Abstract
Dilute solutions of poly(α-methylvinylacetophenone) (PMVAP) were exposed to long-wave (( λ ⩾ 300 nm) u.v. radiation under high vacuum conditions. The low molecular weight products, analysed by mass spectrometry, were ethane, methane and CO, and their appearance indicates that PMVAP decomposes via Norrish type I (α cleavage) reactions. The relatively higher ethane yield reflects the greater difficulty of H abstraction by methyl radicals, substitution at the α-C atom forcing the methyls to abstract at the less reactive secondary C atoms. Random chain scission also occurs, and has been attributed to the β scission of macroradicals, which are formed by abstraction reactions involving methyl radicals, and more importantly, carbonyl triplets (photoreduction). Spectroscopic evidence supports the proposed chain scission mechanism.
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