Ionic Polymerization. IX. The Effect of Water in the Cationic Polymerization of Styrene Catalyzed by Stannic Chloride1

This work was undertaken in order to obtain information on the mechanistic role of water on the polymerization of styrene catalyzed by stannic chloride. The polymerization and molecular weight were studied as a function of the concentration of water and of the other reagents in a nitrobenzene-carbon tetrachloride solvent medium at 25°. Unusually stringent drying conditions and a quantitative measure of water permitted the water content in these experiments to be known with high accuracy and allowed data to be obtained not available from previous work. A high vacuum technique was employed for introduction of all reagents, and the polymerization rate was following dilatometrically The initial rate of the reaction was observed to increase to a maximum and then decrease as the initial concentration of water was increased. The decrease in rate has been attributed partly to heterogeneity. At a constant initial water concentration, the reaction was found to be first order with respect to the stannic chloride concentration between 0.005 and 0.02 M, and approximately second order with respect to the monomer concentration between 1 and 3 M. The degree of polymerization of the resulting polymer increases with the initial monomer concentration, decreases with the water concentration, and is essentially independent of the catalyst concentration. A reaction mechanism has been proposed to account for these results, in which a monohydrate catalyst-cocatalyst complex is assumed. Termination is postulated to occur by a spontaneous unimolecular process and a bimolecular process involving water. A monomer transfer step is also indicated.