils an, außer bei der mit siedendem n-Heptan extrahierten Probe. Mit Zunahme der Peaktemperatur von tan δ fällt T2a nahezu linear ab, während die Temperatur des T1-Minimums zunimmt.
    Notes: The temperature of the T1 minimum for the segmental motion in polypropylene containing a lot of atactic fraction is lower than that in isotactic polypropylene. A short T1, T1s, appears for both materials. As the temperature is raised, there is a large increase in T2a (T2 of the mobile amorphous regions), and a mild increase in T2m (T2 of the intermediate regions), while there is no substantial change in T2c (T2 of the rigid crystalline regions). T2a in polypropylene containing a lot of atactic fraction is longer than that in isotactic polypropylene.The mass fraction of crystalline regions, Fc, decreases and that of the amorphous regions, Fa, increases as the temperature is raised. There is a linear increase in the relaxation rate, 1/(T1min), as the amorphous fraction is increased, except for the sample extracted with boiling n-heptane. With increase of the peak temperature of tanδ, T2a decreases nearly linearly, while the temperature of the T1 minimum increases.
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  • 14
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    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 180 (1990), S. 191-198 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Bestrahlung von PTFE mit Elektronen niedriger Energie führt zur Abspaltung von Fluor und zum Einbau von Sauerstoff in die Polymeroberfläche. Es wird gezeigt, daß das Ausmaß der Oberflächenveränderungen hauptsächlich von der Zahl und kaum von der Energie der Elektronen abhängt, die die Oberfläche erreichen. Änderungen in der Oberflächenenergie resultieren in unterschiedlichem Benetzungsverhalten. Kontaktwinkelmessungen und Kurvenanalysen der C-1s-Peaks aus Röntgenphotonenspektroskopiemessungen zeigen, daß der am wenigsten benetzbare Teil der bestrahlten Oberflächen in den meisten Fällen aus —CF2 —CF-Einheiten besteht. Werden bei der Bestrahlung nahezu alle Fluoratome abgespalten, bleiben nur isolierte —CF2-oder —CF-Gruppen zurück. Die „receding“-Winkel werden mit zunehmender Sauerstoffkonzentration in der Oberfläche kleiner, was auf die Bildung stark oxidierter Bereiche hinweist. Die Unabhängigkeit der Kontaktwinkel von der Alterungsdauer deutet auf eine sehr geringe Beweglichkeit der Makromoleküle hin, was mit einer starken Vernet-zung an der Oberfläche zusammenhängen könnte.
    Notes: Low energy electron irradiation of PTFE induced fluorine depletion and introduction of oxygen on the surface. The effect on surface chemistry was shown to be dependent mostly on the amount of electrons reaching the sample, rather than on their energy.Changes in surface energy resulted in different wetting behaviors. The measurement of advancing water contact angles and the analysis of XPS C-1s peak shapes showed that the least wettable portion of irradiated surfaces is made in most cases of —CF2—CF — units. When the treatment caused a nearly complete fluorine depletion, only isolated —CF2— or —CF— groups are present. Receding angle values decreased linearly depending on the amount of oxygen introduced on the sample during the treatment, suggesting the formation of strongly oxidized polymer islets. The invariance of contact angles with aging time indicated very low macromolecular mobility, probably related to extensive surface crosslinking.
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  • 15
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    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 181 (1990), S. 41-52 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: In aqueous dispersions of anionic polyurethanes containing the triethylammonium salt of 2,2-dimethylol propionic acid as chain extender, triethylamine can be largely replaced by ammonia. For electrostatic reasons, NH4+ is namely more tightly bound in the ion pairs located in the Stern layer than NH(C2H5)3+. Thermal treatment of films leads to a loss of base, whereby ammonia is more rapidly released than triethylamine. Therefore, crosslinking with partially methylated hexamethylolmelamine proceeds the faster the more triethylamine is replaced by ammonia.
    Notes: In Dispersionen aus anionischen Polyurethanen, die das Triethylammoniumsalz der 2,2-Dimethylolpropionsäure als Kettenverlängerungsmittel enthalten, läßt sich durch Zugabe von Ammoniak eine weitgehende Verdrängung des Triethylamins erreichen. Aus elektrostatischen Gründen ist nämlich in den in der Sternschen Schicht lokalisierten Ionenpaaren NH4+ fester gebunden als NH(C2H5)3+. Bei der thermischen Behandlung der Filme tritt Basenabspaltung ein, dabei erfolgt die Abgabe von Ammoniak deutlich schneller als die von Triethylamin. Die Spannungswerte der mit teilmethyliertem Hexamethylolmelamin vernetzten Proben sind daher um so höher, je mehr Triethylamin durch Ammoniak ersetzt wurde.
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  • 16
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    Angewandte Makromolekulare Chemie 181 (1990), S. 53-66 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Viskoelastizitäts-Parameter von geschmolzenem Polystyrol (PS) wurden mit einem Instron-Kapillarrheometer gemessen.Die Drucknachgiebigkeit B(t) zeigt ein Plateau sowohl im Schmelze (B1)- als auch im Glaszustand (Bg); beide nehmen mit abnehmender Spannung ab. Durch Verschiebung der B(t)-Kurven werden Master-Kurven erhalten, mit denen das Gesamtdruckverhalten (überlagerte elastische und viskose Deformationen) analysiert werden kann. Die stationäre Nachgiebigkeit (Bs) erlaubt eine Beschreibung des elastischen Energieanteils und scheint mit der Extrusions-Strangaufweitung (Bcs/Bds) korreliert zu sein. Die Volumenviskosität (ηk) nimmt mit zunehmender Spannung (P), zunehmender Belastungsgeschwindigkeit (k) und abnehmender Temperatur ab.
    Notes: Viscoelastic parameters of polystyrene (PS) melt in compression creep have been measured in an lnstron capillary-rheometer.Bulk compression creep compliance B(t) shows plateau regions in the molten state (B1) and the glassy state (Bg), both decreasing with increasing stress. Shifting of B(t) curves provides master curves suitable to analysing the total (superposed elastic and viscous deformations) bulk compression behaviour. The steady-state creep compliance (Bs) allows to describe the recoverable elastic energy (Be) and seems to be related to the extrusion die swell (Bcs/Bds). Volume viscosity (ηk) decreases with decreasing stress (P), increasing compression rates (k) and decreasing temperature (T).
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  • 17
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    Angewandte Makromolekulare Chemie 181 (1990), S. 67-74 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wurden Untersuchungen über Molekulargewichtsänderungen an physikalisch bei Raumtemperatur gealterten isotaktischen Polypropylenfilamenten (iPP) mit Hilfe der Hochtemperaturgelpermeationschromatographie (HTGPC) durchgeführt. Das Ergebnis der Untersuchungen weist auf eine sehr unbedeutende Änderung des Molekulargewichts des Materials während der Alterung hin.Das Materialgranulat wurde als Bezugsstandard gewählt. Basierend auf der Uneinheitlichkeit D = Mw/Mn des Granulats wurden Filamente der Handelsprodukte GYE 47 und PXC 31399 charakterisiert, deren Alterungsdauer zwischen 2 Wochen und 8 Monaten lag. Bei den Filamenten der Qpe GYE 47 verringerte sich die Breite der Molekulargewichtsverteilung D um durchschnittlich 12%. Andererseits zeigen die Filamente des PXC 31399-vps einen weniger eindeutigen Trend zur Änderung, jedoch im Mittel hat sich die Breite der Verteilung um etwa 20% erniedrigt. Bei letzterem ist die Verteilung iiber die Alterungsdauer stark gestreut. Der GYE 47-Typ zeigt eine nahezu asymptotische Abnahme. Es wird angenommen, daß die Ungleichartigkeit in der Ändenz der Anderung von D zwischen beiden Proben in ihrer unterschiedlichen thermodynamischen Stabilitat liegen ktinnte; PXC 31399 ist weniger stabil.
    Notes: Experiments on the molecular weight variations of physically, room temperature aged isotactic polypropylene (iPP) filaments were done using the High Temperature Gel Permeation Chromatography (HTGPC). Evidence emanating from the studies indicates a very marginal change in molecular weight of the materials during aging.The granules of the materials were chosen as the reference standard. Based on the polydispersity D = Mw/Mn of the granules, filaments of commercial grades GYE 47 and PXC 31399 were characterized between an aging period ranging from 2 weeks to 8 months. The filaments of the GYE 47 grade have their distributions D lowered on the average by about 12%. On the other hand, those of the PXC 31399 grade have a less definite trend in change, but on the average, D is lowered by about 20%. The distributions of this latter grade are highly scattered over the period of aging. The GYE 47 grade shows a reduction in the distribution of a near asymptotic nature. It is believed that the disparity in the trend of change of D between the two samples could be attributed to their relative thermodynamic stability with the PXC 31399 grade being less stable.
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  • 18
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The properties (squared dimensions, anisotropy, numbers of intra- and intermolecular contacts) of a single five-way cubic lattice chain embedded into an environment (matrix) of chains of the same length n = 50 were evaluated as a function of matrix volume fraction (matrix density) v and intermolecular interaction between the matrix polymer and the minority chain segments, characterized by a parameter φ. No convincing evidence was found for the occurrence of a coil-globule transition in the range of matrix densities (v ≤ 0.7) and repulsive interactions between matrix and minority chain (φ ≤ 0.2) investigated. For moderate attractive interaction (φ ≈ -0.17) a compensation of the chaincompressing action of the matrix and the chain-expanding interaction with the matrix was observed resulting in a zero-dependence of the size and shape of the minority chain on matrix density. It further turned out that there are fixed relations among the various size and shape data irrespective of the specific combination of matrix density and thermodynamic interaction by which a particular polymer dimension is produced. These interrelations are fairly the same as those evaluated for isolated chains the size of which is varied by an intramolecular energy parameter φi.
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  • 19
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: New three phases composite materials made of glassbeads as filler, water as liquid dispersed phase and polystyrene as matrix were obtained by polymerization of a water in oil emulsion formed by water dispersed in styrene in which glass beads are added. For this purpose glass beads have to be modified by silanization by a coupling agent 3-(Trimethoxysilyl)propylmethacrylate (TPM) or a silane Octadecyltrichlorosilane (ODMS), in order to prevent the wetting of the glass by water. Only low coverage of the glass surface by the coupling agent (0,05% of TPM) are convenient for the preparation cellular materials having good mechanical properties. At higher coverage ratio, strong hydrophobic glass beads are obtained which destabilize the water / styrene emulsion and lead to macroporous products. Study of the rheology of the filled emulsion appears to be the more simple and more sensitive method to determine the level of wettability of the glass bead by the emulsion which is the most significant parameter for the preparation of such three phases composite materials. Composite materials made of glass beads, air and polystyrene are simply obtained by evaporation of water under vacuum.
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  • 20
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: To test the molecular parameters concerning gas sorption in polymers, the concentration of CO2, N2O, CO, N2, CH4 and the noble gases Ne, He in glassy poly(butylene terephthalate) films (PBTP) has been studied gravimetrically with a recording microbalance at 25°C. The sorption isotherms exhibit downward curvature to the pressure axis. As neither solubility nor adsorption can explain the experimental results, analysis was carried out based on the dual-sorption model: gas dissolution and microvoid filling are considered as independent sorption mechanisms. The parameters of the dual-sorption model for the mentioned penetrants are determined. The results indicate that for parameter correlation the Lennard-Jones potential parameters give a rough idea, but size exclusion of gases in small diameter microvoids is proposed and special chemical interactions must be considered.
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  • 21
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    Angewandte Makromolekulare Chemie 185 (1991), S. 283-292 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The ring opening metathesis polymerisation (ROMP) of 5-cyano-2-norbornene with tungsten hexachloride, tungesten oxytetrachloride, bis(dichloralkoxo)tungsten tetrachloride and bis(dichloralkoxo)tungsten oxydichloride as transition metal component was studied. Methylaluminoxan, diethylaluminium ethoxide, tetraisobutyldialuminoxan and tetrabutyltin served as cocatalyst. Toluene, Chlorobenzene and dichloromethane were used as solvents. The concentration of the tungsten components was in the range from 5 × 10-4 to 5 × 10-3 mol/l. Among the catalyst studied, tungsten hexachloride with diethylaluminium ethoxide proved to be the best. The polymerisation was highly selective with this system even at high monomer/tungsten ratios (e.q. 10200:1) and let to high conversions (≥82%).
    Notes: Die ringöffnende metathetische Polymerisation (ROMP) von 5-Cyano-2-norbornen wurde unter Einsatz von Wolframhexachlorid, Wolframoxidterachlorid, Bis(dichloralkoxo)wolframtetrachlorid und Bis(dichloralkoxo)wolframoxiddichlorid als Übergangsmetallkomponente untersucht. Als Cokatalysatoren dienten Methylaluminoxan, Diethylaluminiumethoxid, Tetraisobutyldialuminoxan und Tetrabutylzinn. Als Lösungsmittel wurden Toluol, Chlorbenzol und Dichlormethan verwendet. Die Konzentration der Wolframkomponente lag im Bereich 5 × 10-4 - 5 × 10-3 mol/l. Unter den geprüften Katalysatoren erwies sich Wolframhexachlorid in Verbindung mit Diethylalumiumethoxid als der geeignetste. Mit diesem System verlief die Polymerisation auch bei großen Monomer/Wolfram-Verhältnissen (10200 :1) hochselektiv und führte zu großen Umsätzen (≥82%).
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  • 22
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The dependence of dilution on the chain propagation and termination rate constants was investigated in the polymerization of ethyl acrylate in benzene solution at 50°C, with the rotating sector method. The errors of the above rate constants were determined and, by our method applied to decrease these errors, the errors of the propagation rate constant was reduced to its half value. By the application of our earlier results in polymerization kinetics, we found that in this system the chain propagation step is exclusively responsible for the solvent effects observed. Our experimental results can be quantitatively described in terms of the hot redical theory.
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  • 23
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    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 185 (1991), S. 329-334 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 24
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    Angewandte Makromolekulare Chemie 174 (1990), S. 1-10 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Photopolymerisation von Ethylenglykoldimethacrylat (EGDMA) mit Methylmethacrylat (MMA) wurde mit Benzoinmethylether (BME) als Initiator in einem Glasrohr durchgeführt, um einen lichtfokussierenden Plastikstab (Radius Rp) mit parabolischer Brechungsindex-Verteilung (Verteilungskonstante A) in der Nähe der Stabachse (bis zum Radius Rc) herzustellen. Die Abhängigkeit von A und Rc/Rp vom Monomerenverhältnis MMA/EGDMA der Ausgangsmischung, der Einfluß der BME-Konzentration auf die Brechungsindex-Verteilung und die Reproduzierbarkeit der Photopolymerisationen wurden untersucht. Das Rc/Rp-Verhältnis stieg mit dem Monomerenverhältnis MMA/EGDMA bei BME = 1,0 Gew.-% und der Geschwindigkeit der UV-Lampe von V = 0,58 mm/min an. Andererseits stieg Rc/Rp bei BME = 0,6 Gew.-% und V = 0,735 mm/min bis zum Monomerenverhältnis von 0,2 an und fiel dann deutlich zwischen 0,20 und 0,25 ab. Die Plastikstäbe, die hier durch Photopolymerisation hergestellt wurden, haben Linseneigenschaften und sind gut reproduzierbar.
