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 ( 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 [ABSTRACT FROM AUTHOR]