Degradation of poly(vinyl chloride) by u.v. radiation—II: Mechanism

✍ Scribed by C. Decker

• Publisher: Elsevier Science
• Year: 1984
• Tongue: English
• Weight: 500 KB
• Volume: 20
• Category: Article
• ISSN: 0014-3057
• DOI: 10.1016/0014-3057(84)90201-5

✦ Synopsis

A~traet--The mechanism of the light-induced degradation of solid poly(vinyl chloride) (PVC) has been investigated, and an overall reaction scheme has been developed, based on values of the quantum yields for the primary photoproducts. Only a very small fraction (0.2%) of the excited polyenes induces the degradation of PVC, primarily by photocleavage of the allylic C--C1 bond. The high instability of fl-chloroalkyl radicals is responsible for the chain dehydrochlorination that leads to formation of polyenes. In the absence of 02, chain scissions and crosslinking are postulated to originate mainly from ct-chloroalkyl radicals through fl-cleavage of C--C bonds and radical coupling, respectively. In the presence of 02, the chain dehydrochlorination still proceeds, together with an oxidative chain process which yields, via peroxy and alkoxy radicals, hydroperoxides, ketones and peroxide crosslinks. Cleavage of the polymer backbone results most probably from the decomposition of tertiary alkoxy radicals by a carbon-carbon fl-scission process.