摘要:

This paper brings together the results of our recent studies on various aspects of UV initiated solid-state polymerizations of acrylic and methacrylic acids. The use of polarized UV radiation to initiate the polymerization of acrylic acid at 4°C is consistent with the initial formation of mobile excitons which are subsequently trapped at the imperfections where radicals are eventually formed. Differences in the electron spin resonance spectra and radical concentrations obtained by irradiating samples of methacrylic acid under various conditions in the temperature range − 5O°C to − 20°C demonstrate the existence of a range of imperfections in the crystalline monomer, the nature of which is sensitive to the presence of trace impurities. The molecular mobility in the imperfections is seen to increase with increasing temperature in a manner consistent with broad-line n.m.r. studies on the monomer. These results give information on the mechanisms of initiation and termination. The effect of small applied stresses on the polymerizations is sensitive to both temperature and trace impurities; i.e., factors which affect molecular mobility in the bulkmaterial and in imperfections. Themechanism of the polymerization of crystalline acrylic and methacrylic acids is discussed in terms of these results.

ISSN:0369-1152    

DOI:10.1080/15421406908082749

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

It is well known that “positron e+” interacts with matter and forms a positronium (e+- e−) with the electrons of matter. Both the probability of the positronium formation and the lifetime of positronium are profoundly affected not only by the physical state of molecular substances, such as amount of defects, crystallinity, the size and other properties of crystals, but also by the presence of ions, radicals and excited species, produced in the system. Therefore, one can follow solid state reactions by the measurement of lifetime of positronium and the probability of the formation in the reaction system without any degradative analysis. By applying this method to the radiation-induced reaction in organic crystalline state, polymerization of several monomers such as acrylonitrile, methacrylonitrile, acetoaldehyde and N-vinyl-carbazole, in the crystalline state has been studied in our laboratory. In this paper, the radiation-induced solid state polymerizations N-vinyl-carbazole are reported.

ISSN:0369-1152    

DOI:10.1080/15421406908082750

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

The radiation-induced polymerizations in three different types of monomers under high pressure have been investigated.

ISSN:0369-1152    

DOI:10.1080/15421406908082751

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

A high degree of conversion can be obtained for the solid phase polymerization ofp-vinylbenzamide when initiated thermally or by a post-irradiation technique. The Arrhenius activation energy for the radiation-induced polmerization is 20.3 kcal/mole while the value for the thermally initiated polymerization is 25.8 kcal/mole. EPR data of the polycrystalline sample shows a broad line spectrum which changes shape as the sample is heated from -196° (the irradiation temperature) to 105° (the polymerization temperature). The latter spectrum, is consistent with a radical of the type:

ISSN:0369-1152    

DOI:10.1080/15421406908082752

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

Crystalline hexamethylenediammonium adipate (m.p. 197 °C), the one to one salt of hexamethylenediamine and adipic acid, polymerizes at temperatures below its melting point yielding the corresponding polyamide (Nylon 66). Although there is considerable disorientation of the resulting crystalline polymer, two preferred directions of chain growth have been established both tilted at least four degrees from the unique b-axis of the monoclinic monomer. It has been found that contact with hydrochloric acid vapor catalyzes the polymerization of the monomer, resulting in appreciable polymerization at temperatures as low as 70°C and increased orientation of the polymer. Oriented reflections, attributable to the dimer and tetramer, are observed at all times in the acid catalyzed polymerization but not in the thermally polymerized material, indicating that continuous initiation is taking place in the former reaction.

ISSN:0369-1152    

DOI:10.1080/15421406908082753

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

摘要:

Experimental work was concentrated on attempts to prepare copolymers from solid binary eutectics. Styrene and β-propiolactone were investigated as an example of a system comprising a vinyl and a cyclic monomer. Only a mixture of homopolymers was obtained as a result of γ-irradiation and, more generally, it is maintained that convincing evidence of copolymerization in such systems has not been presented in the scientific literature.

ISSN:0369-1152    

DOI:10.1080/15421406908082754

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor

ISSN:0369-1152    

DOI:10.1080/15421406908082728

出版商:Taylor & Francis Group    

年代:1969

数据来源: Taylor