COMPUTER-SIMULATION OF THE AGGREGATION OF ION-PAIRS IN THE POLYMERIZATION OF STYRENE INITIATED BY RCL SNCL4/NR(4)(+)CL(-) SYSTEMS/

Computer simulations show that ion pair aggregation can be responsible for the unusual dependence of the initial rate of polymerization on t he concentration of added salt in the cationic polymerization of styre ne initiated by RCl/SnCl4/NBu(4)(+),Cl-. Addition of small amounts of tetraalkylammonium chloride to the system reduces the rate of polymeri zation due to the decrease of the concentration of propagating free ca tions. Subsequent salt addition leads to a small rate increase, and th en the rate decreases at higher [salt](0)/[SnCl4](0) ratio. The simula tions show that the rate increase can be ascribed to the formation of aggregates of ion pairs and thus to a higher overall proportion of car bocations resulting in faster polymerization. The decrease of the poly merization rate at higher concentrations of added salt can be explaine d by the conversion of free SnCl4 to SnCl5- anions which are weaker Le wis acids. The effect of various equilibrium constants on the total co ncentration of carbocations as a function of added salt is simulated.