Carbocationic polymerization of isoprene initiated by dimethylallyl derivatives associated with B(C6F5)3

Abstract

The cationic polymerization of isoprene using dimethylallyl derivatives (3,3-DMAX)–B(C₆F₅)₃ as initiating systems has been investigated in detail. In most cases, oligomers of low molar mass (M_n ≤ 1500 g mol⁻¹) and narrow molar mass distribution (M_w/M_n ≤ 2) were formed, which contain isoprene units almost exclusively in a trans-1,4-configuration in combination with saturated ones, with sometimes a higher polymer fraction of high dispersity. Most of the oligomers are terminated by an olefinic terminal group due to intensive transfer via proton elimination whereas a small proportion of X-functionalized oligomers results from chain end recombination with the counterion. Besides, the high molar mass fraction is formed firstly via protonation of oligomer double bonds followed by propagation at low conversion and then via intermolecular branching yielding polyisoprenes with a high branching degree and/or gel formation at high monomer conversion. Most of the elementary reactions involved in these processes were shown to be dependent on the counteranion X of 3,3-DMAX.