摘要:

The hindered monomer, 2,3,4-trimethyl-3-pentyl methacrylate (I), was synthesized for penultimate effect studies. Since it readily homopoiymerized (km111≠ 0) and readily copolymerized with styrene, copolymerizations of I with styrene were carried out at 60°C in benzene with AIBN as initiator. The conversion to copolymer and the copolymer composition were determined by using GLC techniques. Composition-conversion data was analyzed by performing a computerized nonlinear least-squares fitting to the integrated form of the penultimate model equation. The experimental design included the use of optimized M1°/M2° ratios. The penultimate reactivity ratios calculated from these data were r1′ = 0.23, r1′= 0.59, r2= 0.59, r2′ = 1.34. Thus, when I is the penultimate unit, a terminal styryl radical prefers to add styrene, whereas when styrene is the penultimate unit, terminal styryl radicals prefer to add I. These results constitute the best evidence for a steric penultimate effect yet available in the literature from composition-conversion studies. However, the case is not yet proved. Further studies to strengthen this conclusion are proposed.

ISSN:0022-233X    

DOI:10.1080/00222337908066593

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

For binary copolymers from an acrylic monomer (acceptor type, M1) and an aromatic-substituted monomer (donor type, M2) a linear relation between log (r2/r1) and the probability of “coisotactic” alternating addition is observed. This can be a proof for the influence of monomer polarity on the copolymer configuration.

ISSN:0022-233X    

DOI:10.1080/00222337908066594

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

Alternating copolymers of vinyl acetate (VAc) and maleic anhydride (MA) are produced preferentially when VAc and MA are copolymerized at moderate temperatures while random copolymers are produced at temperatures above 90°C. A charge-transfer complex (CTC) of VAc/MA exists at moderate temperatures but does not exist at temperatures above 90°C.

ISSN:0022-233X    

DOI:10.1080/00222337908066595

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The ortho effect and the additivity of substituent parameters in the reaction between phenols and poly(vinyl acetate) radicals have been investigated in the light of theories postulated by Swain and Lupton on substituent constants Fkand Rkand that of Williams and Norrington on the unique positional weighting factors fjand rj. The present correlation studies show that while Charton's theory that the ortho-substituent effect is primarily electrical is true for most of the substituents, some steric considerations have to be invoked while dealing with groups like o-tert-butyl. The additivity of fjFkand rjRkis much less satisfactory than that of Hammett's [sgrave] or Brown-Okamoto's electrophilic [sgrave]+substituent constants.

ISSN:0022-233X    

DOI:10.1080/00222337908066596

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The propagation step of the polymerization process of tetrahydrofuran was studied in detail. The influence of temperature and dielectric constant of the reaction medium on the rate and equilibrium constants of the elementary steps of the reaction was investigated. As the changes of temperature result in changes of the dielectric constant of the medium, it was found necessary to give the dependence of the reaction constants on both these parameters simultaneously.

ISSN:0022-233X    

DOI:10.1080/00222337908066597

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

9-Ethynylanthracene has been polymerized at 80°C by use of complex phosphinic, arsinic, and stibinic initiators, e. g., NiCl2′2PPh3, and the obtained products have been divided into benzene-soluble and benzene-insoluble fractions. It has been shown that the benzene-insoluble polymer has a conjugated polyenic structure while the soluble polymer, withMless than 1500 daltons, contains dihydroanthracene units in the backbone in addition to the conjugated double bonds. It has been found that by using the above initiators the polymers are mainly cis. The cis to trans isomerization has been shown by DTA and DSC measurements to occur between 260 and 290° C.

ISSN:0022-233X    

DOI:10.1080/00222337908066598

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

This paper is concerned with analysis of the basic regularities of the kinetics of formation of polymers with a conjugated system. The experimentally found regularities are explained in terms of the proposed chain branched polymerization mechanism. The principal role in the chain polymerization mechanism is played by paramagnetic centers which are formed from the diamagnetic macromolecules of the polymer in the process of synthesis. The formation of paramagnetic centers is also due to the chain mechanism. It has been established that the thermal effect of the reaction leads to localized overheating of the emerging heterophase of the polymer, which has important consequences for the kinetics of polymerization and the rate of formation of paramagnetic centers.

ISSN:0022-233X    

DOI:10.1080/00222337908066599

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

Xanthomonas campestrispolysaccharide in the solid state is stable to 225°C in air and 250°C in inert atmosphere. In solution, even at moderate temperatures, the polymer undergoes hydrolytic degradation via the glycosidic linkages, and occurrence of main-chain scission results in lower solution viscosity. In solution, the polymer can exist in ordered and disordered conformations. In distilled water at temperatures ≤ 50°C, the polymer exists in the disordered conformation. In the presence of salt, acid, or base the polymer exists in the ordered conformation. In the ordered conformation the polymer exhibits a far greater hydrolytic stability. The higher stability of the ordered conformation is especially demonstrated when the polymer is aged in acid or base solutions. Contrary to the expected lower stability of the glycosidic linkages in acid or base than in water,Xanthomonas campestrispolysaccharide shows higher stability in these media.

ISSN:0022-233X    

DOI:10.1080/00222337908066600

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

Vinyl polymerization of acrylonitrile initiated by the Mn3+/ascorbic acid redox system was investigated in aqueous sulfuric acid in the temperature range of 30–45°C. The rate of polymerization Rpand the rate of Mn3+ion disappearance were measured. The effect of additives like water -miscible organic solvents, neutral salts, complexing agents and different surfactants on the initial rate of polymerization were investigated. Depending on the results obtained, a suitable reaction mechanism is suggested which involves the formation of a complex between Mn3+ion and the acid whose decomposition generates the initiating free radical, with the polymer chain being terminated by mutual combination of the growing chains.

ISSN:0022-233X    

DOI:10.1080/00222337908066601

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor

摘要:

The present investigation describes the kinetics and the mechanism of the inhibiting action of chalcone on the rate of Ce(IV)-initiated polymerization of acrylonitrile in the temperature range 30–40°C. The effect of monomer, metal ion, chalcone, perchloric acid, acetic acid, sodium sulfate, and manganese sulfate on the rate of polymerization has been studied. The most striking observation in the present investigation was the rate mechanism. The plot of [M]/Rpversus 1/[M] gave a negative intercept which appears to be a general phenomenon for all inhibiting substrates. The activation parameters were calculated, and a suitable reaction scheme is proposed.

ISSN:0022-233X    

DOI:10.1080/00222337908066602

出版商:Taylor & Francis Group    

年代:1979

数据来源: Taylor