    Notes: The photocopolymerization of ethyleneglycol dimethacrylate (EGDMA) with methylmethacrylate (MMA) containing benzoin methyl ether (BME) as initiator was carried out in a glass tube to fabricate a light-focusing plastic rod (radius Rp) with a parabolic refractive index distribution (distribution constant A) in the region near the center axis (radius Rc). The dependence of A and Rc/Rp on MMA/EGDMA feed ratio, influence of BME concentration on the refractive index distribution, and the reproducibilities of the photopolymerizations were investigated. The Rc/Rp increased with the feed ratio used under BME = 1.0 wt.-% at velocity of UV lamp V = 0.58 mm/min. On the other hand, Rc/Rp increased with the feed ratio to 0.2 and then decreased remarkably with the feed ratio in the range of 0.2-0.25 with BME = 0.6 wt.-% at V = 0.735 mm/min. Plastic rods fabricated in the investigation using photopolymerization have lens characteristics and good reproducibilities.
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  • 25
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Polystyrol- und Polymethylmethacrylateinzelfäden mit verschiedenen Graden von Doppelbrechung wurden durch die kontinuierliche Änderung der Ziehgeschwindigkeit, der Temperatur der Polymerschmelze und des Molekulargewichts von Polystyrol (PS) und Polymethylmethacrylat (PMMA) gewonnen. Der “brittle to ductile” Übergangspunkt (Übergang des Polymeren vom spröden zum ziehbaren Zustand) wurde für das optisch reine Polystyrol im Bereich der Doppelbrechungszahlen -0,6 · 10-3 bis -2,6 · 10-3 gefunden. Höhe und Lage dieses Punktes werden durch das Molekulargewicht, die Molekulargewichtsverteilung und die Temperatur der Polymerschmelze beeinflußt. Die Werte des Doppelbrechungsindexes von PS sind um zwei Zehnerpotenzen höher als von PMMA. Bei PMMA wurde der “brittle to ductile” Übergangspunkt nicht beobachtet. Die mechanischen und optischen Eigenschaften hängen nicht nur vom mittleren Wert des durch die Doppelbrechung charakteri-sierten Orientierungsgrades ab, sondern auch davon, welcher Teil des Relaxations-spektrums des Polymeren vorzugsweise orientiert ist. Beim Ziehen der PS- und PMMA-Einzelfäden bilden sich in der Mitte des Fadens Risse (crazes), die jedoch nicht an die Oberflache des Fadens treten.
    Notes: Monofilaments possessing various degrees of birefringence were obtained by changing the drawing rate, the molten polymer temperature, and the molecular weight of polystyrene (PS) and poly(methyl methacrylate) (PMMA). The “brittle-toductile” transition point of optically pure PS was found in the range of birefringences of -0.6 · 10-3 to -2.6 · 10-3. Both the height and position of this point are influenced by M̄w, molecular weight distribution, and polymer melt temperature. The birefringence of PS is higher by two orders of magnitude than that of PMMA in which this transition point has not been observed. The mechanical and optical properties depend not only on the average amount of orientation characterized by the birefringence but on what portion of the relaxation spectrum of the polymer is preferentially oriented. During the drawing of PS and PMMA monofilaments crazes are formed in the centre of the fibers and do not reach the surface.
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  • 26
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    Angewandte Makromolekulare Chemie 174 (1990), S. 105-117 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The possibility of the application of atactic polypropylene is investigated as graft base for the preparation of graft copolymers of vinyl acetate and vinyl chloride respectively graft copolymers from vinyl acetate onto polypropylene as graft base for the preparation of graft copolymers of vinyl chloride in relation to the composition of the original mixture.After compounding of the graft products with polyvinyl chloride or ABS/polyvinyl-chloride mixtures selected mechanical properties are presented in relation to the quantity and composition of the incorporated graft copolymers.
    Notes: Die Möglichkeiten des Einsatzes von ataktischem Polypropylen als Pfropfgrundlage zur Herstellung von Pfropfcopolymerisaten des Vinylacetates und Vinylchlorids bzw. von Polypropylen-Vinylacetat-Pfropfprodukten als Pfropfgrundlage zur Herstellung von Pfropfcopolymerisaten des Vinylchlorids werden in Abhängigkeit von der Ausgangsgemischzusammensetzung untersucht.Nach Abmischung der Pfropfprodukte mit Polyvinylchlorid bzw. ABS/Polyvinylchlorid-Mischungen werden ausgewählte mechanische Eigenschaften sowohl in Abhängigkeit von der Menge des enthaltenen Pfropfproduktes als auch von der Zusammensetzung der Pfropfpolymerisate dargestellt.
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  • 27
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: A new spectroscopic method for determining the permeability of ammonia in transparent polymer layers is presented. It is based on the quantitative proof of the ammonia passing the test layer into a sensor layer, containing 4-nitrophenol as an NH3-sensitive probe, which is placed under the test film. The permeability (P) of the test layer is calculated from the slope of extinction with time in the sensor layer. The lag time (t1) gives the diffusion coefficient (D). The suitability of this method is confirmed by comparison with literature values. Diffusion coefficients obtained from t1 correspond well to those obtained by the sorption method.The temperature dependence of P and D in more than five different polymers (CDA, PVB, PVAc, PVC and different polyvinyl alcohols) demonstrates that peculiarities in the temperature dependence of the permeability result from the behaviour of the NH3-solubility (P/D) which is strongly dependent on the polymer structure.
    Notes: Es wird eine neuartige spektroskopische Methode zur Messung der Ammoniak-Permeabilität in transparenten Polymerfilmen vorgestellt. Sie beruht auf dem quantitativen Nachweis des den Testfilm durchdringenden Ammoniaks in einer darunter befindlichen Sensorschicht mit Hilfe der NH3-empfindlichen Sonde 4-Nitrophenol. Aus dem Anstieg der Extinktion mit der Zeit (ΔE/Δt) in der Sensorschicht wird die Permeabilität (P) und aus der Verzögerungszeit (lag time (t1)) der Diffusionskoeffizient (D) berechnet. Die Eignung der Methode wird durch Vergleich mit Literaturwerten belegt. Die aus t1 zugänglichen Diffusionskoeffizienten stimmen sehr gut mit denen überein, die mit der Sorptionsmethode gefunden werden.Die Temperaturabhängigkeiten von P und D in mehr als fünf verschiedenen Polymeren (CDA, PVB, PVAc, PVC und in verschiedenen Polyvinylalkoholen) zeigen, daß Besonderheiten im Temperaturgang der Permeabilität aus dem vom Aufbau des Polymeren stark abhängigen Verhalten der NH3-Löslichkeit (P/D) resultieren.
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  • 28
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    Angewandte Makromolekulare Chemie 179 (1990), S. 99-111 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wurde die strahleninduzierte Pfropfung von 4-Vinylpyridin (VP) auf Styrol-Butadien-Styrol-Copolymere (SBS) in Gegenwart von gelöstem Sauerstoff untersucht. Pfropfcopolymer-Membranen mit unterschiedlichen Pfropfgraden wurden durch Gießen aus benzolischer Lösung hergestellt. Die mechanischen Eigenschaften, die Gaspermeabilität sowie der Einfluß der Temperatur auf die Gasdurchlässigkeit wurden untersucht. Der höchste Pfropfgrad von 8,4% wurde bei einer Bestrahlungszeit von 15,5 herreicht. Sowohl bei kürzeren als auch längeren Bestrahlungszeiten war der Pfropfgrad  -  bedingt durch Störung durch den vorhandenen Sauerstoff  -  niedriger. Reißfestigkeit und Reißdehnung von SBS-g-VP waren vergleichbar rnit SBS. Die Spannungsrelaxation von SBS-g-VP war langsamer als bei SBS, was auf der Bildung von starren Polyvinylpyridin(DVP)-Mikrophasen beruhen könnte, die als permanente Vernetzungspunkte wirken und die Spannungsrelaxation beeinträchtigen könnten.Da SBS eine hohe Gasdurchlässigkeit und PVP eine hohe O2/N2-Selektivität aufweisen, wurde die Gasdurchlässigkeit der Pfropfmembranen untersucht. Die Selektivitat der SBS-g-VP-Membranen stieg mit steigendem Pfropfgrad, allerdings auf Kosten der Permeabilität, Bei Erhöhung der Temperatur nahm die Durchlässigkeit zu, das Verhältnis O2/N2, aber ab. Die Aktivierungsenergie (Ep) der Gasdurchlässigkeit stieg mit dem Pfropfgrad. Für eine nichtgepfropfte SBS-Membran betrug Ep 5,5 kcal/mol für Sauerstoff und 7,2 kcal/mol für Stickstoff. Für eine SBS-g-VP-Membran mit einem Pfropfgrad von 8,4% waren die Ep-Werte für Sauerstoff und Stickstoff 6,5 bzw. 8,1 kcal/mol.
    Notes: The grafting of 4-vinyl pyridine (VP) onto styrene-butadiene-styrene triblock copolymers (SBS) by homografting irradiation with dissolved oxygen was studied. Homograft membranes of various degree of grafting were prepared from a casting solution of grafted copolymer in benzene. The mechanical properties of membranes, gas permeability, and the effect of operating temperature on gas permeation were investigated.The degree of grafting of 8.4% was the largest at an irradiation time of about 15.5 h. It was smaller at both shorter and longer duration because of the interference of dissolved oxygen. It was found that the tensile strength and elongation of SBS-g-VP were similar to those of SBS. The stress relaxation of SBS-g-VP was slower than that of SBS, and this might be due to the formation of rigid microphase separation domain of poly(4-vinyl pyridine), which acted as permanent crosslinking points to reduce the stress relaxation.Using the properties of high flux of SBS and high O2/N2 selectivity of poly(4-vinyl pyridine), the performance of gas permeation of 4-vinyl pyridine homografted SBS membrane was studied. The selectivity of SBS-g-VP membrane increased with increasing degree of grafting. However, it was done at the expense of a decrease in the gas permeability.When the operating temperature of gas permeation increased, the permeability of oxygen and nitrogen increased, and the O2/N2 permeability ratio decreased. The activation energy (Ep) for gas permeation through different degree of grafting of SBS-g-VP membrane (obtained by the Arrhenius law) increased with increasing degree of grafting. For ungrafted SBS membrane, Ep was 5.5 kcal/mol for oxygen and 7.2 kcal/mol for nitrogen. For 8.4% grafting degree SBS-g-VP membrane, Ep for oxygen and nitrogen, were 6.5 and 8.1 kcal/mol, respectively.
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  • 29
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    Angewandte Makromolekulare Chemie 175 (1990), S. 13-27 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The change of molecular mass and long-term strength of high and low density polyethylene under tensile load in surface-active medium was studied. It is shown that long-term strength of polyethylene depends on the molecular mass. The influence of polydispersity on strength was investigated.
    Notes: Es wird über die Untersuchungsergebnisse von Lebensdauer und Molmassenänderung an polydispersen Proben von HDPE und HDPE in einem breiten M̄v-Bereich im Zugversuch in einem oberflächenaktiven Medium berichtet.Die Arbeit enthält auch die Darstellung der quantitativen Änderung der Molmasse von Hochdruck- und Niederdruck-Polyethylen unter Dauerbeanspruchung und die Analyse der Lebensdauer in Abhängigkeit von den unterschiedlichen Molmassen (MM) (M̄w, M̄n, M̄v); die Unterschiede in Abhängigkeit von der Lebensdauer von M̄v für Proben und polydisperse Muster sowie die Vorstellungen über den dualen Einfluß der Polydispersität auf die Lebensdauer mit einer Interpretation der auftretenden Erscheinungen werden beschrieben.
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  • 30
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: One constitutive property for the description of dyeing polyester-materials with disperse dyes is the particle size distribution in the dye bath. To measure particle sizes below one micrometer in situ, special techniques are required. One of these is the so called photon-correlation-spectroscopy, depending on the scattering of laser light by suspended small particles in a fluid. The mathematical and physical principles of the photon-correlation-technique are explained in this article.
    Notes: Eine zur Beschreibung des Färbevorganges von Polyestermaterialien mit Dispersionsfarbstoffen wesentliche Größe stellt die Partikelgrößenverteilung im Farbebad dar. Partikelgrößen unterhalb eines Mikrometers lassen sich in situ nur mit wenigen Meßtechniken bestimmen. Dazu zählt u. a. die Photonen-Korrelations-Spektroskopie, die auf Streuung von Laserlicht an kleinen, in einer Flüssigkeit suspendierten Teilchen basiert. Die mathematischen und physikalischen Grundlagen dieser Meßtechnik werden in diesem Artikel erläutert.
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  • 31
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    Angewandte Makromolekulare Chemie 175 (1990), S. 81-97 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Kristallinität von Polyethylen, Polyethylenterephthalat und Polypropylen wurde mit Hilfe der Röntgenweitwinkel(WAXS)-und-kleinwinkel(SAXS)streuung gemessen. Die mittels der letzteren Methode erhaltenen Kristallinitätswerte sind deutlich größer als die durch WAXS. Es wird vermutet, daß die Unterschiede mit der Schicht zusammenhängen, die zwischen den amorphen und kristallinen Bereichen liegt. Daraus wurde geschlossen, daß die Röntgenkleinwinkelstreuung nicht als unabhängige Routinemethode zur Kristallinitätsbestimmung angewendet werden kann.
    Notes: The crystallinity of polyethylene, polyethyleneterephthalate, and polypropylene was measured with the aid of wide angle (WAXS) and small angle (SAXS) X-ray scattering methods. The values of crystallinity evaluated using the latter method are distinctly larger than those ones given by the WAXS method. The differences are supposed to be associated with the transition layer existing between the amorphous and crystalline regions. It was concluded that small angle X-ray scattering cannot be employed as an independent routine method of crystallinity determination.
