Base accelerated degradation of polyvinyl chloride

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Abstract
The degradation at 150°C. of polyvinyl chloride in the presence of base is studied by means of ultraviolet, visible, and infrared spectra. The reaction of polyvinyl chloridebase systems at 150°C. is viewed as a base accelerated dehydrochlorination of polyvinyl chloride proceeding through initiation, propagation, and termination phases. Polyene units with sixteen double bonds in conjugation are considered to be the most probable component of polyene structures contributing to the longest wave length absorption maxima recorded at 550 mμu. Dichroism to polarized light is observed in a plasticized, oriented, base degraded polyvinyl chloride film. This dichroism is considered a confirmation of the assigned polyene structure. The infrared spectra obtained reveal the development, as the reaction progresses, of conjugated carbon‐carbon double bonds, conjugated carbonyl groups, bonded hydroxyl groups such as from hydroperoxides and/or alcohols, and the eventual formation of carboxyl groups. The mechanism of the oxidative degradation at 150°C. is attributed to the attack, after dehydrohalogenation, by molecular oxygen at the olefinic double bonds to form peroxide radicals which by radical chain transfer yield hydroperoxides that degrade to carbonyl containing products.

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