The photolysis of polymethylvinylketone. I. Reactions and kinetics

The photolysis of polymethylvinylketone has been studied in solution. The two primary reactions which occur upon absorption of a quantum of ultra-violet light by the carbonyl group have been shown to be similar to those which occur with simple aliphatic ketones; namely, the type I split to form a polymer radical and a free methyl or acetyl radical, and the type II split at the C$\chembond{1,0} $C linkage $\alpha $ $\chembond{1,0} $ $\beta $ to the carbonyl which results in a decrease in the molecular weight of the polymer and the formation of a double bond. The kinetics of the molecular weight changes have been followed by viscosity, osmotic pressure and ultracentrifuge measurements on the degraded polymers, and it is shown that these can be explained on the basis of a competing reaction which opposes the breakdown by type II. A mechanism is proposed for this reaction which involves a 'repolymerization' due to the addition of free radicals to the double bonds formed by type II.