Synthesis of highly reactive polyisobutylene by selective polymerization with o‐cresol/AlCl3 initiating system

Abstract

AbstractHighly reactive polyisobutylenes (HRPIBs) with very large proportion (up to 95 mol%) of exo‐double bond end groups and number average molecular weight (Mn) of 5400–8500 Dalton (Da) could be successfully synthesized by the selective cationic polymerization of isobutylene (IB) from the mixed C4 fraction feed using o‐cresol/AlCl3 as initiating system at −20°C. A possible mechanism was proposed for the cationic polymerization process. The presence of large weakly coordinating counteranion in propagating species could lead to decreasing the possibility of the side transfer reactions via carbenium ion arrangements. This o‐cresol/AlCl3 initiating system exhibited extremely high selectivity toward IB polymerization in the mixed C4 fraction feed and a good property for rapid β‐proton abstraction from CH3 in the growing polyisobutylenes (PIBs) chain ends. High extent of α‐double bond end groups in HRPIBs prepared in the mixed C4 fraction feed could be comparable to that in those commercially produced by cationic polymerization of IB in inert solvent (e.g. hexane). To our knowledge, this is the first example to achieve HRPIBs via completely selective polymerization of IB from C4 mixed feed with AlCl3‐based initiating system, providing a potentially practical process for its simplicity and low costs. Copyright © 2011 John Wiley & Sons, Ltd.