Cationic polymerization of isobutylene catalyzed by iBuAlCl2 in the presence of ethers: Effect of catalyst pre-activation and mixture of two ethers

The cationic polymerization of isobutylene using pre-activated by the wet argon or salts hydrates (BuAlCl2)-Bu-i as catalyst in the presence of diisopropyl ether in n-hexane at 10 degrees C as a starting temperature and high monomer concentration ([IB] = 5.8 M) has been investigated. It was shown that pre-activated (BuAlCl2)-Bu-i possessed high activity (> 90% of monomer conversion in 10 min) and unexpectedly high regioselectivity of beta-H abstraction at rather low ether to Lewis acid ratio ((Pr2O)-Pr-i/(BuAlCl2)-Bu-i = 0.4). The use of pre-activated (BuAlCl2)-Bu-i as a co-initiator leads to formation of more uniform active species that results in narrowing of molecular weight distribution as compared to polyisobutylenes synthesized with non-preactivated (BuAlCl2)-Bu-i. Much better control over polydispersity can be achieved by using of mixture of two ethers of different basicity and steric structure (diethyl and diisopropyl ethers) as additive instead of one (diisopropyl ether) during IB polymerization co-initiated by pre-activated (BuAlCl2)-Bu-i. Under optimized conditions ([(BuAlCl2)-Bu-i (pre-act).] = 38 mM, [Et2O] = [(Pr2O)-Pr-i] = 7.6 mM, [H2O] = 0.033 M, time: 15 min), desired low molecular weight (M-n similar to 1000 g mol(-1)) highly reactive polyisobutylenes in high yield (> 90%) with high content of exo-olefin end groups (> 80%) and relatively low polydispersity (M-w/M-n = 2.4-2.7) were readily synthesized at high reaction temperature (10 degrees C) and monomer concentration ([IB] = 5.8 M). (C) 2016 Elsevier Ltd. All rights reserved.