Controlling polymer topology by atom transfer radical self-condensing vinyl polymerization of p-(2-bromoisobutyloylmethyl)styrene

摘要

A new unsymmetrical AB* inimer, p-(2-bromoisobutyloylmethyl)styrene (BiBMS), was applied to the atom transfer radical polymerization (ATRP) to prepare a family of polymers with the topologies ranging from linear to branched. The catalyst system was Cu/CuBr_2 coupled with 2,2'-bipyridine (Bipy) or N,N-bis(2-pyridylmethyl)octylamine (BPMOA) as a ligand in toluene or anisole at different temperatures, which ensured a very low catalyst (CuBr) concentration throughout the polymerization by a slow reduction process. First, BiBMS was polymerized in anisole at 0 °C using Cu/CuBr _2/BPMOA as a catalyst system; at this temperature, the initiating activity of the formed A* was frozen and the polymerization was a step-growth polymerization, resulting in the formation of a linear polymer (LP1) whose main chain was linked by ester bonds. Second, BiBMS was polymerized in toluene at 20 °C using Cu/CuBr_2/Bipy as a catalyst system. Under this condition, initiation from the B* of BiBMS was slow, followed by a fast radical polymerization of the BiBMS vinyl bonds and a slow deactivation, thereby affording another linear polymer (LP2), the structure of which was the same as that obtained by common free radical polymerization of BiBMS except the end groups. The conversion of BiBMS was controlled to be moderate to suppress the possible initiation from the pendant B* along the polymer main chain. Third, BiBMS was polymerized in anisole at various temperatures using Cu/CuBr_2/Bipy as a catalyst system; three branched polymers (BP1, BP2, BP3) with different degree of branching (DB) were obtained, the DB of which could be easily adjusted by changing temperature (BP1, DB = 0.12 at 20 °C; BP2, DB = 0.26 at 40 °C; BP3, DB = 0.37 at 60 °C).