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  • 32
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    Angewandte Makromolekulare Chemie 175 (1990), S. 117-128 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Für das System Cellulosenitrat-μ-Styragel-THF wurde die DP-Ve-Beziehung sowie die Ausarbeitung der betreffenden Eichparameter einer genaueren Betrachtung unterzogen. Die etwa dreißig Eichpräparate waren durch definierten säurekatalysierten Abbau von Baumwollcellulose und anschließende Nitrierung hergestellt worden und umfaßten einen DP-Bereich von 150 〈 DP 〈 8000. Es wird gezeigt, daß mit steigendem DP die DP-Ve-Beziehung drei verschiedene Phasen aufweist. Bei der Anwendung der SEC auf Cellulosenitrat müssen daher bezüglich der Eichung zwei Fehlerquellen in Betracht gezogen werden: eine bezieht sich auf die Methode der Ausarbeitung der Eichparameter als solche, und die andere auf die Nichtbeachtung des Vorhandenseins dreier Abschnitte in der DP-Ve-Beziehung. Die Auswirkung dieser Fehler auf die Genauigkeit der aus den Elutionsdiagrammen abgeleiteten Verteilungskurven und DP-Mittelwerte wird diskutiert.
    Notes: The calibration behaviour of the system cellulose nitrate-μ-Styragel-THF has been studied using about 30 different calibration samples prepared by defined acid catalyzed degradation of cotton cellulose. The samples covered a range of DP between 150 〈 DP 〈 8000. It is shown that the DP-Ve relationship is characterized by the existence of three subsequent stages. Consequently, two sources of errors in the DP-Ve calibration must be taken into consideration. One refers to the methods as such to elaborate the calibration parameters, and the other one arises by neglecting that the DP-Ve relationship involves 3 distinct stages. The extent of the two classes of errors in regard to the exactness of the determined molecular weight averages and molecular weight distributions is discussed.
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  • 33
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    Angewandte Makromolekulare Chemie 175 (1990), S. 141-156 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Bei der Polycondensation von d,l-Asparaginsäure mit Nδ-phthaloyl-L-ornithin in Phosphorsäure bei 185°C entstehen statisticsche Copolymere (Ausbeute 60  -  70%) aus Poly(d,l-succinimid-co-Nδ-phthaloyl-d,l-ornithin), Formel 6, mit inhärenten Viskositäten (DMF) von 5 bis 15 ml g-1. Copolyimide der selben Zusammensetzung 6 und vergleichbarer Kettenlänge werden aus Asparaginsäure und dem Kupferchelat des Phthaloylornithins erhalten. Die Behandlung des Copolymeren 6 mit Hydrazinhydrat fuhrt zur Öffnung der Succinimid-Kettenglieder unter Bildung von Hydrazid-Seitengruppen. Die resultierenden Polyamide sind Poly(α,β-d,l-asparaginsäurehydrazid-co-d,l-ornithin), Formel 7. Kürzere Reaktionszeiten bedingen unvollständige Ringöffnung, und die verbleibenden Succinimid-Gruppen werden bei der folgenden Aufarbeitung hydrolytisch gespalten unter Bildung von Asparaginsaüre-Gruppen; die sogebildeten Polyamide besitzen die Struktur 8. Beide Polymere, 7 und 8, sind in Wasser loslich und zeigen in Wasser inharente Viskositiiten von 5 bis 14 ml g-l. Die Fahigkeit dieser Polyamide zur Arzneimittelverankerung wird durch Ankoppeln von Carbonsau- ren als Modellsubstanzen gezeigt.
    Notes: The polycondensation of d,l-aspartic acid with Nδ-phthaloyl-l-ornithine in phosphoric acid at 185°C gives rise to the formation, in 60  -  75% yield, of random copolymers of the poly(d,l-succinimide-co-Nδ-phthaloyl-D,L-ornithine) type 6 possessing inherent viscosities (DMF) in the range of 5  -  15 ml g-1. Copolyimides of the same compositions 6 and comparable chain lengths are obtained from aspartic acid and the copper chelate of the phthaloylornithine. Treatment of copolymers 6 with hydrazine hydrate in DMF leads to N-deprotection and opening of the intrachain succinimide rings with formation of hydrazide side groups. The resultant polyamides are of the poly(α,β-d,l-asparthydrazide-co-d,l-ornithine) type 7. Shorter reaction periods give incomplete hydrazinolytic ring opening, and the remaining succinimide units are cleaved hydrolytically during the subsequent aqueous workup, thereby transforming into aspartic acid units. The polyamides so formed possess the general poly(α,β-d,l-asparthydrazide-co-α,β-d,l-aspartic acid-co-d,l-ornithine) structure 8 Both types 7 and 8 are soluble in water and, in this medium, give inherent viscosities of 5  -  14 ml g-1. The potential drug-anchoring capabilities of these amine-functionalized polyamides are demonstrated by coupling reactions with model carboxylic acids.
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  • 34
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Im Zusammenhang mit Arbeiten über den Wirkungsmechanismus von Antioxidantien in Kohlenwasserstoffpolymeren unter Sauerstoffmangel wurde die Abfangreaktion des Modellradikals 1-Cyano-1-methylethyl (R°) mit N-Isopropyl-N′-phenyl-1,4-phenylendiamin (Ia) und seinem Oxidationsprodukt IIa untersucht. Reines Ia und IIa reagieren kaum mit R′, eine Mischung aus beiden ist jedoch ein effektiver Fänger fur R′, wobei R′ entweder am Stickstoffatom zwischen den aromatischen Ringen unter Bildung von VIa gebunden wird, oder unter Substitution mit dem Phenylenring reagiert, wobei VIIIa entsteht. Verbindung VIa ist labil, bei Vulkanisationstemperatur spaltet sie im neutralen Medium Olefin unter Regenerierung von Ia ab. In Gegenwart von Säuren lauft diese Reaktion auch bei niedrigerer Temperatur ab. Im Produkt VIIIa ist R′ fest gebunden, durch die Nitrilgruppe tritt jedoch eine säurekatalysierte Cyclisierung zum Indolinderivat X ein. Die Bildung von VIIIa ist ein Modell für die Entstehung einer „nichtextrahierbaren Fraktion“ des Antioxidants Ia bei der Stabilisierung von Kohlenwasserstoffpolymeren.
    Notes: In connection with the investigation of the mechanism of antioxidant action of antidegradants in hydrocarbon polymers under the conditions of a relative deficiency of oxygen, scavenging of a model alkyl (1-cyano-1-methylethyl,R°) was studied with Nisopropyl-N′-phenyl-1,4-phenylenediamine (Ia)For abbreviations see p. 11. and its oxidation product, i.e. Nisopropyl-N′-phenyl-1,4-benzoquinonediimine (IIa). While pure Ia and IIa do not react with the radical R° almost at all, their mixture is able to scavenge R° effectively. The reaction is further accelerated with acids. The alkyl R° combines with the antidegradant molecule in two ways, one of which leads to the substitution at the nitrogen atom between the aromatic rings, giving rise to VIa, while the other consists in the substitution of phenylene, leading to VIIIa. The product VIa is labile, and at vulcanization temperatures it readily splits off olefin in a neutral medium, being regenerated to Ia. In the presence of acids this reaction proceeds even at lower temperatures. In the other product, i.e. in VIIIa, the alkyl R° is bound firmly, but due to the presence of the nitrile group, VIIIa is readily cyclized by the effect of acids, and an indoline derivative X is formed. The formation of VIIIa is a model of the formation of an “unextractable fraction” of antidegradant Ia in the stabilization of hydrocarbon polymers. Investigations based on the isolation of reaction products bear at the same time evidence of the possibility of regeneration of an effective antioxidant in the stabilized substrate.
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  • 35
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The photochemical degradation of polymers (commonly known as UV degradation) takes place in two stages: First, there is the primary process comprising the rapid formation of radicals caused by quanta of visible light; this involves the dissociation of polymer chain molecules and/or the activation of polymer chain molecules respectively of additives, colorants and impurities contained in the polymer. The secondary process consists in oxidation reactions with singulett-oxygen generated by energy-transfer and/or between the polymer radicals thus formed and adsorbed oxygen, as a result of which gradual degradation of the polymer takes place.An investigation of these individual reactions using a combination of selected physical test methods leads to an unterstanding of the entire reaction sequence involved in photo-oxidative degradation. This knowledge provides a basis for systematically improving the weather-resistance of polymers by modifying their basic polymeric structure or through the controlled use of UV absorbers, quenchers, radical interceptors and antioxidants.The physical test methods themselves are divided into two categories: techniques used for investigating the primary processes (ultra short-time spectroscopy, ESR) and those used to investigate the secondary processes (XPS, FT-IR, UV/VIS et al.).With pigmented polymers, attention is focussed on borderline cases in the use of photoactive and photoinactive pigments: as a result of “photocatalytic oxidation”, photoactive pigments (e.g. TiO2 anatase) lead to additional degradation reactions which take place at the same time as the UV degradation reaction. Photoinactive pigments (e.g. high-grade TiO2-rutile and iron oxide pigments), on the other hand, exhibit negligible or no photocatalytic oxidation and, by absorbing UV radiation, provides better protection for the polymer against UV degradation.This paper gives an overview of the above-mentioned physical methods of investigating primary and secondary photochemical processes, taking a thermoplastic material (Polycarbonate) as an example. A description is also given of the photocatalytic oxidation reations which can take place if pigmented polymers are used, and there is a discussion of the degradation-inhibiting effects of inorganic pigments.
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  • 36
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The aim of the present work is to predict the warehouse storage life of polyethylene low-density, polyethylene high-density and polystyrene impact-resistent, using the method of temperature-time superposition. The properties, most representative for thermal ageing, are the relative elongation at break for polyethylene and the impact resistance for polystyrene. The validity of the predicted shelf-life is verified by estimating the change of these properties under real conditions of warehouse storage.
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  • 37
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A commercial type of impact-resistant polystyrene was investigated. Two types of antioxidants, Irganox 245 and Irganox PS-800 were added to polystyrene in ammounts of 0,05 to 0.20%. Films, dumbbells and straight test pieces were subjected to thermal and u.v. ageing. Films of 250 μ thickness were thermally treated at 100°C and separately u.v. irradiated at 360 nm for 24, 72, 120 and 168 hours. Dumbbells and straight test pieces were only thermally aged at 100°C for 7, 14, 21, 28 and 35 days. Mechanical properties were determined. The spectra of samples were recorded using Perkin-Elmer, model 1750 FTIR and Perkin-Elmer data station 7700. Colour changes of all dumbbells were measured using Elrepho apparatus in u.v.-visible region. (Changes of the content of carbonyl and hydroxyl groups, as well as of polybutadiene (PB) unsaturation in films were recorded on i.r. spektrophotometer Perkin-Elmer 257 between 4000 and 625 cm-1 and were published in the first part of this study1).
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  • 38
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    Angewandte Makromolekulare Chemie 181 (1990), S. 85-91 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Formstoffe aus aromatischen Polyepoxiden, aromatischen Polyaminen mit hochtemperaturbeständigen Strukturelementen sowie pulverförmigen Füllstoffen besitzen hervorragende Eigenschaften, wie hohe Glasübergangstemperatur, hohemechanische Festigkeit, kleinen thermischen Ausdehnungskoeffizienten und Schwerbrennbarkeit ohne Zugabe von Flammschutzmitteln. Über die Synthese dieser aromatischen Polyamine, die Herstellung und Verarbeitung der Niederdruckpreßmassen sowie die Eigenschaften der Formstoffe wird berichtet.
    Notes: Moulded materials produced from aromatic epoxide resins, aromatic polyamines with high-temperature-resistant structure units and powdered mineral fillers possess outstanding properties like high glass transition temperatures, high mechanical strength, low linear thermal expansion coefficient, and reduced flammability without the addition of flame retardants. An account is given of the synthesis of aromatic polyamines, the preparation and working of moulding materials and the properties of the finished products.
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  • 39
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    Angewandte Makromolekulare Chemie 190 (1991), S. 1-14 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Durch gemeinsame Reaktion von Benzophenontetracarbonsäuredianhydrid, Maleinsäureanhydrid und Diaminen mit 1,3,5-Triazingruppen wurden niedermolekulare Prepolymere mit Amin-Endgruppen erhalten, die sowohl 1,3,5-Triazingruppen als auch Etherbindungen enthalten. Diese reaktiven Prepolymeren sind in niedrigsiedenden Lösemitteln wie z. B. Chloroform und Tetrahydrofuran löslich. Sie wurden durch Elementaranalyse, IR- und NMR-Spektroskopie, Dampfdruckosmometrie und Viskosimetrie charakterisiert. Beim Erhitzen der Prepolymeren auf Temperaturen zwischen 180 und 190°C tritt Kettenverlängerung durch Michael-Addition auf; gleichzeitig vernetzen sie durch Reaktion der Amin- mit den Maleimid-Endgruppen. Die vernetzten Polymeren sind thermisch stabil; ihr thermisches Verhalten wurde durch TGA, DTA und isotherme Alterung untersucht. Die Biegefestigkeit und interlaminare Scherfestigkeit von aus den Prepolymeren und Carbonfasergeweben hergestellten Laminaten wurden gemessen.
    Notes: Low molecular weight amine-terminated monomaleimide prepolymers containing 1,3,5-triazine groups as well as ether linkages were synthesized by reacting benzophenone tetracarboxylic dianhydride, diamines having 1,3,5-triazine group and maleic anhydride. These reactive prepolymers are soluble in low boiling solvents such as chloroform, tetrahydrofuran etc. They were characterized by elemental analyses, IR and NMR spectroscopy, vapour pressure osmometry, and viscosity. On heating at 180-190°C these prepolymers undergo simultaneous chain extension by Michael addition reaction and crosslinking by mutual reaction between their amine-terminated and maleimide-terminated ends. The cured polymers are thermostable and the thermal behaviour was studied by TGA, DTA, and isothermal aging. Laminates fabricated using these prepolymers and carbon fiber as reinforcing agent were evaluated by their flexural strength and interlaminar shear strength.
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  • 40
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    Angewandte Makromolekulare Chemie 190 (1991), S. 15-32 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Ein Epoxidharz wurde durch Reaktion mit Anilin bzw. Benzylamin in unterschiedlichen molaren Verhältnissen modifiziert. Die modifizierten Harze wurden dann mit Diethylamin und anschließend mit teilblockiertem Toluylendiisocyanat umgesetzt, wobei thermisch vernetzbare Harze mit tertiären Aminen in und am Ende der Polymerkette erhalten wurden. Die partielle Ansäuerung mit Essigsäure lieferte thermisch vernetzbare kationische Harze, aus denen durch Lösen in geeigneten Lösungsmitteln und Zugabe von entionisiertem Wasser Emulsionen hergestellt wurden. Diese wurden hinsichtlich ihrer Eignung zur elektrolytischen Abscheidung untersucht und verglichen. Die Ergebnisse zeigen, daß die Abscheidungsausbeute und das Streuvermögen der Emulsionen aus Benzylamin-modifizierten Epoxidharzen besser sind als die der Anilin-modifizierten Epoxidemulsionen. Ein hohes, vom pH-Wert der Emulsion abhängiges Streuvermögen ist für diese kationischen Harze charakteristisch.
