Controlled cationic polymerization of styrene using AlCl3OBu2 as a coinitiator: Toward high molecular weight polystyrenes at elevated temperatures

The controlled cationic polymerization of styrene using CumOH/AlCl₃OBu₂/Py initiating system in a mixture CH₂Cl₂/n‐hexane 60/40 v/v at ?40 and ?60 °C is reported. The number‐average molecular weights of the obtained polystyrenes increased with increasing monomer conversion (up to M_n = 85,000 g mol^?1) although experimental values of M_n were higher than the theoretical ones at the beginning of the reaction that was ascribed to slow exchange between reversible‐terminated and propagating species. The molecular weight distribution became narrower through the reaction and leveled of at the value of M_w/M_n = 1.8–2.0. A kinetic investigation revealed that the rate of polymerization was first‐order in AlCl₃OBu₂ concentration meaning that monomeric counteranion (AlCl₃OH^? or AlCl) involved in the initiation and propagation steps of the reaction. It was also found that the rate of polymerization decreased with lowering temperature, which could be attributed to a decrease in concentration of free Lewis acid (AlCl₃), the true coinitiator of polymerization, because of an increase in the tightness of its complex with dibutyl ether. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3736–3743, 2010