摘要:

AbstractThe polymerization of γ‐benzyl‐DL‐glutamate NCA in the presence of poly(γ‐benzyl‐L‐glutamate) was investigated. At the initial stage theD‐enantiomer was preferentially polymerized (ca. 35% ee) by using triethylamine as an initiator. Enantioselectivity was independent of the molecular weight of preformed poly(γ‐be

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210601

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe primary fragmentation mechanisms in the thermal decomposition of several polycarbonates were studied by direct pyrolysis into the mass spectrometer. Our results indicate that ester exchange reactions predominate in the primary thermal fragmentation process of polycarbonates, causing the formation of cyclic oligomers.

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210602

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe primary fragmentation mechanisms in the thermal decomposition of several polyurethanes were studied by direct pyrolysis into the mass spectrometer. Ester exchange reactions predominate in the primary thermal fragmentation process, causing the formation of cyclic oligomers, which are subsequently cleaved to open‐chain oligomers containing hydroxyl end group

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210603

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractA detailed analysis of the reaction products generated by reorganization of polycarbonates with piperazine, performed by direct mass spectrometry methods, has shown that this reaction actually follows the pathway postulated and that, at 50% piperazine incorporation level, urethanediphenol compounds are almost exclusively produced. This allowed us to obtain, by repolymerization with phosgene, alternating copoly(carbonate‐urethanes) with thermal stabilities comparable to those of the parent polyurethanes. The primary fragmentation mechanisms in the thermal decomposition of these copolymers were studied by direct pyrolysis into the mass spectrometer. Ester exchange reactions predominate here, causing the formation of cyclic oligomers, which are subsequently cleaved to open‐chain oligomers containing hydroxyl end gro

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210604

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractHET acid was condensed with either ethylene glycol or 1,4‐butanediol to yield the respective oligoesters. These oligoesters were characterized by molecular weight, measured by vapor‐pressure osmometry. The degradation mechanism of oligoesters of HET acid with either ethylene glycol or 1,4‐butanediol was elucidated. The thermal properties of these polyesters were studied using differential thermal analysis and thermal volatilization analysis. The mechanism of degradation was proposed on the basis of pyrolysis–gas chromatography studies, the degradation products being subsequently identified by mass spectrometry. It turned out that in the course of decomposition, hexachlorocyclopentadiene was formed, which is believed to be the active substance for flame retardance in these systems. The aspect of tailoring flame retardancy by changing the chemical environment, i.e., by using different diols, is di

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210605

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe size distributions of a number of different polycondensations with nonself‐condensing monomers were calculated by a kinetic method. The results of linear polycondensations with and without reversibility or stoichiometry and of multifunctional polycondensations are exactly the same as those obtained by Flory with probability methods and do not differ, when comparable, from the size distributions produced by the polycondensation of self‐condensing monomers. Size distributions were also obtained for reactions in which the order of reaction changes with conditions or during reaction. These results clearly show that a Flory distribution is obtained as long as the principle of equal reactivity applies at any given instant, although this reactivity may vary in the course of the react

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210606

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThis article reports a continuation of our work on the substituent effects on the preferred helical conformations and the mutarotation of substituted poly(L‐prolines). The size of the substituent has been increased from a methyl group to an ethyl group in the 5 position. The purpose is twofold: (i) according to our theoretical conformational energy calculations, an ethyl group in the 5 position can exert a greater steric effect than can a methyl group; and (ii) the rotation‐isomerization of the ethyl group introduces a new intriguing fact to the problem. Thecisisomer of 5‐ethylproline was synthesized by catalytic hydrogenation of Δ′‐2‐ethylpyrroline‐5‐carboxylic acid, whereas fortrans‐5‐ethylproline, a chemical separation method involvingp‐toluenesulfonyl chloride was used. The resolution ofcis‐5‐ethylproline and the assignment of absolute configurations have been carried out by fractional crystallization and circular dichroism spectroscopic techniques, respectively. Poly(cis‐5‐ethyl‐D‐proline) was obtained from its correspondingN‐carboxyanhydrid

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210607

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractInitiation and propagation processes in thermally initiated solid‐state polymerization of sodium acrylate have been studied. The kinetics of initiation, followed with the electron spin resonance technique, leads to an activation energyEof 28.8 kcal/mol, which is attributed to the formation of dimeric radicals. The activation energy of 16 ± 1 kcal/mol obtained for the solid‐state polymerization of sodium acrylate by chemical analysis and differential scanning calorimetry has been attributed to the propagation pro

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210608

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractThe polymerization of acrylamide (M) in aqueous sulfuric acid medium initiated with ceric ammonium sulfate–malic acid redox pair was investigated at 35 ± 0.2°C under nitrogen atmosphere. The initiation was caused by the free radical generated by the decomposition of the complex formed between ceric ion and malic acid (MA). The rate of monomer disappearance was proportional to the first power of malic acid, ceric ion, and monomer concentrations at lower ceric ion concentrations. However, at higher ceric ion concentrations the rate was independent of [Ce(IV)]. The rate of ceric ion disappearance was proportional to [MA]and [Ce(IV)] but independent of [M]at lower ceric ion concentrations. The activation energy was found to be 57.74 kJ/mol. Sulfuric acid retarded the reaction. Molecular weights increased with increasing [M] and decreasing [Ce(I

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210609

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY

摘要:

AbstractBased on our recent discovery of the isomerization polymerization of β‐(2‐acetoxyethyl)‐β‐propiolactone into poly‐δ‐ester,1,2we examined the generality of this phenomenon by using two related monomers. The catalysts were (EtAlO)nand Et(ZnO)2ZnEt. The side‐chains in the monomers selected were the (CH3)2CHCOOCH2CH2(2) and (CH3)CICHCOOCH2CH2(3) groups in which steric effects are almost identical but electronic effects are in opposition. The monomers yielded isomerized poly‐δ‐ester units, depending on the terminal substituent groups in the side‐chain. These observations can be interpreted with the bicyclic intermediate proposed in the earlier work. Monomer (2) was reactive and produced a poly‐δ‐ester structure most readily, probably because of the higher electron density at the side‐chain ester group which coordinated with the catalyst. In contrast, monomer (3) was less reactive, and the probability of isomerization was the lowest, i.e., the electron deficient side‐chain ester group apparently interfered with the formation of the intermediate, especially in the Zn‐catalysis. Equibinary random copolymers were prepared from (2) and (3) according to the cat

ISSN:0360-6376    

DOI:10.1002/pol.1983.170210610

出版商:John Wiley&Sons, Inc.    

年代:1983

数据来源: WILEY