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  • Polymer and Materials Science  (24)
  • Life Sciences (General)  (14)
  • AERODYNAMICS
  • 1995-1999  (37)
  • 1955-1959  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Design and characterization of thermosetting polyimide structural adhesive and composite matrix systems (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 2943-2954 
    Details
    ISSN: 0887-624X
    Keywords: phenyl ethynyl ether imides ; amorphous or semicrystalline morphology ; volatile free thermosetting matrix ; structural adhesives ; composites ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fully cyclized, organo soluble, phenylethynyl-terminated, ether-imide oligomers of 2-10,000 g/mol (Mn) were prepared by the reaction of 2,2′-bis[4-(3,4-dicarboxyphenoxy)phenyl]-propane dianhydride (bisphenol-A dianhydride, BPADA) with a stoichiometric excess of either para, meta, or isomeric mixtures of phenylene diamine and phenylethynylphthalic anhydride (4-PEPA) endcapper. High para-containing oligomers produced semicrystalline powders, but the all meta isomer was completely amorphous. The lower molecular weight oligomers displayed an attractive low viscosity melt and were cured to very high gel content networks at 350-380°C for 30-90 min. The cured 3000 g/mol oligomers showed a (DSC) glass transition temperature (Tg) of 267°C and produced tough, solvent-resistant films. Excellent adhesion to surface-treated titanium alloys was achieved, as judged by single-lap shear measurements. Resin infusion molding was conducted, which permitted low-void, graphite-fabric composite panels to be prepared. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2943-2954, 1997
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Catalytic chain transfer for molecular weight control in the emulsion homo- and copolymerizations of methyl methacrylate and butyl methacrylate (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 859-878 
    Details
    ISSN: 0887-624X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The behavior of catalytic chain transfer in semi-batch emulsion polymerization has been studied for two monomers, viz, methyl and n-butyl methacrylate. Two different catalytic chain transfer reagents were used with different water solubilities: cobaloxime boron fluoride (COBF), which was found to partition approximately equally between organic and aqueous phases, and tetra-phenyl cobaloxime boron fluoride (COPhBF), which was found to reside predominantly in the organic phase. The difference in hydrophilicity between the two transfer agents was found to affect the polymerization mechanism. COBF exhibited superior transfer behavior in all cases, whereas the restricted mobility of the COPhBF had a deleterious effect on the efficiency of the transfer mechanism. The best results were achieved under monomer flooded conditions using COBF. MALDI-TOF mass spectrometry analysis shows catalytic chain transfer to be the dominant mechanism initiating and stopping chain growth as none of the chains appear to have initiator fragment end groups. Analysis of copolymers by MALDI-TOF mass spectrometry reveals both molecular weight and composition data. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 859-878, 1997
    Additional Material: 21 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of solvent on the homo-propagation rate coefficients of styrene and methyl methacrylate (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 2311-2321 
    Details
    ISSN: 0887-624X
    Keywords: styrene ; methyl methacrylate ; pulsed-laser polymerization ; “living” free radical ; propagation rate coefficient ; solvent effects ; benzyl alcohol ; N-methyl pyrrolidinone ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The free radical propagation rate coefficients of both Methyl Methacrylate (MMA) and Styrene (STY) have been measured using Pulsed-Laser Polymerization. The effect of solvents on the propagation rate coefficient, kp, is reported for several solvents, namely, bromobenzene, chlorobenzene, dimethyl sulphoxide, diethyl malonate, diethyl phthalate, benzonitrile, and benzyl alcohol, at 26.5°C. This preliminary data indicated that benzyl alcohol (BzA) had a large effect on the MMA propagation reaction. As earlier work indicated that N-methyl pyrrolidinone (NMP) would also have a large effect on the kp of MMA, Arrhenius parameters were evaluated for both MMA and STY at two different concentrations of monomer in BzA and NMP. BzA had a significant effect (at 95% confidence) increasing both the activation energy (Ea) and the preexponential factor (A) for MMA and STY. In NMP, a similar trend is observed for MMA polymerization; however, while a solvent effect on STY was observed, the effect on Ea and A was too small to discern with confidence. A series of additional experiments was performed to evaluate the influence of camphorsulfonic acid (CSA) as an additive in STY polymerization. There was no effect of CSA on kp, confirming that the strong effect CSA has on “living” radical polymerization of styrene does not originate from complexation leading to an accelerated propagation step but rather by altering the ratio of active-to-dormant chains in the reaction. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2311-2321, 1997
    Additional Material: 12 Ill.
