Studies of the role of acetone triplets in the initiation of vinyl polymerization

Triplet acetone generated from the thermal decomposition of tetramethyl-1,2-dioxethane was shown to be incapable of initiating the free radical polymerization of methyl methacrylate and styrene. Triplet acetone is rapidly quenched by energy transfer to the monomer, but the excited state of the monomer so produced does not initiate polymerization. Acetone does not initiate polymerization when irradiated into its $\text{n}\text{−π}{}^{\mathrm{\ast }}$ singlet state with UV irradiation in the absence of a co-sensitizer, but is effective when photolysed in the presence of triethylamine which quenches the acetone, possibly by resulting in the efficient formation of ketyl radicals. In contrast, methyl tert-butyl ketone is an effective initiator because of the more rapid rate of formation of radicals by α-cleavage when one of the substituents gives rise to a tertiary alkyl radical.