Reactions of methyl radicals with poly(vinylacetophenone) during photolysis

The photochemistry of isotopically labelled poly(vinylacetophenone) (PVAP) has been investigated, with a view to determining the point of H-atom abstraction from the polymer. Poly(α-d-vinylacetophenone) (DPVAP) and poly β-β dideuterovinyl(acetophenone) (D₂PVAP) were irradiated under high vacuum with long wave u.v. radiation (⩾ 300 nm). From the nature of the gaseous products, it was confirmed that both underwent initial photo-decomposition by a Norrish Type I reaction. Rates of abstraction reactions by CH₃ and CH₃CO radicals from DPVAP were subject to an isotope effect of 8.3; the corresponding rates for D₂PVAP were about 85% of those observed for PVAP. In addition, no significant yields of deuterated products were obtained from D₂PVAP. It is concluded that abstractions occur preferentially at the α-C-atom, in line with predictions based on the energetics of abstraction reactions. Molecular weight increases (due to cross-linking which involves interactions of macro-radicals generated by abstraction reactions) confirm the involvement of the α-C-atom.