Cationic polymerization of p-methoxystyrene co-initiated by B(C6F5)3: Effect of acetonitrile and proton traps

Abstract

The cationic polymerization of p-metoxystyrene co-initiated by B(C6F5)3 in CH2Cl2/CH3CN mixtures at room temperature has been studied. It was shown that in the presence of acetonitrile the polymerization proceeds in a quasiliving fashion affording poly(p-methoxystyrene)s with high molecular weight (Mn > 30,000 g mol−1) and low polydispersity (Mw/Mn < 1.35). The increase of the fraction of acetonitrile in the reaction mixture leads to the retardation of polymerization and to some increase of molecular weight. However, the addition of proton traps (2,6-di-tert-butylpyridine or pyridine) to the system results in strong reduction of the reaction rate and the appearance of an induction period when the concentration of proton trap is higher than the concentration of adventitious H2O (~5 mM). Moreover, proton traps act as chain-transfer agents under investigated conditions and their addition to the system converts quasiliving polymerization to conventional chain-transfer dominated process. It was demonstrated that initiation of the polymerization proceeds by protons generated via interaction of B(C6F5)3 with adventitious H2O even in the presence of proton traps, while the haloboration mechanism is ruled out. Acetonitrile plays critical role in the mediating of quasiliving polymerization via stabilization of growing species thus affording the obtaining high molecular weight polymers at elevated temperatures.