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  • Polymer and Materials Science  (45)
  • Humans  (29)
  • 1995-1999  (38)
  • 1990-1994  (36)
  • 11
    Electronic Resource
    Electronic Resource
    Studies of alkylthio-substituted aromatic diamines as curatives for polyurethane cast elastomers (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 28 (1990), S. 3701-3724 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of alkylthio-substituted aromatic diamines was synthesized using a convenient high yield procedure. The method consisted of heating a mixture of dialkyl disulfide and aromatic diamine in the presence of cuprous iodide or other Lewis acid catalyst. Dialkyl disulfide was continually replenished as consumed, throughout the reaction, to maintain the desired reaction temperature. Compounds so prepared were isolated by first precipitating the catalyst with solid caustic and then vacuum flashing the crude products. When desired, the final product purity could be increased by washing with acid to remove starting material or reaction intermediates. The final products were often liquids or low melting solids and showed utility as curatives for polyurethane cast elastomers. Alkylthio substitution of the aromatic diamines lowered reactivity toward isocyanates and generally provided for facile processing during molding. The series of derivatives allowed for great flexibility in controlling both diamine reactivity and the physical properties of the final elastomers. These benefits arose from the diverse electronic, steric and isomeric properties of the derivatives. Polymers were prepared from the alkylthio-substituted compounds and commercially available TDI-based prepolymers using conventional cast elastomer techniques. The physical properties of the polymers were determined and their relation to alkylthiodiamine structure examined.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1990.080281315
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  • 12
    Electronic Resource
    Electronic Resource
    Preparation and properties of poly(alkyl vinyl ether-2-ethyl-2-oxazoline) diblock copolymers (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 1709-1717 
    Details
    ISSN: 0887-624X
    Keywords: poly(methyl vinyl ether); poly(butyl vinyl ether) ; poly(2-ethyl-2-oxazoline) ; block copolymers ; living cationic polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A method for the synthesis of well-defined poly(alkyl vinyl ether-2-ethyl-2-oxazoline) diblock copolymers with hydrolytically stable block linkages has been developed. Monofunctional poly(alkyl vinyl ether) oligomers with nearly Poisson molecular weight distributions were prepared via a living cationic polymerization method using chloroethyl vinyl ether together with HI/ZnI2 as the initiating system and lithium borohydride as the termination reagent. Using the resultant chloroethyl ether functional oligomers in combination with sodium iodide as macroinitiators, 2-ethyl-2-oxazoline was polymerized in chlorobenzene/NMP to afford diblock copolymers. A series of poly(methyl vinyl ether-2-ethyl-2-oxazoline) diblock materials were found to have polydispersities of ≈ 1.3-1.4 and are microphase separated as indicated by two Tg's in their DSC thermograms. These copolymers are presently being used as model materials to study fundamental parameters important for steric stabilization of dispersions in polar media. © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1993.080310709
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  • 13
    Electronic Resource
    Electronic Resource
    Determining the chromophore in the amylopectin-iodine complex by theoretical and experimental studies (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 32 (1994), S. 2257-2265 
    Details
    ISSN: 0887-624X
    Keywords: helix in amylopectin-iodine complex ; I4 unit in amylopectin-iodine complex ; spectra of amylopectin-iodine complex ; amylopectin-iodine chromophore composition ; amylopectin fine structures and complex formation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A partial hydrolysis of amylose followed by the addition of iodine provides a spectrum almost identical to that of the amylopectin-iodine (API) complex suggesting the involvement of smaller “amylose-like” units in the API complex. Our theoretical studies on different polyiodine and polyiodide species suggest that a nearly linear I4 unit stabilized within the cavity of a small “amylose-like” helix is responsible for the characteristic API spectrum. Since there are 2.75 anhydroglucose residues (AGU) for every iodine atom in the amylose-iodine (AI) complex and a structural similarity exists between the API and the AI (amylose-iodine) complexes, we identify (C6H10O5)11I4 to be the chromophore in the API complex. © 1994 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1994.080321207
