Pseudocationic Polymerization. The End of a Controversy? 1

The behavior of the polymerization of styrene induced by perchloric acid is examined, emphasizing its kinetics and the molecular weight distribution (MWD) of the resulting polymers. The chain transfer to monomer explains the behavior of this reaction near ambient temperature. The results of low-temperature experiments provide a deep insight into the nature of the propagating species, proving their ionic structure, whereas they are incompatible with the postulated propagation by the esters assumed to be the active species by the proponents of the pseudocationic hypothesis. The results of stopped-flow experiments, the effects of the added salts, and the MWD of the produced polymers all point to the ionic character of this polymerization and to the important role of ion pairs.