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  • 4
    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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  • 5
    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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  • 6
    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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  • 7
    Electronic Resource
    Electronic Resource
    Simulation of free radical addition reactions modified by the presence of cobalt macrocycles (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Theory and Simulations 4 (1995), S. 195-208 
    Details
    ISSN: 1022-1344
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Free radical addition reactions in the presence of cobaloximes and related compounds have been modelled. Several mechanisms are presented and similarities with the “persistent radical effect” noted by Daikh and Finke are discussed. Cobaloximes and salophenSystem. name: N-acetyl-p-aminophenyl salicylate. derivatives are widely used in organic synthesis to build carbon-carbon bonds, whereas in polymer synthesis they are used as catalytic chain transfer agents in the production of oligomers. This work shows that these reactions are closely related and also demonstrates the influence that an external radical source has on the overall reaction kinetics.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mats.1995.040040114
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  • 8
    Electronic Resource
    Electronic Resource
    Atom transfer radical copolymerization kinetics (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 19 (1998), S. 371-375 
    Details
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Starting from the basic radical mechanism of atom transfer radical polymerization (ATRP), simple expressions are derived for the description of atom transfer radical copolymerization kinetics. It is shown that kinetic parameters are interchangeable between atom transfer and conventional free-radical copolymerization, which is important for two reasons. Firstly, it enables the prediction of the average equilibrium constant (and hence average rate of polymerization) in an ATRP system with two monomers if the corresponding conventional kinetic parameters are known. Secondly, it enables the determination of the relative fractions of propagating radicals by a detailed ATRP study.
    Additional Material: 1 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Synthesis and properties of poly(1-alkyl-3-methylene-2-pyrrolidone)s (1996)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 197 (1996), S. 3123-3133 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A series of α-methylene-N-alkyl-2-pyrrolidone monomers with varying length of the alkyl chain from C1 to C8 were synthesised. The monomers were subjected to free radical polymerisation to yield a range of polymers each with a different balance in hydrophobic/hydrophilic properties originating from the pyrrolidone moiety and the N-alkyl chain. The equilibrium water content of polymers crosslinked with ethylene dimethacrylate were found to decrease with increasing alkyl chain length. The glass transition temperatures of the polymers are reported ranging from 98°C to -5°C on going from the methyl to the octyl derivative. The thermal degradation of the polymers was studied using thermogravimetric analysis and pyrolysis gas chromatography-mass spectroscopy. The polymers were found to degrade at ca. 400°C predominantly via an unzipping mechanism. Pyrolysis at 450°C results in five products.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1996.021971006
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  • 10
    Electronic Resource
    Electronic Resource
    Mechanism of catalytic chain transfer in the free-radical polymerisation of methyl methacrylate and styrene (1998)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 1697-1708 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The mechanism of catalytic chain transfer with bis(boron difluorodimethylglyoximate) cobaltate(II) (COBF) has been studied in the homopolymerisations of methyl methacrylate and styrene. The chain transfer constants were measured using both the Mayo and Chain Length Distribution (CLD) methods over a range of temperatures (40-70°C). The two methods generally agree within 10%. The high values of the chain transfer rate coefficients, ktr (∼107 for MMA), suggest the possibility that the reaction is approaching diffusion control. This is also supported by the high values obtained for the frequency factor (A ∼ 1010). The chain transfer rate coefficients for styrene are approximately two orders of magnitude lower than those obtained for MMA, which can be explained in terms of the formation of cobalt-carbon bonds and the accessibility of β-H sites for hydrogen abstraction from the two different radical chain ends in the case of styrene. High conversion, solution polymerisation experiments on methyl methacrylate in toluene reveal behaviour inconsistent with a simple catalytic mechanism and may suggest deactivation of the catalyst by solvent. On the assumption that the kinetics of catalytic chain transfer can be explained by a classical free-radical mechanism, it is possible to derive information on the chain length dependence of the average termination rate coefficient, 〈kt〉. Applying this approach to methyl methacrylate and styrene at different temperatures, we have found that the chain length effect on 〈kt〉 appears to be independent of both temperature and monomer type.
    Additional Material: 18 Ill.
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