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  • 14
    Electronic Resource
    Electronic Resource
    Z-RNA: The solution NMR structure of r(CGCGCG) (1990)
    New York : Wiley-Blackwell
    Biopolymers 29 (1990), S. 109-122 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Left-handed double-helical Z-RNA has been studied using the ribohexanucleotide pentaphosphate r(CpGpCpGpCpG). One-dimensional proton nmr experiments were used to probe the structural details of the left-handed helix in concentrated sodium perchlorate solution. In 1M NaClO4 the RNA adopts the normal A-form double helix, and in 6M NaClO4 it is nearly all in the Z form. In 4M NaClO4 it exists as nearly equal parts of A form and Z form. Resonances corresponding to both A and Z form appear in the nmr spectrum, indicating that the duplex exchanges slowly between forms. Spin-spin coupling constants between protons in the ribose rings were used to determine the sugar-pucker conformations of the individual nucleotides. Quantitative nuclear Overhauser experiments were used to determine proton-proton distances within the nucleoside, and from these distances values for the glycosidic torsion angle were determined. The results show that the cytidines adopt C2′,-endo sugar puckers (S type) with pseudo-rotation phase values (P) of ∼ 165°. The bases are in the anti conformation, with χ values of ∼ - 140°. The internal guanosines adopt C3′,-endo sugar puckers (N type) with P ∼ 18°, while the 3′-terminal guanosine ribose exists in an equilibrium between S- and N-type conformations. All three guanosine bases adopt the syn conformation, with χ ∼ 70°. The results indicate that the solution structure of Z-RNA is very similar to that of Z-DNA.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360290116
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  • 15
    Electronic Resource
    Electronic Resource
    Morphiceptin and β-casomorphin-5 analogues containing a reduced peptide bond: Selective μ-receptor agonists and a novel μ antagonist, H-Tyr-Proψ(CH2-NH)Phe-Pro-Gly-OH (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 957-969 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to prevent enzymatic degradation of β-casomorphin-5 (1) and morphiceptin, reduced peptide bonds were incorporated at the 2-3 and 3-4 bonds, respectively. The analogues were synthesized by a combination of solid phase methodology and reductive alkylation of resin-bound peptide amines with Boc-amino acid aldehydes (Boc: tert-butyloxycarbonyl) in the presence of NaBH3CN. During reversed phase high pressure liquid chromatography purification, peak shape distortions could be observed. Epimerization was excluded, based on gas chromatography/mass spectroscopy analysis, which indicated acceptable levels of racemization (〈3%) in the crude product. Instead, the phenomena could be attributed to slow cis/ trans isomerizations originating from the Xxx-Pro bonds in the sequence. The presence of different conformational isomers was also established by 1H-nmr spectroscopy in DMSO-d6. All analogues showed high stability in blood plasma, enhanced binding affinity for the μ receptor, and very low binding to the δ receptor. While the Phe3Ψ(CH2-N) Pro4 analogues (3) and (5) displayed agonist activity, the Pro2Ψ(CH2-NH) Phe3 modified analogue (2) showed antagonist activity comparable to D-Phe-Cys-Tyr-D -Trp-Arg-Thr-Pen-Thr-NH2.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360320807
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  • 16
    Electronic Resource
    Electronic Resource
    Effect of crosslinking on the properties of poly(2-hydroxyethyl methacrylate) hydrogels (1991)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 189 (1991), S. 195-205 
    Details
    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: 2-Hydroxyethyl-methacrylat wurde durch Initiierung mit γ-Strahlung in Masse mit zwei verschiedenen tetrafunktionellen Monomeren (Ethylenglycol-dimethacrylat und 1,2-Bis(acryloxymethyl)-tetramethyldisiloxan) und einem hexafunktionellen Monomeren (1,1,1-Trimethylolpropan-trimethacrylat) als Vernetzungsmittel copolymerisiert. Die erhaltenen Xerogele wurden anschließend mit Wasser bis zum Erreichen der Gleichgewichtsquellung behandelt. Um die drei Vernetzungsmittel vergleichen zu können, wurde unter Berücksichtigung von Molmasse und Funktionalität der Xerogele die theoretische Konzentration an Vernetzungsstellen zwischen 0,032 und 0,644 mol/l variiert. Die relative Hydrophobie der drei Vernetzungsmittel hat einen ausschlaggebenden Einfluß sowohl auf die Gleichgewichtsquellung als auch auf den Elastizitätsmodul der gequollenen Gele. Der Gehalt an nicht-einfrierbarem Wasser in mit 1,1,1-Trimethylol-propan-trimethacrylat vernetzten Gelen wurde anhand von DSC-Untersuchungen analysiert. Das Verhältnis von nicht-einfrierbarem zum Gesamtgehalt an Wasser in den Gelen nimmt mit steigender Vernetzungsdichte zu.
