Direct Living Cationic Polymerization of p-Hydroxystyrene with Boron Trifluoride Etherate in the Presence of Water

Abstract

Direct living cationic polymerization of p-hydroxystyrene (pHS) has been developed in the presence of a fairly large amount of water using BF3OEt2 as a Lewis acid catalyst and the adducts (1−4) of p-methoxystyrene (pMOS) and a series of protonic compounds as initiators. In contrast to most living cationic polymerizations, the water and the alcohol adducts (3 and 4, respectively) produced polymers with number-average molecular weights (Mn) close to the calculated values from the monomer/initiator mole ratios. With 4/BF3OEt2, the Mn increased with monomer conversion, and the living nature of the chains was confirmed by sequential monomer addition experiments. The polymerization proceeded even in the presence of a large amount water to afford polymers whose Mn increased in direct proportion to monomer conversion with fairly narrow MWDs (Mw/Mn < 1.4). This initiating system was also effective at or above ambient temperature (from −15 to +60 °C). The success of this controlled cationic polymerization of unprotected pHS is due to the stability of BF3OEt2 and to its tolerance of the hydroxy groups in the monomer and water and the proper selection of the initiator. This initiator contains a covalent C−O bond that is preferentially dissociated by an oxophilic Lewis acid, BF3. This is the first example of a direct living polymerization of pHS, by any mechanism, without protecting the hydroxy groups.