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Mechanism of discoloration of irradiated polyvinyl chloride
Author(s) -
Ohnishi ShunIchi,
Nakajima Yoshiharu,
Nitta Isamu
Publication year - 1962
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1962.070062405
Subject(s) - radical , polyene , electron paramagnetic resonance , chemistry , photochemistry , irradiation , molecule , reaction mechanism , polyvinyl chloride , salt (chemistry) , polymer chemistry , chloride , organic chemistry , catalysis , nuclear magnetic resonance , physics , nuclear physics
The radiation chemical process in polyvinyl chloride has been studied by means of electron spin resonance, optical spectroscopy, and measurement of gas evolution. The chief technique was to irradiate samples at −196°C. and then follow the change or changes with rising temperature. Resonance results showed that, on irradiation, several primary radicals, such as CH 2 ĊHCH 2 , CHClĊHCHCl, etc., were produced. Among them some CH 2 ĊHCH 2 radicals could recombine to form crosslinks during irradiation even at −196°C. A mechanism for the discoloration of PVC, based upon results obtained by these three different methods, has been postulated. Discoloration is caused by the formation of polyenyl radicals or polyene molecules of considerable conjugation lengths, some as long as 9 conjugated double bonds. Polyenyl radicals are produced as a result of a thermally induced secondary reaction of the CHClĊHCHCl radical, above −70°C., thereby accompanied by hydrogen chloride detachment following the so‐called “zipper” mechanism. An equation relating the pressure of evolved HCl to the reaction temperature has been derived by a simple kinetic treatment of the zipper reaction. Some effect of heat treatment and increasing dose on discoloration was discussed.