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, δAB and δBA, 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 δA and δB 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.
