摘要:

An ESR study has been made on the course of grafting of tetrafluoroethylene onto polyethylene. Alkyl and allyl radicals trapped in the polymers were measured under various grafting conditions. It was observed that alkyl radicals decay very rapidly when monomers are in contact with the irradiated polymer, while allyl radicals decay very slowly even in the presence of monomers as in the decay of radicals in irradiated polymers without monomers. The effect of pre-irradiation temperature on grafting was also studied, and the rate of grafting was found to be much faster for lower pre-irradiation temperatures. From these experimental results it was concluded that alkyl radicals play an important Tole in the initiation reaction of grafting.

ISSN:0022-233X    

DOI:10.1080/00222337108061064

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

Radiation-induced grafting of monochlorotrifluoroethylene onto polyethylene was carried out by a pre-irradiation method. It was observed that the grafting proceeds rapidly at temperatures from -35 to 0°C in the liquid monomer phase. By measuring ESR spectra, it was found that the grafting can be initiated by allyl radicals trapped in polyethylene. An absorption band characteristic to the grafting site was found and the band was tentatively assigned to the stretching vibration of the C-F bond situated in the vicinity of the branching position (the initiating site).

ISSN:0022-233X    

DOI:10.1080/00222337108061065

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

An NMR investigation was carried out on random and alternating copolymers of acrylonitrile (AN) with a-methylstyrene (MS) and methacrylonitrile (MAN) with α-methylstyrene and styrene (S). The alternating MS-AN copolymer, prepared by complexation with AlEti1-5Cl1-5, was found to have a predominantly coisotactic configuration which was attributed to the interaction between the CH3and CN groups. The cotacticity of the alternating copolymer was found to be independent of the temperature of polymerization and the amount of AlEt1-5Cl1-5used for complexation. The NMR spectra of random MS-AN copolymers of varying compositions indicated a high value (0.85) for the coisotacticity probability parameter (σ). The equimolar random MS-AN copolymer was also found to have essentially alternating sequences which was attributed to their low reactivity ratios. The equimolar alternating MS-MAN copolymer was found to have a random stereochemical configuration in which the coisotactic placement was slightly preferrred over the cosyndiotactic placement. The NMR spectrum of the equimolar free radical initiated MS-MAN copolymer lacked the fine structure observed in the spectrum of the alternating copolymer which was attributed to the presence of other sequences. The equimolar alternating S-MAN copolymer was found to have a high coisotactic configuration similar to that observed in the MS-AN copolymer. The equimolar free radical initiated S-MAN copolymer had a random sequence distribution.

ISSN:0022-233X    

DOI:10.1080/00222337108061066

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The NMR spectra of random and equimolar alternating copolymers of styrene with a-chloroacrylonitrile were studied. The monomer sequence distribution in the random copolymers, prepared in the presence of free radical catalysts, as determined from NMR analyses, was in accordance with the values expected from the r1and r2values derived from the conventional copolymerization theory. The alternating structure of the copolymer prepared by complexation with AlEt1-5Cl1-5was confirmed. The equimolar random copolymer, prepared by free radical initiation, was shown to contain essentially alternating sequences.

ISSN:0022-233X    

DOI:10.1080/00222337108061067

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The copolymerization of isoprene, butadiene, and other conjugated dienes with maleic anhydride was readily initiated in polar solvents by conventional free radical catalysts, including peroxides, hydroperoxides, and azobisisobutyronitrile, at high concentrations or at temperatures at which the catalyst had a half-life of 1 hr or less and the total reaction time was 0.5-1 hr. Decreasing the reaction temperature or the rate of catalyst addition resulted in increased yields of Diels-Alder adduct and decreased yields of copolymer. The molecular weight decreased as the temperature increased. Dioxane and tetrahydrofuran peroxides, obtained by the passage of oxygen or UV irradiation in air, also initiated the copolymerization. The soluble diene-maleic anhydride copolymers were equimolar and alternating, had [n] 0.1-6 (cyclohexanone) and contained 75-95% 1,4 structure according to ozonolysis, titration with IC1 and NMR. The IR spectrum of the butadiene–maleic anhydride copolymer indicated 75-95% cis-1,4, 5-20% trans-1,4 and 0-5% 1,2-vinyl unsaturation. The proposed mechanism of polymerization involves a donor-acceptor (diene-dienophile) interaction generating a ground-state charge transfer complex which is readily converted to the cyclic adduct. Under the influence of radicals the ground-state complex is transformed into an excited complex which undergoes polymerization. High concentrations of radicals are necessary to generate polymerizable excited complexes in competition with adduct formation.

ISSN:0022-233X    

DOI:10.1080/00222337108061068

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

A study is presented on the kinetics of living polymerization in which the propagation rate constants decrease to zero at a certain degree of polymerization of the propagating chain. The general solution for the distribution function and the rate of polymerization is given and two special cases are discussed. When all the propagation rate constants are the same up to a critical degree of polymerization and null beyond it, the polymerization proceeds approximately as a normal living polymerization until the number-average degree of polymerization reach 85 to 90% of the critical value. When the propagation rate constants decrease linearly with the degree of polymerization, the distribution of living polymer is narrower than the usual Poisson distribution and the reaction order of the rate of polymerization with respect to monomer concentration is between first and second and is affected by the initial monomer and catalyst concentrations.

ISSN:0022-233X    

DOI:10.1080/00222337108061069

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

An ambiguity in use of the term functionality is pointed out. The two most widely used relations (Flory, and Stockmayer and Kahn) connecting extent of reaction at the gel point and functionality are examined. The relations are shown mathematically to lead to the same result when all assumptions and definitions are considered. Measured gel points of polyesters are compared with those predicted by the equation. Deviations were less than 10% of the predicted values.

ISSN:0022-233X    

DOI:10.1080/00222337108061070

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

The values of the CH3/CH2ratios measured from accumulated NMR spectra of polyethylenes samples are in good agreement with those obtained from conventional IR techniques. Because NMR does not require calibration, systematic errors could be less important. Owing to the estimated values of the CH/CH3ratios, tetrasubstituted carbon atoms are present in all the high-pressure polyethylene specimens.

ISSN:0022-233X    

DOI:10.1080/00222337108061071

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

When protein in various liquids containing aromatic hydrocarbons, such as benzene, naphthalene, and phenanthrene, is irradiated by γ-rays from a60Co source the changes in the internal relationships of the atoms in the protein molecule vary with the irradiation liquids containing aromatic hydrocarbons. An empirical equation for the optical rotation was obtained, and the phenomena were explained on the basis of the molecular mechanism. Protein irradiated by γ-rays from a60Co source in air showed the effect of pH on the changes in the internal relationships of the atoms in the protein molecule. An empirical equation for the optical rotation was obtained, and the phenomena were explained on the basis of the molecular mechanism.

ISSN:0022-233X    

DOI:10.1080/00222337108061072

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor

摘要:

When protein was irradiated by γ-rays from a60Co source, a post-irradiation effect of protein reaction was caused. An empirical equation for the optical rotation was obtained, and the phenomena were explained on the basis of the molecular mechanism. The general equation for the optical rotation is given by [α] f= a − b log t, where [α] f is the final specific rotation of the solution, t is time after γ irradiation, and a and b are adjustable constants.

ISSN:0022-233X    

DOI:10.1080/00222337108061073

出版商:Taylor & Francis Group    

年代:1971

数据来源: Taylor