Some observaions on the effect of the physical nature of the separating phase on the rate of heterogeneous polymerization

Study of the polymerization of methyl methacrylate and acrylonitrile in aqueous solution in a redox-initiated system consisting in Na<SUB>2</SUB>S<SUB>2</SUB>O<SUB>4</SUB>-K<SUB>2</SUB>S<SUB>2</SUB>O<SUB>8</SUB> reveals the fact that the initial rate of polymerization increases with increase in concentration of the catalyst or activator, and this is followed by a fall in rate with a further increase in concentration of either of the two, and finally the rate is found to increase again with higher concentration of the catalyst or activator. This peculiarity in the kinetics of the above heterogeneous polymerization seems to be connected with the physical state of the separating phase. In the region where the rate is increasing with increasing catalyst concentration, the insoluble phase is in the form of a fine sol. In the region where the rate falls with increased catalyst or activator concentration, the separating phase is in the form of a coarser, less stable sol (milky sol or latex). In the region where the rate again increases, the insoluble phase is in the form of a coarse precipitate or coagulum. The D.P. is observed to run more or less parallel with the rate. The above observations may have bearing on the kinetics of the emulsion polymerization and "explosive" polymerization