Cationic polymerization of styrenes by protonic acids and their derivatives, 1. Rates and molecular weight distributions of polystyrenes formed by some sulfonic superacids

The cationic polymerizations of styrene by sulfonic superacids (CF3SO3H, FSO3H, and ClSO3H) and by methanesulfonic acid (CH3SO3H) were investigated with respect to the polymerization rate and the molecular weight distribution (MWD) of the polymer at 0°C. The superacids initiated the polymerization at low concentrations. CF3SO3H is the most active initiator among the protonic acids investigated so far. The polystyrenes formed in methylene chloride showed a MWD with two distinct peaks irrespective of the kind of initiators. In benzene only the low molecular weight polymer is formed, in nitrobenzene only the high molecular weight polymer. This indicates that in methylene chloride all the initiators generate two kinds of propagating species which grow simultaneously and independently. The time‐course of the polymerizations depended on the kind of initiators, in that CF3SO3H gave first‐order polymerizations to completion, while FSO3H and ClSO3H gave limited yields. The termination mechanism is also discussed.