3 years ago

Cationic Copolymerization and Multicomponent Polymerization of Isobutylene with C4 Olefins

Cationic Copolymerization and Multicomponent Polymerization of Isobutylene with C4 Olefins
Jack Emert, Rudolf Faust, Priyadarsi De, Tota Rajasekhar, Ujjal Haldar
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)·bis(2-chloroethyl) ether (CEE) complex in conjunction with tert-butyl chloride (t-BuCl) as initiator in hexanes at 0 °C has been investigated. The reactivity ratio of IB rIB = 1100 was determined for copolymerization of IB and B1 at low conversions, using product compositions obtained from inverse gated 13C NMR analysis. The reactivity ratio of B1 rB1 = 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.; Macromolecules 2015, 48, 5474]. Close to linear first-order plots of ln{[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 (PIB) sec-alkyloxonium ion after B1 incorporation was confirmed by 1H NMR spectroscopy and GC-MS analysis by adding EADC·CEE to a mixture of B1 and 2-chloro-2,4,4-trimethylpentane (TMPCl), a model for the PIB chain end, at 0 °C in cyclohexane-d12. 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 °C. These results are important to understand the mechanism of commercially important highly reactive polyisobutylene (HRPIB) synthesis using mixed C4 olefin feeds.

Publisher URL: http://dx.doi.org/10.1021/acs.macromol.7b01941

DOI: 10.1021/acs.macromol.7b01941

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