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

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 (T_p) 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 T_p 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 (M_w/M_n = 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