ALBERT

Notes: Unter Annahme einer unelastischen Streuung von quasi-freien Festkörperladungsträgern an adsorbierten Gasmolekeln bei heterogen katalysierten Reaktionen wird ein einfaches Modell entwickelt, welches erlaubt, den Anstieg der katalytischen Aktivierungsenergie bei zunehmender Abweichung der Energie der Stoßpartner vom Resonanzpunkt der Energieübertragung mathematisch zu beschreiben. An einfachen Zerfallsreaktionen wird die Gültigkeit dieses Modells sowie der daraus entwickelten Gleichung gezeigt.

Notes: Depending on the coagulation conditions, poly(p-phenylene-1,3,4-oxadiazole) in the solid state forms two modifications, as can be evidenced by FTIR spectroscopy and by wide-angle X-ray scattering curves (WAXS). In both cases each modification is detectable by characteristic peaks. Processing of fibers or films from solutions in concentrated sulfuric acid by coagulation in water results in the formation of a thermodynamically non-equilibrium form, defined as β-modification. Under special conditions it is possible to obtain the three-dimensionally ordered equilibrium α-structure that leads to processing products with markedly higher tenacities.

Notes: Es wurden Untersuchungen zur chemischen Kopplung heterogener Polystyrol-Polybutadien-Blends bei Einsatz eines organischen Sulfonylazids während des Schmelzemischens im Laborinnenmischer angestellt. Die Wirksamkeit des Kopplungsagens wurde anhand infrarotspektroskopischer, mikroskopischer und dynamisch-mechanischer Analysen sowie anhand des merchanischen Eigenschaftsbildes der Belends beurteilt. Die sich in der Schmelze bildenden Pfropfcopolymeren führen zu einer Erhöhung der Phasenwechselwirkungen un dami zu einer Verbesserung der Festigkeits- und Zähigkeits-eigenschaften der Blends.

Notes: A series of new polyhydrazides containing pendent phenoxy groups has been synthesized by low-temperature solution polycondensation of equimolar amounts of diacid dichlorides and 2-phenoxyterephthalic dihydrazide in N-methyl-2-pyrrolidi-none (NMP). The thermal cyclization of the polyhydrazides gave the corresponding poly(1,3,4-oxadiazole)s containing pendent phenoxy groups. The polymers were characterized by viscometry, solubility measurements, IR spectroscopy, differential scanning calorimetry (DSC) and thermogravimetric analysis.

Notes: Electron-donating substituents of N-(arylamine) phthalimides and succinimides promote antioxidative efficiency of these compounds in thermooxidation of polypropylene (190°C, oxygen), while electron-withdrawing substituents contribute to a reduced volatilization of the polymer. 2,6-Ditert.butyl-4-methylphenol (ionol) raises the antioxidative efficiency of 4-methoxy and 4-methyl substituted derivatives displaying a distinct synergism.

Notes: Es wird über die Herstellung und Charakterisierung von dünnen Filmen aus Poly(p-phenylen-1, 3,4-oxadiazolen) berichtet. Die aus H2SO4-Lösungen präparierten Filme besitzen eine gute optische Transparenz und sind mechanisch stabil. Filme aus Michungen mit Polyamiden zeigen ein ähnliches Verhalten und sind aufgrund ihrer thermischen Eigenschaften für spezielle Anwendungen interessant. Bei faserverstärkten Filmen zeigen erste Untersuchungen, daß spezielle Grenzflächenbereiche entstehen.

Notes: Zur Beurteilung des viskoelastischen Verhaltens von Synthesefasern sind zeitaufwendige Relaxationsuntersuchungen erforderlich. Um zu schnelleren Aussagen zu gelangen, werden mathematische Modelle benötigt. Charakteristisch für Synthesefasern ist, daß bereits bei sehr kleinen Dehnungen 〈 1% kein lineares viskoelastisches Verhalten angenommen werden kann. Es wird ein auf der Grundlage der Boltzmann-Theorie erweitertes Modell vorgestellt, welches das nichtlineare viskoelastische Verhalten von Synthesefasern beschreibt. Unter Anwendung des hier vorgestellten Modells wird das Relaxationsverhalten der Synthesefasern Nomex® und PEEK beschrieben und ein Konzept zur Messung und Auswertung des Ergebnisses vorgestellt.

