摘要:

AbstractThree topics are discussed. First, structural irregularities are considered in connection with polyformaldehyde,. poly(vinyl chloride) and poly(vinyl acetate) and with the stabilities of polymers in general. The second topic concerns the distribution of sites of reaction when polymers are modified chemically. The final section deals briefly with polymeric reagents, including some designed for photochemical systems.

ISSN:0258-0322    

DOI:10.1002/masy.19880200105

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe hydrolytic method using 72% sulphuric acid was modified in order to characterize the graft copolymer cellulose‐g‐poly(vinyl acetate‐co‐methyl acrylate). This method involves appropriate cellulose hydrolysis conditions, and the extraction of a fraction of cellulose only when the samples have a low ratio of synthetic polymer to cellulose. In this way, an undesired chemical transformation of the grafted chains is avoided and the polysaccharide is completely removed from the synthetic polymer. This method might be extended to other cellulosic graft copolymers whose carbohydrate part cannot be completely separated and their grafted chains are labile in the reaction conditions reported in the lit

ISSN:0258-0322    

DOI:10.1002/masy.19880200106

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractMultiblock copolymers of styrene and propylene oxide were synthesized by coupling together poly(propylene glycol) and telechelic dihydroxy‐polystyrene with 2, 4‐toluene diisocyanate(TDI) as the coupling agent. The results showed that it was better to terminate the telechelic dihydroxy polystyrene with TDI first, then react with poly(propylene glycol). The copolymer obtained in this two‐step method contains less homopolymers than that obtained when all the three reagents reacted together in one step. The crude product can be purified by extractions with absolute ethyl alcohol and decalin in order to remove the unreacted poly(propylene glycol) and polystyrene, respectively. The purified products were characterized by IR, TH NMR, GPC, membrane osmometry, elemental analysis and shown to be multiblock copolymers of styrene and propylene oxide. The multiblock copolymer exhibits two transition temperatures(Tg's) and behaves like a thermoplastic elastomer at 20–30% polystyrene content. Addition or 2% of the copolymers to the blends of polystyrene and epichlorohydrin rubber improves evidently their mechanical properties and causes the two Tg's to become

ISSN:0258-0322    

DOI:10.1002/masy.19880200107

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe effect of monomer concentration on the graft polymerization of 4‐vinylpyridine (4‐VP) and of 2‐vinylpyridine (2‐VP) on cellulose and on partially carboxymethylated cellulose (PCMC) initiated by cerium ammonium nitrate (CAN) in dilute nitric acid has been examinated. The grafting parameters: grafting efficiency (GE), graft yield (G), graft frequency (GF), and ceric ion consumption ((Ceiv)c)were studied as a function of the monomer concentration. The fraction of poly(4‐vinylpyridine), P(4‐VP), in the graft polymer increased with increasing monomer concentration for both cellulosic substrates. The molecular weight of the grafted P(4‐VP) was obtained viscosimetrically after hydrolyzing away the cellulose backbone. When 2‐VP was grafted on PCMC and on unmodified cotton, the graft yields also increased with monomer concentration, but they were much smaller than in the previous case. Presence of carboxymethyl groups in cellulose enhanced G,

ISSN:0258-0322    

DOI:10.1002/masy.19880200108

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe kinetics of the thermal cyclodehydration reaction of poly‐(1, 3‐phenyl‐1, 4‐phenyl)‐hydrazidea)to poly‐(1, 3‐phenyl‐1, 4‐phenyl)‐oxadiazoleb)have been studied by thermo‐gravimetrical analyses. Both an isothermal method and the non‐isothermal Ozawa method have been used to evaluate the kinetic parameters. The kinetics seem to depend upon the physical state of the polymer i.e. the rubbery or glassy state. During isothermal conversions at elevated temperatures the polymer is expected to be initially in its rubbery state followed by a rubber‐glass transition showing a considerable transition in the observed kinetics. The results obtained from the non‐isothermal Ozawa method and the isothermal method agreed well for the polymer in its glassy state. With the non‐isothermal method the process can be followed as a function of the degree of conversion. In this way a parallel reaction could be observed which starts at the end of the conversion process. The morphological state or the history of the polymer seems to have a considerable influence on the kinetics. The film form of the polymer shows a much higher convers

ISSN:0258-0322    

DOI:10.1002/masy.19880200109

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractTwo series of nucleophilic substitution reactions on PVC using either the same nucleophile but different experimental conditions or various nucleophiles in cyclohexanone (CH) dilute solutions, were performed. The evolution of unreacted iso‐, hetero‐and syndiotactic triads with degree of conversion was followed by 13 C NMR. While the kinetics and yield changed markedly with both the type of nucleophile and the reaction conditions the stereochemical structure of modified polymers proved to depend only on degree of substitution. These results afford further support to a conformational mechanism of substitution, as proposed by earlier wo

ISSN:0258-0322    

DOI:10.1002/masy.19880200110

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractStudies of initiation by azobis(isobutyronitrile) and benzoyl peroxide are discussed. Consideration is given to initiators containing carbon‐13 or carbon‐14 for end‐group analyses, and also to the applications of radical‐trapping techniques for study of oxygen‐centred radicals. Other topics dealt with are (a) head‐addition of primary radicals to monomers, (b) the formation of end‐groups by primary radical termination and by transfer to initiator, and (c) the involvement of stilbene‐like compound

ISSN:0258-0322    

DOI:10.1002/masy.19880200111

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe initiation of the polymerization of styrene by AIBN has been studied at 59, 8°C and 69, 9°C, using Galvinoxyl as a free radical scavenger, by spectrophotometric means. Rates of 7×10−9and 2×10−8mol·1−1· s−1have been measured for the scavengeable free radicals formation in the initiation process of the thermal polymerization of pure styrene, respectively. Values of 6×10−6s−1and 2, 4×10−5s−1have been obtained for the rate constants of production of scavengeable pairs of free radicals (kdf) from AIBN assuming

ISSN:0258-0322    

DOI:10.1002/masy.19880200112

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe radical polymerization of N‐vinylimidazole (VIm) along an atactic poly(methacrylic acid) (PMAA) template in aqueous solution at 50°C was investigated by varying [PMAA]0from 0 to 0.7 basemol/dm3at constant [VIm]0of 0.41 mol/dm3. Rate enhancements were observed only beyond [PMAA]0of 0.18 basemol/dm3. By studying the initial pH and ηsp/c of the polymerization mixtures and taking account of preferential adsorption of protonated VIm on PMAA, part of which is probably mobile, a mechanism is sugges

ISSN:0258-0322    

DOI:10.1002/masy.19880200113

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe polymerization of methyl methacrylate (MMA) initiated by ceric ammonium nitrate ‐ disaccharide redox systems has been studied in aqueous nitric acid at 30°C. The rate of polymerization and the rate of ceric ion disappearance were measured. The dependence of the rates on disaccharide and Ce(IV) concentrations have been evaluated. The reaction involves the formation of a complex between the metal ion and the reductants, whose decomposition gives rise to the initiating free radicals. The termination step takes place predominantly by mutual interaction between growing polymeric radica

ISSN:0258-0322    

DOI:10.1002/masy.19880200114

出版商:Hüthig&Wepf Verlag    

年代:1988

数据来源: WILEY