    Notes: Aniline/benzylamine-modified epoxy resins with different molecular weights, which contain tertiary amines in the middle of the polymer chain, were synthesized by the reaction of aniline/benzylamine with epoxy resin at various molar ratios. The resulting aniline/benzylamine-modified epoxy resins were reacted with diethylamine and subsequently reacted with 2-ethylhexanol-blocked toluene diisocyanate to obtain thermally crosslinkable resins which contain tertiary amines at the end and in the middle of the polymer chain. These resins were partially neutralixed with acetic acid to give thermally crosslinkable cationic resins. The resulting cationic resins were dissolved in suitable solvents and mixed with deionized water to form various emulsions. The emulsion and electrodeposition properties of these resins were studied in some detail to compare the properties of these cationic resins. The results show that the deposition yields and throwing power of the emulsions prepared from benzylaminemodified epoxy resins are higher than those of the emulsions prepared from anilinemodified epoxy resins. The emulsion having proper pH values can give a high throwing power. High throwing power is the characteristic property of these modified cationic resins. Factors determining the throwing power and deposition yield of the emulsions were also investigated.
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  • 41
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Arylacrylsäuren, wie Furylacrylsäure und Thienylacrylsäure können durch Knoevenagel-Reaktion der Arylcarbaldehyde mit Malonsäure in Pyridin dargestellt werden. Durch einfache Veresterung der Arylacrylsäuren in Methanol/Schwefelsäure werden die entsprechenden Arylacrylsäuremethylester mit guten Ausbeuten erhalten. Diese isomerisieren bei Bestrahlung mit UV-Licht (λ ≥ 280 nm) in methanolischer Lösung. Bei der Photoreaktion in Lösung wurde keine Photodimerisierung beobachtet. Die Reaktionskinetik der Photoreaktionen wurde untersucht.
    Notes: Aryl acrylic acids, e. g. furyl acrylic acid or thienyl acrylic acid are readily formed by the Knoevenagel condensation reaction of arylcarbaldehydes and malonic acid in pyridine. Esterification of these acids with methanol/sulfuric acid gives the corresponding aryl acrylic acid methyl esters in good yields. In methanolic solution these methyl esters isomerize upon irradiation (λ 280 nm). No photodimerization was observed. Kinetic data are given.
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  • 42
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    Angewandte Makromolekulare Chemie 190 (1991), S. 67-80 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Different composite materials, with retified or natural poplar and polyester resin were prepared by molding. The influence of the filler granulometry on certain physicochemical (density, humidity, hardness) or mechanical properties of the materials was studied. The density and the increase of mass in humid atmosphere were always found to be less when the wood was thermally treated. On the other hand, the hardness of the composites made from natural poplar was much higher. The mechanical properties were found to be weak when the wood was retified.When the wood was thermally treated, it was possible to optimise the three parameters, namely, density, water retention capacity and mechanical properties. The optimal granulometry of poplar was determined between 0.75 and 1.5 mm.The results obtained are discussed considering the physico-chemical properties of the different varieties of wood studied and the interactions which exist between the polar resin and the wood.
    Notes: Divers matériaux composites à base de peuplier rétifié ou naturel et de résine polyester insaturée ont été préparés par moulage. L'influence de la granulométrie de la charge a été étudiée sur quelques propriétés physico-chimiques (densité, reprise d'humidité, dureté) ou mécaniques des matériaux obtenus. La densité et la reprise de masse en milieu humide sont toujours plus faibles si la charge est traitée thermiquement sous atmosphère inerte. Par contre, la dureté des composites issus du peuplier naturel est plus importante. Les propriétés mécaniques sont inférieures si la charge est rétifitée.Si la charge lignocellulosique est traitée thermiquement, il est possible d'optimiser les trois paramètres: densité, reprise d'eau et propriétés mécaniques; la granulométrie optimale du peuplier est ainsi comprise entre 0,75 et 1,5 mm.Les résultats obtenus sont expliqués en tenant compte des propriétés physico-chimiques des charges et des interactions existant entre la résine polaire et le bois.
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  • 43
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die vorliegende Arbeit untersucht das Wasserdurchlässigkeitsverhalten von vier Arten verschieden modifizierter Chitosanmembranen zur Abtrennung von Wasser aus wäßrigen Ethanolmischungen. Chitosan wurde aus Chitin von Krebstierschalen durch Verseifung (Deacetylierung) gewonnen. Die in dieser Arbeit untersuchten modifizierten Chitosanmembranen enthielten Carboxymethyl-, Carboxyethyl-, Cyanethyl- und Amidoxim-Chitosan. Die Einführung hydrophiler funktioneller Gruppen in der 6-O Position des Chitosans erhöht die Selektivität der modifizierten Membranen im Vergleich zu den mit Essigsäure komplexierten Chitosanmembranen. Die Untersuchungen zeigen, daß Chitosanmembranen, die Carboxygruppen enthalten, die höchste Wasserdampfdurchlässigkeit aufweisen. Carboxymethyl-Chitosanmembranen zeigen eine maximale Quellung und den höchsten Ethanoldurchfluß bei einer Ethanolkonzentration von ca. 15 Gew.-% im Zulauf aufgrund von Bindungs- und Weichmachereffekten.
    Notes: The present study investigates the pervaporation performance of four kinds of modified chitosan membranes to separate water from aqueous ethanol solution. Chitosan was prepared from chitin abstracted from the crab shell and subsequently deacetylated with aqueous NaOH solution. Modified chitosan membranes examined in this study include carboxymethyl chitosan, carboxyethyl chitosan, cyanoethyl chitosan, and amidoxime chitosan. The incorporation of hydrophilic functional groups into the 6-O position of chitosan enhances the selectivity of modified chitosan membrane compared to the previously reported chitosan-acetic acid complex membrane. Among the modified chitosan membranes, membranes containing carboxy groups show the best pervaporation performance. Carboxymethyl chitosan membranes show the maximum swelling and ethanol flux at approx. 15 wt.-% feed ethanol concentration due to the coupling and plasticizing effect.
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  • 44
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The tensile properties of self reinforced poly(propylene)/poly(1-butene) composites, obtained by rapid extension of the melt, have been measured and correlated to morphological parameters derived from x-ray experiments. Critical fiber lengths as a function of sample composition and the elastic modulus and yield stress of the fibers could be determined. It is shown, that, applying a load to the system, the forces are fully taken up by the fibers and the system breaks by fail of the fibers. The longitudinal structure of the fibers is found to be independent of sample composition.
    Notes: Mechanische Parameter wie Elastizitätsmodul, Fliß- und Bruchspannung von aus der hochorientierten Schmelze hergestellten nadelkristallinen Mischungen aus Poly(propylen) und Poly(1-bute) wurden mit morphologischen Parametern, die aus Röntgenmessungen abgeleitet wurden, korreliert. Es wird gezeigt, daß der Elastizitätsmodul des Verbundes aus den E-Moduln der Fasern und der Matrix berechnet werden kann (Mischungsregel). Die an der Probe angreifenden Kräfte werden voll auf die Fasern übertragen; der Verbund kann daher als eigenfaserverstärktes System angesehen werden. Die Abschätzung der kritischen Faserlänge ergibt, daß die Festigkeit der FAsern voll ausgenutzt wird; der Bruch des Systems bei Belastung ist daher auf das Versagen der Fasern zurückzuführen. Das mechanische Verhalten des Verbundes wird stark beeinflußt durch die Komponentenzusammensetzung. Die longitudinale Struktur der Nadeln beider Komponenten bleibt unbeeinflußt von der jeweiligen Co-Komponente.
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  • 45
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    Angewandte Makromolekulare Chemie 192 (1991), S. 199-211 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Lösliche kationische Polyelektrolyte mit quartären Stickstoffatomen in der Hauptkette wurden durch Polykondensation von Epichlorhydrin (ECH) mit Dimethylamin (DMA) und N,N-Dialkylaminoakylaminen erhalten. Die Reaktionsparameter, die die Polymereigenschaften hauptsächlich beeinflussen, sind: Molverhältnis DMA/asymmetrische Diamine, Ausgangskonzentration der Aminlösung, Molverhältnis ECH/Amine und die Struktur der asymmetrischen Diamine. Das viskosimetrische Verhalten verdünnter wäßriger Lösungen mit oder ohne Zugabe neutraler Salze veranschaulicht die flexible Natur der Polyelektrolyten.
    Notes: Water soluble cationic polyelectrolytes containing quaternary nitrogen atoms within the main chain were prepared via condensation polymerization of epichlorohydrin (ECH) with dimethylamine (DMA) and N,N-dialkylaminoalkylamines. The main parameters of the reaction that influence the polymer properties are: DMA/asymmetrical diamine molar ratio, the initial concentration of amine solution, NaOH/amine molar ratio, ECH/amine molar ratio, and asymmetrical diamine structure. The feature of flexible polyelectrolyte own to the investigated polymers was emphasized by the viscosimetric behaviour in dilute aqueous solutions with and without salt presence.
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  • 46
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    Angewandte Makromolekulare Chemie 192 (1991), S. 213-213 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 47
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    Angewandte Makromolekulare Chemie 193 (1991), S. 1-11 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Antioxidantien wurden in einer modifizierten Friedel-Crafts-Reaktion mit wasserfreiem Zinkchlorid als Katalysator an Flüssig-Naturkautschuk mit Hydroxy-Endgruppen gebunden. Die immobilisierten Antioxidantien waren weniger flüchtig und extrahierbar als konventionelle Antioxidantien. Sie wurden sowohl einem Latex als auch trockenem Kautschuk zugesetzt; die daraus hergestellten Vulkanisate zeigten eine bessere Alterungsbeständigkeit als Vulkanisate mit konventionellen Antioxidantien.
    Notes: Antioxidants were attached to hydroxy-terminated liquid natural rubber by modified Friedel-Crafts alkylation reaction using anhydrous zinc chloride as catalyst. The rubber bound antioxidants were found to be less volatile and less extractable compared to conventional antioxidants. The bound antioxidants were tried both in latex compounds and dry rubber compounds. The vulcanizates showed improved ageing resistance compared to vulcanizates based on conventional antioxidants.
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  • 48
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    Angewandte Makromolekulare Chemie 193 (1991), S. 13-20 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Strom-Spannungs-Charakteristik eines Bisphenol-A-Polycarbonats im Span-nungsbereich 50-1000 V und der Einfluß von UV-Bestrahlung (λ = 225 und 300 nm) und Tempern auf die elektrische Leitfähigkeit (σ) des Polycarbonats wurden untersucht. Die Abhängigkeit von σ gegen 1/T deutet auf zwei verschiedene Leitfähigkeits-mechanismen hin. Aus den Ergebnissen wurden die Aktivierungsenergien der Leitfähigkeit und die Sprungdistanzen berechnet.
    Notes: Current-voltage characteristics of polycarbonate samples (PC) have been studied in the voltage range 50-1000 V. The effect of UV-irradiation at λ = 225 and 300 nm, and thermal annealing on the electrical conductivity (σ) of PC was studied. The σ vs. 1/T relationship shows two slopes, i.e. two possible conduction mechanisms. The obtained results made it possible to determine a complete set of conduction parameters including activation energy and jump distance.
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  • 49
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    Angewandte Makromolekulare Chemie 193 (1991), S. 21-28 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Durch Suspensionspolymerisation wurden Terpolymere aus Acrylnitril (AN), Vinylacetat (VA) (7,5-30 mol-%, bezogen auf AN) und Divinylbenzol (DVB) (10 Gew.-%) hergestellt. Als Verdünner wurden Mischungen von Toluol oder Cyclohexanol (90 Vo1.-%) mit Hexadecan, Octan, Dodecan, 2-Ethylhexanol oder Benzylalkohol (jeweils 10 Vo1.-%) verwendet.Die Porosität der AN-VA-DVB-Terpolymeren ist mit 0,61-0,68 größer als die der entsprechenden AN-DVB-Copolymeren. Die übermolekulare Struktur der Terpolymeren hängt vom verwendeten Verdünner ab, obwohl sich die Porositäten nicht sehr voneinander unterscheiden. Die beim Erhitzen der Terpolymeren auf Temperaturen über 200°C auftretenden thermischen Effekte sind signifikant größer als die bei der Cyclisierung von AN-Polymeren gemessenen.
    Notes: Terpolymers of acrylonitrile (AN), vinyl acetate (VA) (7.5-30 mol-%, related to AN), and divinylbenzene (DVB) (10 wt.-%) were prepared by suspension polymerization. The diluents used were mixtures of toluene or cyclohexanol (90 vol.-%) with solvents (10 vol.-%) such as hexadecane (HD), octane (O), dodecane (D), 2-ethylhexanol (E) or benzyl alcohol (B).It has been found that AN-VA-DVB terpolymers have a higher porosity, about 0.61-0.68, than corresponding AN-DVB copolymers. The terpolymers obtained with mixtures of various diluents differ in their supermolecular structure although they had similar porosity characteristics.The thermal effects accompanying heating of the terpolymers above 200°C significantly exceed that of nitrile groups cyclization observed of the other AN polymers.
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  • 50
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    Angewandte Makromolekulare Chemie 193 (1991), S. 39-49 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die rheologischen und mechanischen Eigenschaften von Blends aus PE-HD und zwei verschiedenen PE-LLD-Typen wurden im gesamten Mischungsbereich gemessen. Die Polymeren sind im festen Zustand und in der Schmelze ausreichend verträglich, so daß ihre vorteilhaften Eigenschaften genutzt werden können.
    Notes: A high density polyethylene grade is blended with two selected grades of linear low density polyethylene and the mechanical and rheological properties of the blends are evaluated over the entire composition range. The blends show sufficient compatibility in the solid phase and in the melt and hence they can be advantageously used to capitalize on their useful properties.
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  • 51
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    Angewandte Makromolekulare Chemie 192 (1991), S. 51-55 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: N,N-Dimethylacrylamid (DMA) und Isopropylmethacrylat (IPM) wurden in Dimethylformamid mit Azoisobutyronitril als Initiator copolymerisiert. Die Copolymerzusammensetzung wurde 1H-NMR-spektroskopisch ermittelt. Die Copolymerisationsparameter (rDMA = 0,58, rIPM = 2,76) wurden nach Kelen-Tüdős berechnet.
