The co-polymerization of styrene and butyl acrylate in benzene solution

An investigation has been made of the co-polymerization of styrene and butyl acrylate in benzene solution with the object of determining the effect of environment on the several steps of a typical co-polymerization reaction. The reaction at 60° was thermally initiated by ¹⁴ C-labelled αα'-azobis iso butyronitrile. The rate of polymerization was obtained from the weight of polymer isolated and the rate of initiation by radioactive assay of initiator and polymer. Microanalysis of the pure co-polymers for carbon allowed calculation of the monomer reactivity ratios which were found to be constant over a wide range of benzene concentration. For each monomer the quantity δ = k _t ^1/α / k _D , calculated by the rate equation for mutual termination, was found to increase with increase of the benzene concentration. The appropriate values of δ were used, along with other relevant quantities, to calculate the ϕ factor, which measures the tendency for termination of chains by interaction of unlike rather than like radicals. This factor is independent of the benzene concentration but is markedly dependent on the monomer feed. In the light of these results the effect of environment and structure of radicals on the rate of their interaction is discussed.