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

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Abstract The cationic polymerization of isobutylene using pre-activated by the wet argon or salts hydrates iBuAlCl2 as catalyst in the presence of diisopropyl ether in n-hexane at 10 °C as a starting temperature and high monomer concentration ([IB] = 5.8 M) has been investigated. It was shown that pre-activated iBuAlCl2 possessed high activity (>90% of monomer conversion in 10 min) and unexpectedly high regioselectivity of β-H abstraction at rather low ether to Lewis acid ratio (iPr2O/iBuAlCl2 = 0.4). The use of pre-activated iBuAlCl2 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-pre-activated iBuAlCl2. 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 iBuAlCl2. Under optimized conditions ([iBuAlCl2 pre-act.] = 38 mM, [Et2O] = [iPr2O] = 7.6 mM, [H2O] = 0.033 M, time: 15 min), desired low molecular weight (Mn ∼ 1000 g mol−1) highly reactive polyisobutylenes in high yield (>90%) with high content of exo-olefin end groups (>80%) and relatively low polydispersity (Mw/Mn = 2.4–2.7) were readily synthesized at high reaction temperature (10 °C) and monomer concentration ([IB] = 5.8 M).