    Notes: Copolymers of N,N-dimethyl acrylamide (DMA) and isopropylmethacrylate (IPM) were prepared in dimethyl formamide using azoisobutyronitrile as initiator. The composition of copolymers was determined by 1H-NMR analysis. Reactivity ratios (rDMA = 0.58, rIPM = 2.76) were calculated from these values by using the Kelen-Tüdős differential linear equation.
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  • 52
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    Angewandte Makromolekulare Chemie 192 (1991), S. 69-79 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Es wird ein allgemeines numerisches Verfahren vorgestellt, um die Modifikation der Grundgleichung für hydrodynamische Schmierung, die von mit Polymeren versetzten Schmierölen mit scherabhängiger Viskosität erbracht wird, zu berechnen.Das Verfahren basiert auf dem verallgemeinerten Newtonschen Fileßmodell und erlaubt, alle Fileßregionen zwischen dem rein Newtonschen und dem Exponentialgesetzverhalten kontinuierlich zu behandeln. Die Ergebnisse zeigen, daß der Einfluß der scherspannungsabhängigen Viskosität durch eine dimensionslose Zahl vollkommen charakterisiert wird, nämlich U · τ*/h*, wobei U die relative Gleitgeschwindigkeit, h* die charakteristische Filmdicke und τ* die Relaxationszeit des Schmieröles darstellen.Als praktisches Beispiel wird die Anwendung des Verfahrens aufgezeigt, um den Einfluß des Molekulargewichts und der Konzentration der Polymerkomponente des Schmieröls auf die hydrodynamische Schmierung zu bestimmen. Dieser Einfluß ist durch die starke Beziehung zwischen Polymereigenschaften und τ* verursacht.
    Notes: A general numerical procedure is presented to calculate the modification of the basic equation for hydrodynamic lubrication brought about by the use of polymeric fluids with shear depending viscosity. The procedure is based on the generalized Newtonian fluid model and allows to treat continuously all the flow regions between the pure Newtonian and the power law behavior. The results show that the influence of the viscosity depending on shear stress is completely characterized by one dimensionless number, namely U.·τ*/h*, where U is the relative sliding velocity, h* is the characteristic film thickness, and τ* is a characteristic time of the lubricant. The procedure is exemplified by applying it for the determination of the influence of the molecular weight and concentration of the polymeric component of the lubricant on the hydrodynamic lubrication. This influence is brought about by the strong relation between the polymer properties and τ*.
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  • 53
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    Angewandte Makromolekulare Chemie 192 (1991), S. 57-67 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Morphologien von spritzgegossenem und formgepreßtem Poly(1-buten) (PB-1) wurden im Polarisationsmikroskop und im Transmissionselektronenmikroskop untersucht. Eine dünne Oberflächenhaut und bis in den Kern der Probekörper reichende abgeplattet-sphärolithische Strukturen werden bei spritzgegossenem PB-1 beobachtet, während in formgepreßtem PB-1 typische Sphärolithe vorliegen. Das Bruchbild des spritzgegossenen PB-1 zeigt unter der Oberflächenhaut viele aufgereihte streifenartige Hohlräume, die senkrecht zur Spritzrichtung zur Mitte des Probekörpers wachsen. Aus diesen Beobachtungen kann geschlossen werden, daß eine beim Spritzgießen durch den Schmelzefluß induzierte Scherspannung nicht nur die Entstehung der Oberflächenhaut verursacht, sondern auch bis in die Mitte des Probekörpers hinein die Bildung abgeplatteter Sphärolithe bewirkt. Diese abgeplattet-sphärolithischen Strukturen sind für die beim Dehnen des spritzgegossenen PB-1 entstehenden, streifenartigen Hohlräume verantwortlich, während die Oberflächenhaut und die abgeplatteten Sphärolithe im Kern die Sprödigkeit und die im Vergleich zu formgepreßtem PB-1 geringere Bruchdehnung bewirken. Diese kann durch Tempern oberhalb des Schmelzpunktes erhöht werden.
    Notes: The injection-molded poly(1-butene) (PB-1) is found to be more brittle than the compression-molded PB-1. The morphologies of these specimens are examined by use of polarized optical microscopy and scanning electron microscopy (SEM). A skin layer and an oblate spherulitic structure extended to the core region are observed in the injection-molded PB-1, while typical spherulites exist in the compression-molded PB-1. Below the skin layer of the injection-molded PB-1, the fracture surface is found to consist of many aligned strip-like voids with ribbon edges propagating to the center of the specimen and perpendicular to the flow direction of injection-molding. Based on these observations, it can be inferred that shear stress induced by the melt flow during the injection-molding does not only cause the formation of skin layer, but also penetrates deeply into the central region of the injection-molded specimen causing the formation of oblate spherulites. The oblate spherulitic structure is responsible for the aligned voids during elongation of PB-1, while the existence of the skin layer and the oblate spherulites in core region is responsible for the brittleness of the injection-molded PB-1. The elongation of the injection-molded PB-1 is found to be lower than that of the compression-molded. This can be attributed not only to the presence of the skin layer but also to the oblate spherulites in the core region. The elongation can be improved by annealing at a temperature above the melting point of PB-1.
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  • 54
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The influence of linearly and circularly polarized light on the state of order of nematic dye-copolymers is investigated. For a nematic model system we have shown that the optical axis of these systems can be reorientated with linearly polarized light in a well defined manner. Furthermore these investigations prove that the isomerisation cycles of the azo dye is responsible for the described properties. By selection of circularly polarized light the same transmission behaviour as shown by selectively reflecting materials, i. e. cholesteric liquid crystals, was observed.
    Notes: Untersucht wird der Einfluß von linear und zirkular polarisiertem Licht auf den Ordnungszustand von nematischen Farbstoff- Copolymeren. Am Beispiel eines Modellsystems wird gezeigt, daß mit linear polarisiertem Licht die optische Vorzugsachse dieser Systeme gezielt reorientiert werden kann. Die Untersuchungen zeigen, daß der Isomerisierungszyklus des Azofarbstoffes für diese Eigenschaft des Materials verantwortlich ist Nach Bestrahlen der Probe mit zirkular polarisiertem Licht wird für das Polymere das gleiche Transmissionsverhalten beobachtet. Wie es auch selektivreflektierende Materialien, z. B. cholesterische Flüssigkristalle, aufweisen.
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  • 55
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    Keywords: Chemistry ; Polymer and Materials Science
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    Topics: Chemistry and Pharmacology , Physics
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  • 56
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: For fabricating microstructures with extreme structural heights a technology has been developed which is based on deep-etch lithography and subsequent replication processes. A particularly high precision is achieved if the lithographic process is carried out by means of synchrotron radiation. Electroforming and molding processes are used for the replication of microstructures from a large variety of materials. The field of application comprises micromechanics, microoptics, electrical and optical microconnectors as well as sensors and actuators.
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  • 57
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
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  • 58
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    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Charge carrier transport properties of organic polymers can vary over a wide range. The paper shows that the electron- and hole mobilities of polymers with pendant photoconductive groups (i. e. carbazole) are on the order of 10-6 cm2/Vs. In these materials the flow of electronic charge is maintained by the overlap of the π-orbitals of the pendant molecular groups. The large variation of this short-range interaction, depending on the local configurations encountered in polymer glasses, leads to a large variation of hopping probabilities and, hence, to wide rate-distributions. These distributions are reflected in the slow algebraic decay characteristics of the observed photocurrents. The typical time exponents α (α 〈 1) are shown to carry a great deal of physical information, if the dynamical range of the experiments is sufficiently large. The paper also refers to quasi-conjugated polymers (polysilanes) whose dynamic transport parameters are about 103 times better (faster) as compared to polymers with pendant groups. These new materials open interesting aspects for the development of new polymeric materials with better transport parameters and, hence, shorter 'switching times'.
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  • 59
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    Angewandte Makromolekulare Chemie 192 (1991), S. 103-111 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Durch Kondensation von p-Xylol mit Chloracetylchloride, 1,2-Dichlorethan und Dichlormethan mit Aluminiumtrichlorid in Schwefelkohlenstoff wurden Polyketone hergestellt und IR-spektroskopisch sowie bezuglich des Molekulargewichtes charakterisiert. Die thermischen Eigenschaften wurden thermogravimetrisch und mittels DSC untersucht. Die Prüfung der Harze auf ihre biologische Aktivität gegen Pseudomonas fluorescens, Bacillus subtilis and Aspergillus niger ergab, daß deren Wachstum durch die Polyketonharze kontrolliert werden kann.
    Notes: Some polyketones were prepared from p-xylene, chloroacetylchloride, 1,2-dichloroethane and dichloromethane using anhydrous aluminiumtrichloride and carbon disulfide as solvent. The resins thus obtained have been characterized by IR spectra and number average molecular weight. The thermal properties have been studied by thermogravimetry and differential scanning calorimetry. All the resins were tested for their biological activity against Pseudomonas fluorescens, Bacillus subtilis and Aspergillus niger. The results show that the growth of the tested organisms can be controlled by the polyketone resins.
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  • 60
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    Angewandte Makromolekulare Chemie 192 (1991), S. 145-153 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: In der Arbeit wurde die homogene Polyaddition von Pyromellitsäuredianhydrid und 4,4′-Diaminodiphenylmethan untersucht. Die Abhängigkeit des zahlenmittleren Molekulargewichts (M̄n) von der Zeit weist ein Maximum auf. Die Ursache der niedrigen Gleichgewichtswerte von M̄n beruht auf einer durch Wasserspuren im Lösungsmittel verursachten Dianhydridhydrolyse und damit einer gestörten Äquimolarität der funktionellen Gruppen. Im Laufe der Stabilisierung des M̄n-Gleichgewichtswertes entsteht auch die wahrscheinlichste Molmassenverteilung.
    Notes: The homogeneous polyaddition reaction of pyromellitic dianhydride with 4,4′-diaminodiphenylmethane was investigated. The dependence of the number average molecular weights on time has a maximum; low equilibrium values of M̄n are caused by a disturbed equimolarity of functional groups due to the hydrolysis of dianhydride with water present in the solvent. In the course of establishment of the equilibrium M̄n value, the molecular weight distribution changes to the most probable value.
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  • 61
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    Angewandte Makromolekulare Chemie 192 (1991), S. 133-144 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Das Phasen- und Mischbarkeitsverhalten der binären und ternären Polymermischungen von Polyarylat (PAR), Phenoxid und Poly(butylenterephthalat) (PBT) wurde untersucht. Die Mischungen wurden durch Ausfällen aus gemeinsamen Lösungen hergestellt, und die Mischbarkeit wurde durch DSC-Messungen und Transparenz der Schmelze beurteilt. Im Falle der binären Blends zeigten PAR/PBT und Phenoxid/PBT Mischbarkeit, während sich PAR/Phenoxid nicht mischen ließ. Die Mischbarkeitstendenz der unmischbaren PAR/Phenoxid-Mischungen konnte jedoch durch Zugabe von PBT erhöht werden; eine ausreichende Menge PBT machte die ternären Mischungen mischbar, so daß diese eine einzige Tg in der DSC-Kurve zeigten. Im ternären Phasendiagramm war das Maximum der Mischbarkeitsgrenze in Richtung auf die Phenoxidseite hin verschoben, was auf die bessere Mischbarkeit von PAR/PBT im Vergleich zu Phenoxid/PBT zurückgeführt wird.
    Notes: The phase and miscibility behavior of binary and ternary blends containing polyarylate (PAR), polyhydroxyether of bisphenol AIUPAC: poly[oxy(2-hydroxytrimethylene)oxy-1,4-phenylene-isopropylidene-1,4-phenylene]. (Phenoxy), and poly(butylene terephthalate) (PBT) were studied. The blends were prepared by solution-precipitation method and miscibility was examined by DSC and melt transparency. In binary blends, PAR/PBT and Phenoxy/PBT blends show miscibility, while PAR/Phenoxy appeared to be immiscible. However, the miscibility of incompatible PAR/Phenoxy blend was enhanced by addition of PBT. The addition of sufficient amount of PBT caused the ternary blend to have a single glass transition temperature. The shape of miscibility boundary of ternary blend was skewed to the apex of Phenoxy, which was attributed to the better miscibility of PAR/PBT than that of Phenoxy/PBT.
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  • 62
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Festphasen-Polykondensation von amorphen, unorientierten Poly(ethylenterephthalat)-Folien (PET) (Vorstufe der Du Pont Mylar® -Polyesterfilme), die mit einem speziellen Katalysator-und Monomer-System hergestellt wurden, war Gegenstand dieser Arbeit. Der Einfluß verschiedener Reaktionsparameter, wie Reaktionstemperatur und -zeit, auf die inhärente Viskosität (ηinh) und auf die Anzahl der Carboxy-und Hydroxy-Endgruppen wurde untersucht. Aus den Messungen von ηinh wurde eine empirische Gleichung erstellt, die die Berechnung von M̄n der PET-Folien nach der Festphasen-Polykondensation bei gegebener Zeit und Temperatur erlaubt. Das Schmelzverhalten verschiedener Festphasen-Polykondensate wurde ebenfalls untersucht.
    Notes: The solid-state polycondensation of poly(ethylene terephthalate) (PET) amorphous and unoriented films from Du Pont (precursor for their Mylar® Du Pont's registered trade mark for the polyester film. polyester film) prepared from a specified catalyst and monomer system has been studied. The effect of various reaction parameters such as reaction temperature and time on inherent viscosity (ηinh) and number of carboxy and hydroxy end-groups has been investigated. From ηinh measurements an empirical equation was taken which allows the calculation of (M̄n) of PET film after solid-state polycondensation at a certain temperature and time. The melting behaviour of the solid-state polycondensated samples was also studied.
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  • 63
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Sphärische makroporöse Partikel, die als Trägermaterialen für verschiedene Säulen-Operationen eingesetzt werden sollen, wurden mittels Suspensions- und Mikrosuspensionspolymerisation von Trimethylolpropan-trimethacrylat (TRIM) in Gegenwart verschiedener Mengen porogener Reagenzien (Toluol bzw. Mischungen von Toluol und Isooktan) hergestellt. Textur und Eigenschaften der Partikel variierten deutlich mit dem Anteil und der Zusammensetzung des porogenen Reagens und wurden zusätzlich durch die Wahl des Suspensionstabilisators beeinflußt. Die makroporösen Partikel wiesen ein Gesamtporenvolumen von 0,4 bis 3,6 cm3/g und eine spezifische Oberfläche von 7 bis 〉 450 m2/g auf. Alle Partikel enthielten Makroporen und, außer den Teilchen mit sehr niedriger spezifischer Oberfläche, einen gewissen Anteil an Mikroporen (Durchmesser 〈 60 Å). Durch Erniedrigung der Monomerkonzentration und Erhöhung des Isooktan-Gehaltes im porogenen Reagens auf 50 Gew.-% konnte das Auftreten von Mikroporen vollständig unterdrückt werden. Das Erhöhen des Isooktan-Gehaltes führte zu einem vergrößerten Gesamtporenvolumen und zu einem verringerten Quellvermögen der Polymermatrix in Toluol. Der Einfluß einer Hitzebehandlung bei 130°C und eines Aufpfropfens von Polymethylmethacrylat auf die Partikeleigenschaften wurde ebenfalls untersucht.Die Menge an nicht umgesetzten Doppelbindungen in den Partikeln konnte durch Variation der Polymerisationstemperatur verändert werden. Das Vorhandensein leicht zugänglicher Doppelbindungen ist wichtig, da sie zur Funktionalisierung der festen makroporösen Partikel verwendet werden können.
