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

The cationic polymerizations of isobutylene (IB) with H 2 O/FeCl 3 /dialkyl ether initiating system were conducted in dichloromethane (CH 2 Cl 2 ) at temperatures from −20 to +20 °C, in which the dialkyl ether includes diethyl ether (Et 2 O), dibutyl ether (Bu 2 O) or diisopropyl ether (iPr 2 O). The highly reactive polyisobutylenes (HRPIBs) with high content of exo -olefin end groups (−CH 2 −C(CH 3 )═CH 2 ) 82−91 mol % and acceptable monomodal molecular weight distribution ( M w / M n = 1.7−2.3) could be successfully synthesized at low concentration of FeCl 3 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 −C H 3 of the growing chain ends and chain transfer reaction to monomer were dependent on concentration of iPr 2 O·FeCl 3 complex (1:1), concentration of free iPr 2 O ([free iPr 2 O] = [iPr 2 O] − [FeCl 3 ]) if (iPr 2 O·FeCl 3 > 1) and polymerization time. The much higher concentration of PIB chains formed in the polymerization system ( C PIB ) than that of components in initiating system indicates a chain-transfer dominated caionic polymerization process. To the best of our knowledge, this is the first example to achieve HRPIBs with such high exo -olefin end groups by FeCl 3 -based initiating system.