Notes: Two series of aromatic polyamides incorporating silicon together with phenylquinoxaline or with hexafluoroisopropylidene groups have been synthesized and their properties have been characterized and compared with those of related polymers. These polymers are easily soluble in polar amidic solvents such as N-methyl-2-pyrrolidinone and dimethylformamide, and in tetrahydrofuran, and can be cast into thin, transparent films from solution. The polyamides have weight- and number-average molecular weights in the range of 10 000-40 000 and 3 000-6 000, respectively, and polydispersities in the range of 3-10. They show glass transition temperatures in the range of 236°C-275°C and decomposition temperatures above 400°C. The polymer films have low dielectric constants in the range of 3.26-3.68, and good mechanical properties (tensile strength 74-100 MPa, tensile modulus 180-386 MPa), thus being comparable with other high performance dielectrics.

Notes: The conformation of double-helical amylose is influenced by its water environment [A. Imberty, H. Chanzy, S. Perez, A. Buléon, and V. Tran (1988) Journal of Molecular Biology, Vol. 201, pp. 365-378; A. Imberty and S. Perez (1988) Biopolymers, Vol. 27, 1205-1221]. For several low-energy conformations of left-handed amylose double helices, we performed Monte Carlo simulations of the (N, V, T)-ensemble of configurations of water molecules surrounding a single duplex. The crucial point of this simulation is the use of cylindrical periodical boundary conditions with a relatively small asymmetric unit comprising a limited number of water molecules. The output data consists of local maxima of water density in the space near the macromolecule and information on one- and two-membered water bridges between polar groups of amylose as well as energetic characteristics of the system under study.A left-handed antiparallel-stranded conformation of the amylose double helix (rise and twist per glucose unit are 0.343 nm and -58.1°) corresponds to the global minimum of intraduplex potential energy W. Schulz and H. Sklenar (1993) Biopolymers, submitted; W. Schulz, H. Sklenar, W. Hinrichs, and W. Saenger (1993) Biopolymers, to be published. We found that this conformation is favored also by its hydration shell characteristics in comparison to parallel-stranded structures. Three hydration sites per glucose unit in the vicinity of HO6, O6, and O3 could be identified. Regular water bridges forming a network around the duplex were observed. A moderate change of the helical parameters within the family of left-handed antiparallel structures (to a rise and twist per glucose unit of 0.233 nm and -45°) does not have noteworthy consequences for the characteristics of the hydration shell. The location of the hydration sites with respect to the polar groups of amylose and the observed water bridges are in excellent agreement with the hydration geometry of the heavily hydrated antiparallel-stranded left-handed double helix of p-nitrophenyl α-maltohexose described in a high-resolution crystal study [W. Hinrichs, G. Büttner, M. Steifar, Ch. Betzel, V. Zabel, B. Pfannermüller, and W. Saenger (1987) Science, Vol. 238, pp. 205-208; W. Hinrichs and W. Saenger (1990) Journal of the American Chemical Society, Vol. 112, pp. 2789-2796].In the case of parallel-stranded (nonsymmetric or symmetric) double helices, only one hydration site near the (H) O3 group could be identified. No systematic water bridges with sufficient high probability were observed. The sum of the average potential energies of the amylose-water and water-water interactions is not favourable in comparison with the energy for antiparallel-stranded double helices. The water-water interaction is high, i.e., parallel-stranded amylose breaks the structure of liquid water. This effect would explain the insolubility of natural amylose in cold water and support the occurrence of parallel-stranded double helices in crystallites of starch granules and in amylose microcrystals having only low water content [see Imberty et al. (1988) and Imberty and Perez ( 1988) above]. Symmetric parallel-stranded double helices have very well-exposed polar groups and their conformation should be favored in crystals by the ability to form extensively interduplex hydrogen bonds directly or via single water molecules. Single water molecules incorporated into the crystal would compensate for the shortage of donors of hydrogen bonds on the surface of the symmetric parallel-stranded double helix. Indeed, in accordance with diffraction data see Imberty and Perez (1988) above; also A. Imberty, H. Chanzy, S. Perez, A. BulBon, V. Tran (1987) Macromolecules, Vol. 20, pp. 2636-26381 a critical amount of water increases the crystallinity of amylose and only symmetric parallel-stranded double helices would fit into a crystallographic unit cell with c = 1.05 nm. The unfavorable hydration of parallel-stranded double-helical amylose would increase the stability of natural starch granules (e.g., in seeds) and, therefore, be biologically sensible. © 1992 John Wiley & Sons, Inc.

Notes: Monoamino- und Diamino-monocarbonsäuren setzen sich mti D-Glucuronsäure und D-Galakturonsäure über die bisher nicht faßbaren N-Uronoside unter anschließender Umlagerungsreaktion zu den entsprechenden 1-N-Aminosäure-1-desoxy-D-fructuron- bzw. D-tagaturonsäuren (D-Fructuron- bzw. D-Tagaturon-Aminosäuren1) um.