    Notes: Spherical macroporous particles, intended for use as carrier particles in various types of column operations, were prepared by suspension and microsuspension polymerization of trimethylolpropane trimethacrylate (TRIM), in the presence of various amounts of porogenic agents (toluene or mixtures of toluene and isooctane). The texture and properties of the particles varied markedly with the amount and composition of the porogenic agent, and were also affected by the choice of suspension stabilizer. Macroporous particles were prepared, ranging in total pore volume from 0.4 to 3.6 cm3/g, and in specific surface area from 7 to 〉450 m2/g. All of the particles contained macropores, and except for those with very low specific surface area, contained a certain fraction of micropores (diameter 〈60 Å). The presence of micropores could be eliminated completely by decreasing the monomer concentration and increasing the isooctane content of the porogenic agent to 50 wt.-%. Increasing the isooctane content also resulted in an increase in the total pore volume and a decrease in the tendency of the polymer matrix to swell in toluene. The effect on properties of particles by heat treatment at 130°C and by grafting poly(methyl methacrylate) onto the particles was also studied.The amount of unreacted double bonds of the particles could be varied by varying the polymerization temperature. The presence of easily accessible double bonds is important as they can be utilized for functionalization of the rigid macroporous particles.
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  • 64
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    Angewandte Makromolekulare Chemie 191 (1991), S. 31-38 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Eine einfache Methode für die Bestimmung der Grenzflächenhaftung in kurzfaserverstärkten Polymeren, beruhend auf der Längenverteilung von aus der Bruchfläche herausgezogenen Faserteilen, wurde entwickelt. Die Messungen mit Faserverbundwerkstoffen von isotaktischem Polypropylen mit 32 Gew.-% Kurzglasfasern bestätigen die Brauchbarkeit dieser Methode für eine empfindliche Beurteilung von Unterschieden in der Grenzflächenhaftung. Die Einflüsse von Temperatur, Polymer- und Glasfasermodifizierung sowie Faserorientierung auf die Grenzflächenhaftung wurden untersucht.
    Notes: For the evaluation of the interfacial adhesion in short-fibre composites, a simple method based on fibre pull-out length distribution was proposed. The experiments with three composites of isotactic polypropylene with 32 wt.-% of short-glass fibres confirm the potentials of the method for a sensitive determination of differences in the interfacial adhesion. The effects of temperature, crystallinity and fibre orientation angle on the interfacial adhesion were investigated.
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  • 65
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: PE und EPDM-Kautschuk wurden durch Aufpfropfen von Dibutylmaleat (DBM) mit Dicumylperoxid (DCP) als Initiator in Substanz im Temperaturbereich von 140-220°C funktionalisiert. Der Pfropfungsgrad wurde IR-spektroskopisch und durch DSC-Messungen ermittelt. Die für die Pfropfung optimalen DBM- und DCP-Konzentrationen betragen 0,5 bzw. 0,2 Gew.-%. Die Kinetik der Pfropfreaktion ist für PE und EPDM vergleichbar; die Aktivierungsenergien betragen ca. 145 bzw. 130 kJ/mol. Die Pfropfungsgrade sind für PE höher als für EPDM; bei PE/EPDM-Blends steigt der Pfropfungsgrad mit zunehmendem PE-Anteil. Ein Pfropfungsmechanismus, der Nebenreaktionen berucksichtigt, wird vorgeschlagen.
    Notes: Functionalization of polyethylene (PE) and ethylene propylene diene terpolymer (EPDM) in the bulk through dicumyl peroxide (DCP) initiated grafting of dibutyl maleate (DBM) has been studied in the temperature range from 140 to 200°C. The degree of grafting has been determined by infrared spectrophotometry and DSC. The concentration of DBM and DCP has been optimized. 0.5 wt.-% and 0.2 wt.-% DCP for PE and EPDM, respectively, and 10% DBM for both have been found to be the optimum. The kinetics of the grafting reaction is comparable for PE and EPDM. The activation energy of grafting is ca. 145 kJ/mol for PE and ca. 130 kJ/mol for EPDM. The influence of structure of polyolefins on the degree of grafting has also been studied. A higher degree of grafting is obtained for PE than for EPDM. For PE/EPDM blends, the degree of grafting increases with increasing PE content in the blends. A through discussion and proposed mechanism for grafting and other competitive secondary reactions has been provided.
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  • 66
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    Angewandte Makromolekulare Chemie 191 (1991), S. 71-80 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die dynamisch-mechanischen Eigenschaften von gehärteten Epoxidharzen, gefüllt mit porösen Siliciumdioxid-Mikrokugeln mit unterschiedlichen spezifischen Oberflächen, Porenradien, Porenvolumina und adsorbierter Wassermenge, wurde untersucht. Die Glasubergangstemperaturten (Tg) der Composite sind 12-14°C niedriger als die des ungefullten Harzes, was auf die bevorzugte Adsorption von Härter an den porösen Mikrokugeln zurückgeführt wird. Mit zunehmender adsorbierter Wassermenge steigt die Tg der Composite an. Der Speichermodul ist mit der mit Quecksilber bestimmten spezifischen Oberfläche (Hg-Oberfläche) der Mikrokugeln, die der Summe der Oberfläche von Poren mit einem Durchmesser größer als 4 nm entspricht, korreliert.Das Verbältnis tan δc/tan δm nimmt mit zunehmender Hg-Oberfläche ab.
    Notes: Dynamic mechanical properties were studied for epoxy resin filled with porous silica microballoons with varying surface area, pore radius, pore volume and adsorbed water. The glass transition temperature (Tg) of the composites is 12-14°C lower than the Tg of the unfilled epoxy resin. This Tg depression is attributed to the preferential adsorption of curing agents on the porous silica microballoons. Tg of the composite increases with increase in the adsorbed water on fillers. The storage modulus has a distinct correlation with the Hg-surface area of silica microballoons, which corresponds to the sum of the surface area of pores with radii larger than about 4 nm.Tan δc tan δm decreases with increasing Hg-surface area.
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  • 67
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Membranen aus Blends von Nylon 6 mit Poly(acrylsäure) (PAA) mit PAA-Gehalten zwischen 25 und 45 Gew.-% wurden durch Filmgießen hergestellt und anschließend durch Eintauchen in eine Aluminiumsalzlösung ionisch vernetzt. Die Glasübergangstemperaturen (Tg) der Membranen wurden mit der DSC-Methode bestimmt. Alle Proben zeigen eine einzige Tg oberhalb der Tg der Homopolymeren, die sich mit zunehmender Scanzeit verschiebt; dies wird auf die Eliminierung von Wasser und die Bildung von Anhydriden im nicht vernetzten PAA-Anteil zurückgeführt.Die Morphologie wurde rasterelektronenmikroskopisch untersucht; die Membranen zeigen eine dichte, porenfreie Struktur ohne Phasenseparation, was auf eine völlige Mischbarkeit der beiden Homopolymeren im untersuchten Zusammensensetzungsbereich schließen läßt. Die Festigkeit der Membranen liegt je nach PAA-Gehalt zwischen 5 und 26 MPa; Membranen mit hohem PAA-Anteil zeigen trotz höherer Vernetzungsdichte eine geringere Zugfestigkeit, was mit der geringen Festigkeit von PAA und der mit größerem PAA-Anteil zunehmenden Quellung zusammenhängt. Letztere wurde durch Messen der Wasseraufnahme trockener Membranen bestimmt; sie steigt von 23,6 Gew.-% bei einem PAA-Gehalt von 25 auf 76,3 Gew.-% bei einem PAA-Gehalt von 45 Gew.-%.
    Notes: Ionically crosslinked blended membranes were prepared from blends of nylon 6 and poly(acrylic acid) (PAA) with the proportion of PAA ranging from 25 to 45 wt.-%. The technique consists of casting a film of the blend, followed by drying and immersion in an aluminum salt crosslinking solution for a predetermined time. The glass transition temperature (Tg) of the membranes was determined by differential scanning calorimetry (DSC). All the samples exhibited a single Tg, which is higher than that of either polymer. There is also a shift in the Tg with increasing scanning time. This phenomenon is attributed to the elimination of water molecules and the formation of anhydrides in the non-crosslinked PAA portion of the membrane. The membrane morphology was studied using scanning electron microscopy (SEM) and shows a dense structure without any pores. No phase separation is observed by scanning cross-sections of the samples, indicating that nylon 6 and PAA are completely miscible in the ranges studied. The membrane material strength lies in the range of 5 to 26 MPa and varies with the amount of PAA in the membrane. Samples with higher PAA content show lower tensile strength in spite of increased crosslinking density. This is due to the inherent low strength of PAA, coupled with increasing swelling of the membrane with increasing PAA content. The latter is confirmed by the measurement of water uptake into a dry membrane which increases from 23.6% to 76.3% with the membrane PAA content increasing from 25 to 45 wt.%.
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  • 68
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    Angewandte Makromolekulare Chemie 191 (1991), S. 81-107 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Practically no adhesion is observed at the interface poly(tetrafluoroethylene)/glass fiber. We have investigated methods to improve adhesion between these interfaces. We have also discussed the question of possible reinforcement, i.e. increase of tensile strength and a simultaneous decrease of elongation.In this first part we present some calculations demonstrating the prerequisites for reinforcement using existing theoretical models. We describe the influence of modification of the glass fiber surface by dispersion coating or by plasma polymerization.In a second part the influence of polymer surface modification and of additives will be dealt with.
    Notes: In Mehrphasensystemen aus Poly(tetrafluorethylen) (PTFE) und Glasfasern besteht praktisch keine Haftung zwischen Matrix und Füllstoff. Es wurde der Frage nachgegangen, ob es Wege zur Verbesserung der Grenzflächenhaftfestigkeit gibt und ob diese Verbesserungen ausreichen, eine Verstärkung, d. h. Anhebung der Reißfestigkeit bei gleichzeitigem Rückgang der Dehnung des Gesamtsystems zu erzielen.In diesem ersten Teil wird den theoretischen Voraussetzungen und der Modifizierung der Füllstoffoberflächen mittels Dispersionsbeschichtungen sowie Plasmaätzen und Plasmapolymerisation nachgegangen.In einem zweiten Teil werden Möglichkeiten zur Verbesserung der Grenzflächenhaftung durch Modifizierung der Polymer-Oberfläche und durch Additive untersucht.
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  • 69
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    Angewandte Makromolekulare Chemie 191 (1991), S. 109-126 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Practically no adhesion is observed at the interphase of poly(tetrafluoroethylene)/glass fiber. We have investigated methods to improve this adhesion and discuss the influence of this improved adhesion on the mechancial properties of the multiphase system.In this paper the influence of a modified polymer surface and of additives is described.
    Notes: In Mehrphasensystemen aus Poly(tetrafluorethylen) (PTFE) und Glasfasern besteht praktisch keine Haftung zwischen Matrix und Füllstoff.Es wurde die Frage untersucht, ob es Methoden gibt, diese Grenzflächenhaftung zu erhöhen und welchen Einfluß diese Erhöhung auf die Eigenschaften des Verbundsystems hat.In dem hier vorliegenden Teil 2 wird speziell auf den Einfluß der Modifizierung der Polymeroberfläche und des Zusatzes von Additiven eingegangen.
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  • 70
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    Angewandte Makromolekulare Chemie 191 (1991), S. 127-144 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Due to the very strong variation of the viscosity of the reaction mass with increasing monomer conversion, three stationary states for the tubes of a multitubular system with cooling vessel can be found. As a consequence, a maldistribution of the fluid arises, so that the reactor stability and the polymer quality are negatively influenced. The recycling of the reaction mass is a helpful method to increase the reactor stability. In this paper some fundamental aspects of the use of multitubular reactors for the polymerization of styrene are studied.
    Notes: Infolge der sich mit steigendem Monomerumsatz stark verändernden Viskosität der Reaktionsmasse existieren im Multirohrreaktor mit Kühlung mindestens drei stationaäre Punkte bezüglich des Einzelrohrmassenstromes gleichzeitig. Als Konsequenz ergibt sich eine Ungleichverteilung der Rohrbelastung, die sowohl die Reaktorstabilität als auch die Polymerqualität negativ beeinflußt. Das Betreiben einer Rückführung kann das Reaktorverhalten stabilisieren. In der vorgelegten Arbeit werden einige fundamentale Aspekte der Anwendung von Multirohrreaktoren für die Massepolymerisation von Styrol untersucht.
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  • 71
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    Angewandte Makromolekulare Chemie 191 (1991), S. 171-176 
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die nucleophile Substitution von verschieden substituierten Phenoxygruppen in Polyphenylacrylaten durch Ethanolamin in Dioxan wurde bei 60, 80 und 100°C untersucht. Der Umsatz wurde IR- und 1H-NMR-spektroskopisch und elementaranalytisch bestimmt; er hängt sowohl von der Temperatur als auch von der Art der Substituenten am Phenylring ab.
    Notes: The nucleophilic substitution reaction of differently substituted phenoxy groups with ethanolamine in various poly(phenyl acrylate)s was investigated in dioxane at 60, 80, and 100°C. The conversion, as determined from IR- and 1H-NMR spectroscopy and elemental analysis, depends on the temperature and the kind of substituents at the phenyl ring.
