Chemical reactivity and conformational properties of growing chains. Part 1.—Study on bimolecular radical termination in styrene + methyl methacrylate copolymerization

Abstract

The bimolecular termination reaction in free-radical copolymerizations of alkene-type monomers has been studied on the basis of a model which includes both chain end flexibility and chemical reactivity.

Two parameters, δ_AB and δ_BA, related to the mobility and reactivity of a copolymer segment, have been calculated as functions of the polymerization temperature for the copolymerization of styrene and methyl methacrylate in bulk initiated by azobisisobutyronitrile. Their activation energies have been compared to those of the corresponding δ_A and δ_B values of pure monomers.

A simple correlation between chemical reactivity and segmental flexibility is consistent with our results. At least for the system under study the bimolecular radical termination reaction seems to be kinetically controlled by the chemical reactivity of the chain ends and, more predominantly, by the segmental flexibility of the last portion of the chain.