KINETICS OF 2-PHASE BULK-POLYMERIZATION .2. INFLUENCE OF DISSOLVED POLYMER

In the reported experiments, the effect of dissolved polybutadiene on the initial rate of polymerization of styrene was investigated by using high-precision dilatometric techniques. The dissolved polymer reduced the rate of polymerization by amounts greater than can be accounted for by a reduction in monomer concentration. Rate reductions increased with the amount of dissolved polybutadiene and with its mol. wt and were greater for benzoyl peroxide initiator than for equal concentrations of azobisisobutyronitrile. Good quantitative agreement was obtained with the number-average length of the growing polymer chains, whether varied by using different initiators, changing initiator level, or adding chain-transfer agent. These results are inconsistent with a chemical mechanism, but they are explained by a proposal originated by North and Reed whereby the dissolved polymer makes the reaction mass a ″poorer″ solvent for the growing polymer chains, reducing their overall coil dimensions and enhancing their rate of diffusion together for termination.