Copolymerisation radiochimique du styrene avec l'acrylonitrile en solution

The radiation-initiated copolymerization of styrene and acrylonitrile was investigated at 20° in dimethylformamide (DMF) and in benzylalcohol solutions. The compositions of the copolymers were only slightly affected by these polar solvents. The influence of temperature on the copolymerization in DMF solutions was studied in greater detail. It was found that the acrylonitrile content in the copolymer obtained at -78° drastically increased as a result of an anionic polymerization of acrylonitrile. Fractional precipitation of the products obtained at -78° showed that they were not mixtures of polymers but were block copolymers containing long sequences of acrylonitrile units. This copolymer is assumed to arise as a result of the simultaneous growing of the two ends of a primary radical-ion, acrylonitrile adding to one end by an anionic mechanism while the free radical end initiates a random copolymerization of styrene and acrylonitrile. The anionic contribution to the over-all process was established. The anionic homopolymerization of acrylonitrile was studied in DMF, toluene and their mixtures. The rate was found to exhibit a maximum for 20% acrylonitrile in DMF. It was further noticed that significant amounts of DMF could be replaced by toluene or styrene without affecting the rate. The reduction in rate in more concentrated monomer solutions was attributed to an autoinhibition of acrylonitrile in its anionic polymerization.