Synthesis of highly reactive polyisobutylenes with exo-olefin terminals via controlled cationic polymerization with H2O/FeCl3/iPrOH initiating system in nonpolar hydrocarbon media

Abstract

Cationic polymerizations of isobutylene (IB) with H2O/FeCl3/isopropanol (iPrOH) initiating system were conducted in nonpolar hydrocarbon media, such as n-hexane or mixed C4 fractions at −40 to 20 °C. This cationic polymerization is a chain-transfer dominated process via highly selective β-proton elimination from CH3 in the growing chain ends, leading to formation of highly reactive polyisobutylenes (HRPIBs) with large contents (> 90 mol %) of exo-olefin end groups (structure A). The content of structure A remained nearly constant at about 97 mol % during polymerization and isomerization via carbenium ion rearrangement could be suppressed in nonpolar media. First-order kinetics with respect to monomer concentration was measured for selective cationic polymerization of IB in the mixed C4 fraction feed at −30 °C and the apparent rate constant for propagation was 0.028 min−1. High polymerization temperature (Tp) or [FeCl3] accelerate β-proton elimination or isomerizations and simultaneously decrease selectivity of β-proton abstraction from CH3. Molecular weight decreased and molecular weight distribution (MWD) became narrow with increasing Tp or [FeCl3]. To the best of our knowledge, this is the first example to achieve high quality HRPIBs with near 100% of exo-olefin terminals and relatively narrow MWD (Mw/Mn = 1.8) by a single-step process in nonpolar hydrocarbon media. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4200–4212