    Notes: By means of γ-irradiation 2-hydroxyethyl methacrylate has been copolymerized in bulk with two different tetrafunctional monomers, ethylene glycol dimethacrylate and 1,3-bis(acryloxymethyl) tetramethyl disiloxane and with a hexafunctional monomer, 1,1,1-trimethylolpropane trimethacrylate. The resultant xerogels were subsequently swollen to equilibrium in water. In order to allow a comparison among the three crosslinkers, their molar masses and funtionalities were taken into account, the theoretical crosslink concentrations being varied from 0.032 to 0.644 mol dm-3. The relative hydrophobicity of the three crosslinkers was found to have a significant effect on both the equilibrium swelling and elastic modulus of the swollen gels. Non-freezing water in several gels crosslinked with 1,1,1-trimethylolpropane trimethacrylate was analysed by differential scanning calorimetry (DSC). The proportion of non-freezing water in the gel relative to the overall water content was found to increase with increasing crosslink density.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1991.051890118
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  • 17
    Electronic Resource
    Electronic Resource
    Conformational restriction of Tyr and Phe side chains in opioid peptides: Information about preferred and bioactive side-chain topology (1996)
    New York : Wiley-Blackwell
    Biopolymers 38 (1996), S. 1-12 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The side chain of Tyr and Phe was fixed into the gauche (-) or gauche (+) conformation by using the Tic or Htc structures, and into the trans conformation by using an aminobenzazepine-type (Aba) structure. When incorporated into dermorphin or deltorphin II, the Tic and Htc analogues all showed a large decrease in both μ and δ affinities and activities. Fixation of Phe3 in the trans rotamer resulted in a large increase in δ affinity in the dermorphin analogue, whereas in the [Aba3-Gly4] deltorphin II analogue, good δ affinity is maintained despite the removal of the Glu side chain. Whereas several authors propose a gauche (-) preferred conformation for the Phe3 side chain, these results suggest a trans conformation at the δ receptor. The use of these conformationally constrained residues for evaluating the preferred solution conformation in the flexible N-terminal tripeptide Tyr-D-Ala-Phe is illustrated. The 1H-nmr parameters - chemical shift, temperature dependence, and nuclear Overhauser effects to the D-Ala2 methyl protons in the different analogues - provide direct evidence to confirm the proposed sandwich conformation in the native peptides. © 1996 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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  • 18
    Electronic Resource
    Electronic Resource
    A facile synthesis of polyamides from aromatic diisocyanates and dicarboxylic acid catalyzed by Lewis acids (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 17 (1996), S. 897-903 
    Details
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Aromatic polyamides were prepared by an AlCl3 or HCl-catalyzed polymerization of toluene diisocyanate or methylenebis(phenyl isocyanate) with adipic acid at low temperatures (≤100°C) in a short reaction time (3-4 h). The intrinsic viscosity of the polymers was approximately 1.1 dL/g as determined at 25°C with m-cresol as solvent, indicating that the polyamides obtained by this method have relatively high molecular weights. The polymers exhibit high glass transition temperatures and good thermal stability.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1996.030171208
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  • 19
    Electronic Resource
    Electronic Resource
    Solvent effects in copolymerization (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 16 (1995), S. 207-210 
    Details
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Extension of the Mayo-Lewis Model of copolymerization concerning solvent effects in free-radical polymerization is discussed on the basis of the bootstrap and penultimate unit effects.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/marc.1995.030160309
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  • 20
    Electronic Resource
    Electronic Resource
    Ab initio molecular orbital calculations on the transition state for the addition of a methyl radical to vinyl monomers (1994)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 3 (1994), S. 905-913 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Ab initio molecular orbital calculations have been performed on the transition state for the addition of methyl radical to twelve vinyl monomers using the SV 3-21G basis set. A linear relationship has been found between the calculated energies of activation and previously calculated energies of reaction. This supports the assumption of an Evans-Polanyi type rule in previous work which attempted to correlate reactivity with calculated energies of reaction. The activation energies obtained for methyl addition to butadiene and styrene were calculated to be negative. This is caused by errors introduced by a number of sources, viz. basis set superposition error, spin contamination and zero point energy. These errors are discussed. Previous authors have reported reasonable agreement between calculated activation energies at SV3-21G and experimental values for methyl addition to ethylene, this work suggests that this agreement was coincidental and results from the fortuitous cancellation of errors. The nature of the transition state for these radical addition reactions is discussed and the limitations of the SV3-21G basis set are highlighted. The theoretical prediction of activation energies for radical addition reactions would require much larger calculations, beyond the computational means of most research laboratories.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1994.040030507
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