Quantitative Synthesis of exo-Olefin-Terminated Polyisobutylene: Ether Quenching and Evaluation of Various Quenching Methods

Abstract

Addition of excess dialkyl ether, e.g., diisopropyl ether (DIPE) or di-sec-butyl ether (DSBE), to a TiCl4-co-initiated, living carbocationic polymerization of isobutylene (IB) results in capping of the chain ends with oxonium cations, as evidenced by cessation of polymerization. Structure of PIB diisopropyl oxonium cations was determined using 500 MHz 1H NMR, by introducing DIPE to a mixture of TiCl4 and 2-chloro-2,4,4-trimethylpentane (TMPCl), a model for the PIB chain end, at −70 °C in CS2/CD2Cl2 (50/50, v/v). One-pot, two-step quantitative synthesis of mono- and telechelic (difunctional) exo-olefin-terminated polyisobutylene (PIB) was achieved by quenching living PIB with DIPE, followed by termination with methanol at −60 °C. TMPCl and 1,3-bis(1-chloro-1-methylethyl)-5-tert-butylbenzene (bDCC) were used as mono- and difunctional initiators, respectively. 1H NMR spectroscopy was used to characterize end-group composition of PIBs. Percent formation of exo olefin was directly related to the steric bulk of...