Cationic Copolymerization and Multicomponent Polymerization of Isobutylene with C4 Olefins

摘要

Cationic polymerization of isobutylene (IB) in the presence of other C4 olefins, 1-butene (B1), cis-2-butene (C2B), and 1,3-butadiene (BD) using the ethylaluminum dichloride (EADC)center dot bis(2-chloroethyl) ether (CEE) complex in conjunction with tert-butyl chloride (t-BuCl) as initiator in hexanes at 0 degrees C has been investigated. The reactivity ratio of IB r(IB) = 1100 was determined for copolymerization of IB and B1 at low conversions, using product compositions obtained from inverse gated C-13 NMR analysis. The reactivity ratio of B1 r(B1) = 1 was deduced from theoretical considerations. At low B1 incorporation levels, exo-olefin contents remained high in the copolymers, and the molecular weights were virtually unchanged relative to the experiments with IB alone [Banerjee, S.; et al. Macromolecules 2015, 48, 5474]. Close to linear first order plots of In{[M](0)/[M]} versus time were obtained ([M](0) and [M] are IB concentrations at time t = 0 and t, respectively) when the copolymerization was carried out with [IB] > 2 M. This is because propagation rate increases with increasing [IB] while termination (ion collapse/sec-alkyloxonium ion formation) is independent of [IB]. The formation of polyisobutylene (Pm) sec-alkyloxonium ion after B1 incorporation was confirmed by H-1 NMR spectroscopy and GC-MS analysis by adding EADC center dot CEE to a mixture of B1 and 2-chloro-2,4,4-trimethylpentane (TMPCl), a model for the PIB chain end, at 0 degrees C in cyclohexane-d(12). Olefin formation and ion collapse to TMP-B1-Cl from TMP+-capped B1 were observed by quenching the sec-alkyloxonium ion with methanol at 0 degrees C. These results are important to understand the mechanism of commercially important highly reactive polyisobutylene (HRPIB) synthesis using mixed C4 olefin feeds.