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  • 72
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: All of the coat proteins of the sporozoite and merozoite stages of Plasmodium, determined to date, contain tandem repeats and most of these contain at least one proline residue. These tandemly repeated segments of the circumsporozite (CS) proteins of P. falciparum and P. knowlesi have been shown to constitute an immunodominant epitope. Antibodies to these peptide segments have been shown to be protective and cause the shedding of the CS protein, known as the CSP reaction. In this study, four synthetic peptides were prepared by solid-phase peptide synthesis. The first peptide corresponds to the tetrapeptide tandem repeat in the CS protein of P. falciparum, repeated eight times, (NANP)8. The second peptide is an analogue of the first in which glycine is substituted for proline, (NANG)8. The third peptide corresponds to the tandem repeat of P. knowlesi, PK(1-24), which is repeated twice (QAQGDGANAGQP)2. The fourth peptide is a tetrapeptide repeat, corresponding to the C-terminal tetrapeptide of PK(1-24) and is repeated eight times, (AGQP)8. It is shown by CD measurements that the presence of proline in these repeats induces an increase in β-sheet (β-turn) content in the (NANP)8 peptide relative to the repeat of (NANG)8 and PK(1-24) peptide in aqueous media. The (AGQP)8 peptide has the highest β-sheet (β-turn) content in the synthetic peptides. It is concluded that this increase in defined structure correlates well with and hence may contribute to the increased antigenicity in these repeats.
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  • 73
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Self-assembling chemotherapeutic agents are mixtures of relatively nontoxic precursors that can combine chemically under physiological conditions to form products with greater cytotoxic and/or antimicrobial activity than either of the precursors. Combinations that form products more rapidly in or near the target (tumor, pathogen, virally infected cell) than in normal tissues will exhibit target-selective synergism, thus exhibiting an antitarget selectivity that is greater than the selectivities of the product (e.g., a hydrazone) and of either precursor (e.g., a hydrazine derivative or ketone) used singly.This paper describes the target-selective cytotoxic synergism of a cationic aldehyde (A) and a cationic acylhydrazine (B) containing a triarylalkylphophonium moiety against Ehrlich ascites carcinoma cells (ELA) in culture, in addition to reviewing previous work on self-assembling cytotoxins. The synergism between A and B is carcinoma selective when the ELA cells (the target) are compared to CV-1, A, B and the hydrazone C resulting from their reaction are lipophilic delocalized cations that selectively inhibit ELA growth relative to CV-1 growth. The hydrazone C is more growth inhibitory than either A or B for both cell lines. A combination of A with an unreactive analogue of B and a combination of B with an unreactive analogue of A did not synergistically inhibit ELA proliferation. The degree of synergism is greater against the ELA cells than against the CV-1 cells. These data, together with hydrazone formation kinetics, suggest that A and B are both concentrated together selectively inside the ELA due to the transmembrane potentials, reacting inside the ELA cells at a higher velocity than inside the CV-1 cells to form the more growth-inhibitory hydrazone C.
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  • 74
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    Biopolymers 29 (1990) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 75
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclic pentapeptides are excellent models for reverse turns and have been used extensively in our laboratory to explore the influence of different amino acid sequences on turn preference. This paper is divided into two parts: In the first, we review our previous studies of cyclic pentapeptides. We summarize work that demonstrates the range of conformations possible within the cyclic pentapeptide backbone, the importance of sequence chirality in determining the backbone fold, and the utility of these cyclic pentapeptides as models for various turns. In the second, we present new results on two cyclic pentapeptides that contain β-turns with Pro-Ala or Pro-Asn sequences in the i + 1 and i + 2 positions. By stereochemical criteria, a type I β-turn is expected to be preferred by such L-L sequences. On the other hand, in proteins Asn occurs frequently in the i + 2 position of type II turns. We asked whether the same propensity would be manifest in an isolated model peptide, and if so, what the interactions were that influenced the relative stability of the type I and type II turns. To address these questions we have compared the conformational behavior of two peptides: cyclo(Gly-Pro-Ala-D-Phe-Pro) and cyclo(D-Ala-Pro-Asn-Gly-Pro). From previous studies, we anticipated that both peptides would contain an inverse γ-turn and a β-turn which consisted of either Gly-Pro-Ala-D-Phe or D-Ala-Pro-Asn-Gly in positions i to i + 3, respectively. Nuclear magnetic resonance analysis confirms this overall backbone conformation. Furthermore, quantitative nuclear Overhauser effect measurements in combination with molecular dynamics simulations and torsionally-forced energy minimizations have enabled us to determine that both type I and type II β-turns are present in equilibrium in these peptides. The introduction of Asn in position i + 2 shifts this equilibrium significantly towards type II. We have done preliminary assessment of the possible side-chain/backbone conformations that contribute to the shift in populations.
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  • 76
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    Biopolymers 29 (1990), S. 289-299 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To better understand the structural basis of protein-DNA interactions, the conformational changes that accompany these interactions need to be described. In order to develop a methodological approach to this problem, Fourier transform infrared spectroscopy (FTIR) with derivative resolution enhancement has been used to identify conformational changes that occur when a 29-residue synthetic peptide binds nonspecifically to heterogenous cellular DNA in aqueous solution. The peptide sequence was chosen de novo, in order to rationally design a peptide model that would allow the relationship between DNA binding and the stability of protein secondary structure to be studied. Peptide at a concentration of 100-200 μM produces 50% saturation of heterogenous phage DNA sequences as well as of short synthetic oligonucleotides. FTIR spectra reveal significant changes in peptide and DNA upon binding. Second-derivative spectra resolve the amide I band of native peptide into components located at 1627 (β-strand), 1658 (α-helix), and 1681 (turn or β-strand) cm-1, with a distinct shoulder at 1647 cm-1 (disordered structure). Assignment of the 1681 cm-1 vibration to a turn conformation is supported by uv CD studies, which indicate significant amounts of turn structure in unbound peptide. Ultraviolet CD also confirms the existence of disordered and β-strand regions in the free peptide. Upon interacting with DNA the band at 1681 cm-1 (turn) is no longer seen; a new band appears at 1675 cm-1; the 1627 cm-1 band (β-strand) is considerably reduced in intensity; the position of the α-helical (1658 cm-1) component remains unchanged; the shoulder at 1647 cm-1 (disorder) disappears. The new vibration at 1675 cm-1 is characteristic of β-strand structures. The asymmetric stretch (vAS) of the DNA phosphates shifts from 1223 (unbound) to 1229 cm-1 (bound); the relative intensities of νAS and the PO2- symmetric stretch (vs) are altered upon peptide binding. The data is consistent with the following conclusions: (a)DNA binding changes the secondary structure of the peptide, (b) disordered region(s) are only observed in free peptide, i.e., DNA binding stabilizes and increases order in the peptide secondary structure, (c) turn(s) change into β-strand and/or α-helical conformations(s) when peptide binds to DNA, (d) a β-strand conformation that is characterized bya 1627 cm-1 vibration is present in free and bound peptide, (e) there is a particular β-strand vibration/conformation that is only present in the bound peptide, (f) an α-helical region exists in both free and bound peptide, (g) DNA remains in a B-family conformation upon peptide binding, and (h) DNA phosphates participate in peptide binding and/or subtle changes occur in the DNA conformation upon complex formation.
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  • 77
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    Biopolymers 29 (1990) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 78
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Previous studies have demonstrated that His 12 plays a major role in the pH-dependent stability of the helix formed by the isolated C-peptide (residues 1-13 of ribonuclease A). Here, amino acid replacement experiments show that His 12+ stabilizes the C-peptide helix chiefly by interacting with Phe 8. The Phe 8 ⃛ His 12+ ring interaction is specific for the protonated form of His 12 (His 12+) and the interaction is not screened significantly by NaCl, unlike the charged group ⃛ helix dipole interactions studied earlier in C-peptide. Analogs of C-peptide that are unable to form the Phe 8 ⃛ His 12+ interaction show large increases in helix content for Phe → Ala and His → Ala. Therefore, the helical tendencies of the individual residues Phe, His, and Ala are important in determining the result of a replacement experiment. Since the side chains of Phe 8 and His 12 probably interact within the N-terminal helix of ribonuclease A, the existence of the Phe 8 ⃛ His 12+ interaction in the isolated C-peptide helix adds to the evidence that the C-peptide helix is an autonomous folding unit.
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  • 79
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthetic RNA poly[r(A-T)] has been synthesized and its CD spectral properties compared to those of poly[r(A-U)], poly[d(A-T)], and poly[d(A-U)] in various salt and ethanolic solutions. The CD spectra of poly[r(A-T)] in an aqueous buffer and of poly[d(A-T)] in 70.8% v/v ethanol are very similar, suggesting that they both adopt the same A conformation. On the other hand, the CD spectra of poly[r(A-T)] and of poly[r(A-U)] differ in aqueous, and even more so in ethanolic, solutions. We have recently observed a two-state salt-induced isomerization of poly[r(A-U)] into chiral condensates, perhaps of Z-RNA [M. Vorlíčková, J. Kypr, and T. M. Jovin, (1988) Biopolymers 27, 351-354]. It is shown here that poly[r(A-T)] does not undergo this isomerization. Both the changes in secondary structure and tendency to aggregation are different for poly[r(A-T)] and poly[r(A-U)] in aqueous salt solutions. In most cases, the CD spectrum of poly[r(A-U)] shows little modification of its CD spectrum unless the polymer denatures or aggregates, whereas poly[r(A-T)] displays noncooperative alterations in its CD spectrum and a reduced tendency to aggregation. At high NaCl concentrations, poly[r(A-T)] and poly[r(A-U)] condense into ψ (-) and ψ (+) structures, respectively, indicating that the type of aggregation is dictated by the polynucleotide chemical structure and the corresponding differences in conformational properties.
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  • 80
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    Biopolymers 29 (1990), S. 393-405 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Tm of internal loop-forming (dA · dT)N domains in pBR322 DNA has been measured over a tenfold range of [Na+]. The slopes SN = dTm/d log[Na+] are linear and decrease in magnitude with decreasing loop size N, signaling a reduction in Na+ released during the transition of these domains to the coil state. Values of SN decrese linearly with increasing N-1 in accordance with the expectation of a simple model for the occurrence of a gradient of long-range electrostatic forces at helix-coil boundaries, and extrapolate almost precisely to the value of S∞ observed for (dA · dT)∞. These results indicate (1) less counterion is released per phosphate residue from the finite loop than from the infinitesized loop, and (2) the difference in binding is constant for each boundary formed and independent of the size of the loop within the range examined: ∼ 350 base pair (bp) 〉 N 〉 71 bp. The slope of the dependence of SN on N-1 indicates the region of higher charge density at the boundary extends at least 18 Å into the coil and probably 40-50 Å before dropping to a value characteristic of the unperturbed coil. The free energy for excess counterion binding at boundaries can be expressed by \documentclass{article}\pagestyle{empty}\begin{document}$$ {{ - \Delta G} \mathord{\left/ {\vphantom {{ - \Delta G} {RT}}} \right. \kern-\nulldelimiterspace} {RT}} = 10.47{\rm log}\left[{{\rm Na}^ + } \right] + 5.234 $$\end{document} When the loop entropy function in a statistical mechanical algorithm for the dissociation of DNA is weighted by this quantity, calculated Tm are seen to vary by only ±0.09°C from observed.
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  • 81
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel thyrotropin-releasing hormone (TRH) analogue, [2, 4-MePro3]-TRH (2, 4-MePro: 2-carboxy-2, 4-methanopyrrolidine), has been synthesized using a rapid solid phase peptide synthesis method, and its conformational properties investigated by one- and two- dimensional (2D) nmr spectroscopy and by proton Overhauser measurements. Following a published approach, calibrated interproton Overhauser effects were used together with distance geometry analysis to deduce that the single conformation of the His-2, 4-MePro tertiary amide bond is trans in aqueous solution. This conclusion was corroborated by 2D dipolar-correlated (NOESY) spectroscopy. A preferentially extended conformation is indicated by the nmr data, similar to that of TRH. The φ, ψ conformational space of 2, 4-MePro is, however, significantly different from that of trans proline and the structural consequences of these differences at the C-terminus are discussed. The distribution of histidine side-chain conformation in the TRH analogue was deduced from coupling constants and from the short-range interaction between the imidazole ring and one of the prochiral faces of the 2, 4-MePro side chain.
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  • 82
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effects of calcium ions on the solution properties of porcine submaxillary mucin (PSM) have been investigated by static and dynamic light scattering. The weight average molecular weights of PSM fractions are unaffected by the addition of up to 0.5M CaCl2: these data are within experimental error of those for solutions in 0.1M NaCl. The distribution of relaxation frequencies derived from the dynamic data shows the existence of two distinct relaxation modes. The average relaxation times have been interpreted to yield the z-average translational diffusion coefficient and the longest intramolecular relaxation time τ1. A plot of τ1 vs 〈1/Rh〉z-3 is linear, and consistent with plots of such data recorded for PSM in 0.1M NaCl and 6M GdnHCl solutions. However, the τ1 values and the associated results for 〈Rh-1〉z-1 in 0.5M CaCl2 are smaller than those determined in 0.1M NaCl. This suggests that the conformation of PSM in CaCl2 solution is more contracted than those in the other two solvents. These results are consistent with the compact packaging of mucin in the secretary granules that have elevated Ca2+ levels.
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  • 83
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    Biopolymers 29 (1990), S. 449-459 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calorimetric titrations have been performed on the binding of ethidium and propidium to calf thymus DNA at temperatures in the 15-60°C range. Enthalpy changes (ΔHB) derived from these experiments performed with the new Omega reaction calorimeter have a precision of ±0.10 kcal/mol or less at all temperatures. For ethidium (a monocation), ΔHB varies little with temperature, and the heat capacity change (ΔCP) for the binding reaction derived from these parameters is 10 cal/deg/mol. In contrast, ΔHB changes from -6.5 to -8.1 kcal/mol for DNA binding of propidium (a dication due to a charged amine group at the end of an alkyl chain attached to the phenanthridine ring nitrogen), and ΔCP is -57 cal/deg/mol. At 21°C a plot of ΔHB vs mole ratio is curved downward for propidium in the 0.08-0.25 range, whereas the same plot at 45°C is a straight line from 0.05 to 0.15 and sharply downward thereafter. Similar plots for ethidium follow the latter pattern between 25 and 50°C. These observations and our analyses of ΔHB and ΔSB are consistent with the hypothesis that the location in the DNA complex and the rotational motion of the alkylamine chain change substantially over the temperature range in this study. Only near 50°C is ΔHB equal for the binding of these two cations to DNA, and caution must be used in analyses of enthalpic effects when the temperature dependence for ΔHB is not available.
