Formation of conjugated polyenes by chemical and thermal degradation of vinyl chloride copolymers and other vinyl polymers

Abstract Raman and infrared spectroscopic studies on the chemical degradation products of two vinyl chloride/vinyl acetate copolymers and a vinyl chloride/vinyl acetate/vinyl alcohol terpolymer, obtained with the system potassium tert‐butoxide/N,N‐dimethylformamide, show that substantially complete dehydrochlorination occurs. Although the vinyl acetate groups are hydrolysed to the corresponding alcohol these latter largely remain intact and block the extension of the polyene sequences, whose lengths, measured by Raman spectroscopy, are in agreement with values calculated from the initial polymer composition. No degradation other than hydrolysis occurs with vinyl acetate and vinyl alcohol homopolymers or a vinyl alcohol/vinyl acetate copolymer. The thermal degradation of the copolymers containing vinyl chloride, and of two vinyl chloride homopolymers of differing syndiotacticity, at 153°C in N,N‐dimethylformamide, gives both dehydrochlorination and elimination of the comonomer units, the latter reaction occurring at least as rapidly as the former. A crosslinked structure, in which there is some steric stabilisation and, hence, conjugated polyene sequence lengths up to about 40, is formed. A maximum sequence length of 8 is found in thermally degraded poly(vinyl acetate), but the conjugated polyenes are too short to be detected in degraded poly(vinyl alcohol) and the vinyl alcohol/vinyl acetate copolymer.