Polyisobutylene with High exo-Olefin Content via β-H Elimination in the Cationic Polymerization of Isobutylene with H2O/FeCl3/Dialkyl Ether Initiating System

Abstract

The cationic polymerizations of isobutylene (IB) with H2O/FeCl3/dialkyl ether initiating system were conducted in dichloromethane (CH2Cl2) at temperatures from −20 to +20 °C, in which the dialkyl ether includes diethyl ether (Et2O), dibutyl ether (Bu2O) or diisopropyl ether (iPr2O). The highly reactive polyisobutylenes (HRPIBs) with high content of exo-olefin end groups (−CH2−C(CH3)═CH2) 82−91 mol % and acceptable monomodal molecular weight distribution (Mw/Mn = 1.7−2.3) could be successfully synthesized at low concentration of FeCl3 at 0.005 mol·L−1 at 0 or even 10 °C. These results are comparable to those of commercial HRPIBs produced industrially at far below 0 °C. The directly rapid β-proton elimination from −CH3 of the growing chain ends and chain transfer reaction to monomer were dependent on concentration of iPr2O·FeCl3 complex (1:1), concentration of free iPr2O ([free iPr2O] = [iPr2O] − [FeCl3]) if (iPr2O·FeCl3> 1) and polymerization time. The much higher concentration of PIB chains formed in the ...