Initiation mechanisms in radical polymerizations : Reaction of cumyloxy radicals with methyl methacrylate and styrene

Abstract

Cumyloxy (1-methyl-1-phenylethoxy) radicals have been generated by thermolysis (60º) of dicumyl hyponitrite in methyl methacrylate and styrene. The carbon-centred radicals formed by interaction of cumyloxyl with the respective monomers were trapped as stable adducts of 1,1,3,3-tetramethyl-isoindolin-2-yloxyl. Extensive hydrogen atom abstraction and methyl radical generation as well as double-bond addition were observed in methyl methacrylate. Styrene underwent only double-bond addition by both cumyloxy and methyl radicals. Some possible implications of these results for polymer structure are discussed. A kinetic study of the decomposition of dicumyl hyponitrite in cyclohexane at various temperatures gave

k=7.7 × 10¹⁴exp(-13600/T) s^-1

for the rate constant. Rate constants for the addition of cumyloxyl to methyl methacrylate (k ≈ 2 × 10⁴ dm³ mol^-1 s^-1) and styrene (k≈2 × 10⁵ dm³ mol^-1 s^-1) at 60ºhave been estimated.