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  • 84
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The triphenylethylene antiestrogen trans-tamoxifen is an effective antitumor agent used in the treatment of human breast cancer. While the antiestrogenic activity of trans-tamoxifen clearly plays an important role in its tumoricidal action, some of the biological effects of trans-tamoxifen are independent of estrogen. Therapeutic concentrations of trans-tamoxifen inhibit protein kinase C (PKC) and calmodulin-dependent enzymes. PKC and calmodulin play critical roles in growth regulation, and there is evidence that inhibition of PKC and calmodulin by trans-tamoxifen may contribute to the antiumor activity of the drug in vivo.The geometric isomers cis- and trans-tamoxifen have a number of opposing biological activities that have been attributed to their interactions with the estrogen receptor, Cis-tamoxifen is generally estrogenic, whereas trans-tamoxifen is generally antiestrogenic. In this report, we compared the effects of cis- and trans-tamoxifen on PKC activity and on calmodulin-dependent cAMP phosphodiesterase activity. Cis- and trans-tamoxifen inhibited the Ca2+- and phosphatidylserine- (PS-) dependent activity of purified rat brain PKC with indistinguishable potencies, but cis-tamoxifen was somewhat more potent than the trans isomer in the inhibition of the Ca2+- and PS-independent activity of PKC. In addition, cis-tamoxifen was the more potent isomer in the inhibition of T lymphocyte activation, an event that entails a PKC-requiring signal transduction pathway. A modest preference of the cis isomer was also observed in the inhibition of a calmodulin-dependent cAMP phosphodiesterase. These results suggest a congruence between triphenylethylene binding sites on PKC and on the activated calmodulin-cAMP phosphodiesterase complex. We conclude that the interactions of cis- and trans-tamoxifen with PKC and the activated calmodulin-cAMP phosphodiesterase complex offer a criterion for distinguishing biological effects of triphenylethylenes that are due to interactions with the estrogen receptor from the biological effects resulting from their inhibitory activities against PKC and calmodulin-dependent processes.
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  • 85
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A peptide affinity inactivator, Ac-Leu-Arg-Arg-Ala-(BrAc)Orn-Leu-Gly, was used as a tool to probe for active site residues in the catalytic subunit of bovine cAMP-dependent protein kinase. The peptide inactivated the catalytic subunit in an active site-directed and monophasic manner with a first-order rate constant of 0.03 min-1 and a dissociation constant of 675 μM. Studies with radioactive peptide indicated that approximately one equivalent of peptide was incorporated into each protein molecule. Protein sequencing identified the modified residue as Cys-199. A possible location for Cys-199 within the active site is suggested.
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  • 86
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The alkaline phosphatase signal peptide participates in transport of the enzyme to the periplasmic space of Escherichia coli. The signal sequence, like that of other signal peptides, is composed of a polar amino-terminal segment, a central region rich in hydrophobic residues and a carboxy-terminal region recognized by signal peptidase. We have previously shown that an alkaline phosphatase signal peptide mutant containing a polyeucine core region functions efficiently in transport of the enzyme [D. A. Kendall, S. C. Bock, and E. T. Kaiser (1986) Nature 321, 706-708]. In this study, some of the amino acid changes involved in the polyleucine sequence are examined individually. A Phe to Leu substitution as the sole change results in impaired transport properties in contrast to when it is combined with three other amino acid changes in the polyleucine-containing sequence. A mutant with a Pro to Leu substitution in the hydrophobic core region is comparable to wild type while the same type of substitution (Pro to Leu) in the carboxy-terminal segment results in substantial accumulation of the mutant precursor. Finally, introduction of a basic residue into the hydrophobic segment (Leu to Arg substitution) results in a complete export block. These results exemplify the spectrum of properties produced by individual residue changes and suggest there is some interplay between hydrophobicity and conformation for signal peptide function.
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  • 87
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    Biopolymers 29 (1990), S. 171-177 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A search for highly amphiphilic α-helices has been made in a data base of protein sequences, using the helical hydrophobic moment as a criterion of amphiphilicity. The protein segments of largest hydrophobic moment have been analyzed. For the segments whose structures are known, they are in fact α-helices. Two of the segments having very large hydrophobic moments are from the smaller C-terminal portion of the human immunodeficiency virus (HIV) envelope glycoprotein gp41. Also, among segments having large hydrophobic moments, but not among the most extreme, are lytic peptides such as melittin. Melittin seeks surfaces between polar and apolar phases, including the membrane-water interface. It is conceivable that the gp41 segments of extreme hydrophobic moment may participate in one of the membrane-related functions of the HIV virus.
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  • 88
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    Biopolymers 29 (1990), S. 179-196 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To examine the importance of the aromatic side chains of enkephalin on opiate activity, we report the synthesis and conformational analysis of a series of analogues related to enkephalin with β-naphthylalanine in place of phenylalanine at the fourth position. Three linear analogues (Tyr-D-Ala-Gly-(L and D)-β Nal(1)-Leu-NH2 and Tyr-D-Ala-Gly-β Nal(2)-Leu-NH2) were initially synthesized to examine the effect of the substitution on biological activity. The increased activity of these peptides at the μ-opiate receptor, compared to native Leu-enkephalin, prompted us to examine the more conformational constrained analogues, Tr-c[D-A2bu-Gly-(L and D)-β Nal(1)-Leu], incorporating a α,γ-diaminobutyric acid at the second position and cyclization to the carboxylic end of the leucine. These two cyclic analogues provide insight into the necessity for the L chirality of the aromatic residue at position 4. The Tyr-c[D-A2bu-Gly-L-β Nal(1)-Leu] analogue is highly potent and displays a slight preference for the μ receptor. The conformational analysis indicates that despite the high flexibility of the tyrosine side chain, the aromatic rings of the tyrosine and naphthylalanine are relatively distant from each other. The presence of two intramolecular hydrogen bonds help maintain the conformation of the 14-membered backbone ring that keeps the side chains directed away from each other. These findings are in agreement with our model of an extended structure required for μ selectivity and a folded form with close aromatic ring placement for δ selectivity.
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  • 89
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    Biopolymers 29 (1990) 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 90
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C off-resonance rotating frame spin-lattice relaxation technique is applicable to the study of protien rotational diffusion behaviour in a variety of experimental situations. The original formalism of James and co-workers (1978) (J. Amer. Chem. Soc. 100, 3590-3594) was constrained by the assumption of random isotropic reorientational motion. Here we include in the formalism anisotropic tumbling, and present the results of computer simulations illustrating the differences between anisotropic and isotropic reorientational motion for the off-resonance rotating frame spin-lattice relaxation experiment. In addition, We have included chemical shift anisotropy of the peptide carbonyl carbon as an additional relaxation mechanism contribution, to permit high field nmr protein rotational diffusion measurements.
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  • 91
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    Biopolymers 29 (1990), S. 481-489 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Binding of chromomycin A3 (CRA) to calf thymas DNA was investigated in the presence of divalent cations using visible absorption and 1H-nmr spectroscopies. An apparent equilibrium binding constant (∼ 1011M-1) was obtained from metal competition experiments using EDTA to remove the metal cation from the DNA-M-CRA (M: metal) complex. The large binding constant of the drug to DNA enabled us to obtain essentially complete complexation of CRA to the short homogeneous d(ATGCAT)2 duplex using stoichiometric amounts of the metal cation. Large induced chemical shifts were observed in the 1H-nmr spectrum of the above complex using the paramagnetic Co2+ cation indicating that the metal occupies a unique binding site. Since no induced 1H-nmr chemical shifts were observed for the drug-Co2+ mixture, it was concluded that no metal-drug complex is formed. In addition, it was found that bound CRA is negatively charged at physiological pH and binding to the DNA could be affected only by using metal cations whose ionic radius size (〈 0.85 Å) and charge (2+) were simultaneously satisfied. Stringent metal cation selectivity for the DNA-M-CRA complex may be intimately connected with the antitumor selectivity of CRA, since different types of cells generally possess widely differing molar concentrations of metal cations.
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  • 92
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C off-resonance rotating frame spin-lattice relaxation technique is applicable to the study of protein rotational diffusion behavior in both model in vitro and in vivo systems. The original formalism of James and co-workers [(1978) J. Am. Chem. Soc. 100, 3590-3594] was constrained by the assumption of random isotropic reorientational motion of a monodisperse protein population. Here we extend the formalism to include polydispersity. Application is made to the alkaline pH induced association of lysozyme, lysozyme-bovine serum albumin mixtures, and to the phase separation of lysozyme salt-water mixtures induced by low temperature.
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  • 93
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular dynamics simulations on the sequence d(CGCGAATTCGCG)2 have been carried out using both united atom and all-atom representations, and starting the simulations both from a regular repeating B-DNA structure and from the x-ray single crystal B-DNA structure. An all-atom B-DNA simulation on the sequence d(GCGCGCGCGC)2 has also been carried out, in order to compare it with a previous united atom simulation. The helix repeats, H-bonding, sugar pucker profiles, and average torsional angles are all in the range observed in crystallographic and nmr studies for B-DNA helices. In some of the sequences, there is a significant bend in the DNA helices. The individual helix repeats, with focus on 3′CpG5′ and 3′GpC5′ units, show the opposite helix repeat to that suggested by Calladine's rules.
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  • 94
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    Biopolymers 29 (1990), S. 509-515 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The peptide N-Boc-L-Pro-dehydro-Phe-L-Gly-OH was synthesized by the usual workup procedure and finally coupling the N-Boc-L-Pro-dehydro-Phe to glycine. The peptide crystallizes in monoclinic space group P21 with a = 8.951(4) Å, b = 5.677 (6) Å, c = 21.192(11) Å, β = 96.97(4)°, V = 1069(1) Å3, Z = 2, dm = 1.295(5) Mgm-3, and dc = 1.297(4) Mgm-3. The structure was determined by direct methods using SHELXS86. The structure was refined by the block-diagonal least-squares procedure to an R value of 0.074 for 1002 observed reflections. The C2α-C2β distance of 1.33(2) Å is an appropriate double bond length. The angle C2α-C2β-C2γ is 133(1)°. The peptide backbone torsion angles are θ1 = -167(1)°, ω0 = 179(1)°, φ1 = -48(1)°, ψ1 = 137(1)°, ω1 = 175(1)°, φ2 = 65(2)°, ψ2 = 15(2)°, ω2 = -179(1)°, and φ3 = -166(1)°. These values show that the Boc group has a trans-trans conformation while the peptide backbone adopts a β-turn II conformation, which is stablized by an intramolecular hydrogen bond of length of 3.05(1) Å. The structures of dehydro-Phe containing peptides suggest that the dehydro-Phe promotes the β-turn II conformation. The five-membered pyrrolidine ring of the Pro residue adopts an ideal Cγ-exo conformation with torsion angles χ11 = -24(1)°, χ12 = 34(1)°, χ13 = -30(1)°, χ14 = 15(1)°, and θ10 = 6(1)°. The side chain torsion angles in dehydro-Phe are χ21 = -1(2)°, χ22, 1 = -176(1)°, and χ22, 2 = 8(2)°. The Plane of C2α-C2β-C2γ is rotated with respect to the plane of the phenyl ring at 7(1)°, which indicates that the atoms of the side chain of dehydro-Phe are essentially coplanar. The molecules form a 21 screw axis related hydrogen-bonded rows along the b axis.
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  • 95
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    Biopolymers 29 (1990), S. 543-547 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A fast Monte Carlo integration algorithm with varying time step is described for cooperative binding of ligands of arbitrary length to a one-dimensional lattice. This algorithm is particularly suitable for strongly cooperative or anticooperative systems, i.e., when the time scales for different kinetic events are very different. As an application, the kinetics of a bimodal two-ligand system are briefly discussed.
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  • 96
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    Biopolymers 29 (1990), S. 549-557 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The preparation of copolypeptides consisting of L-aspartic acid and L-glutamic acid was performed to determine the effects of copolymer composition and sequential distributions on the rate of degradation by papain in a PECF (pseudoextracellular fluid) at pH 4.75 and 7.40, at 37.0°C, to simulate in vivo polymer degradation. Random copolymers consisting of β-benzyl L-aspartate and γ-benzyl L-glutamate were synthesized by the N-carboxyanhydride method. Water-soluble copolymers were obtained by successive reactions of side chains by anhydrous HBr treatment. All the samples were found to be degraded by random chain scission with papain. Further, the degradation data for the samples followed the Michaelis-Menten rate law, being the first order in papain concentration. The nature of side chains are important to the rate of degradation by papain and it was controlled by the comonomer composition as well as the sequential distribution of comonomers in the copolymer chains.
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  • 97
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    Biopolymers 29 (1990), S. 491-500 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: By combining electrophoresis with movements of fluorescence pattern after photobleaching (MOFPAP), which is abbreviated as EMOFPAP, we are able to measure electrophoretic mobilities of large DNA fragments in an agarose gel within a fairly short time scale (about 10 min or even down to 1 min). The new method represents a significant improvement in experiment time when compared with the time (typically on the order of hours) required to determine the average electrophoretic mobility of large DNA fragments in agarose gels by means of either conventional gel electrophoresis or pulsed-field gel electrophoresis. In this article, we present the EMOFPAP experimental setup and consider optical conditions, including beam profile geometry and fluorescence pattern formation. A realistic formula that can explain the parameters governing the EMOFPAP method using our present optical setup has been derived. A comparison of results between experimental and computer simulation data is made, and an optimization of the EMOFPAP method is proposed.
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  • 98
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    Biopolymers 29 (1990), S. 559-565 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The elastic modulus (G′) of factor XIIIa induced fibrinogen gels was found to be substantially lower than the G′ of fibrin gels that were formed by clotting fibrinogen with thrombin. The addition of fibronectin and/or the reducing reagent dithiothreitol (DTT) to the factor XIIIa coagulation mixture led to the formation of a weaker gel structure, while the rigidity of thrombin induced clots was not appreciably affected by the inclusion of the DTT but increased somewhat in the presence of fibronectin. The reasons for the differing clot rigidities are discussed in terms of biochemical mechanisms.
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  • 99
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    Biopolymers 29 (1990), S. 567-596 
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvent effects on the thermodynamics of two processes - folding of proteins and association between proteins - are examined in detail. A complete inventory of the multitude of solvent effects may be obtained by employing the concept of conditional solvation free energy. This theoretical tool allows for the isolation of specific side-chain effects from the entire protein and for the study of its contribution to the overall free energy change in small model compounds. Some numerical examples are presented, and ways of estimating other cases, for which no relevant experimental data are available, are suggested. Our findings lead to the conclusion that the currently used hydrophobicity scales, based on partition coefficients between water and an organic solvent, are inadequate measures of the contribution of side chains being transferred from water to the interior of the protein. We have also tentatively concluded that correlation between hydrophilic functional groups might be more important than correlations between hydrophobic side chains.
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  • 100
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of Melanin-concentrating hormone (MCH) fragments have been synthesized and their biological activities compared with the parent peptide. The substructural units, 5-14 linear and 5-14 cyclic, have been used as models for MCH -  in 1H-nmr conformational studies. Conformational features predicted by molecular dynamics analyses find support in the nmr experiments.
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