Liquid coordination complexes as a new class of catalysts for the synthesis of highly reactive polyisobutylene

Abstract

A number of acidic liquid coordination complexes (LCCs) based on phosphorus-containing electron donors such as tri-n-octylphosphine oxide (POct3O), triphenylphosphine oxide (PPh3O) or triphenylphoshine (PPh3), and Lewis acids (AlCl3, FeCl3, TiCl4) have been synthesized and tested as catalysts of cationic polymerization of isobutylene. Among different LCCs studied, POct3O–AlCl3 and POct3O–FeCl3 (χ(MCl3) = 0.60) in combination with bis(2-chloroethyl)ether (CE) and iPr2O, respectively, showed best results in terms of monomer conversion, exo-olefin end group content and polydispersity. POct3O–AlCl3/CE catalytic system afforded highly reactive polyisobutylene (HR PIB) with high exo-olefin end group content (75–90%) and low polydispersity (Đ≤2.0) in high yield (70–90%) at 20 °C and high monomer concentration ([IB] = 5.2 M) in n-hexane, although the number-average molecular weight (Mn = 2.500–3.500 g mol−1) is slightly higher than required for application. POct3O–FeCl3/iPr2O catalytic system showed higher activity and regioselectivity in the cationic polymerization of isobutylene as compared to POct3O–AlCl3/CE giving desired low molecular weight HR PIB (Mn = 1500 g mol−1, Đ = 2.1, Fn(exo) = 91%) in quantitative yield at lower catalyst concentration (22 mM for POct3O–FeCl3 vs. 44 mM for POct3O–AlCl3) at room temperature.