Kinetics of the Carbocationic Homopolymerization of Isobutylene with Reversible Chain Termination

Abstract

he kinetics of isobutylene (IB) polymerization, initiated by 2-chloro-2,4,4-trimethylpentane (TMPCI)/TiCI4 initiator/coinitiator system in methyl chloride/methyl/cyclohexane solvent mixture at −90°C, was investigated. The existence of a dynamic equilibrium between dormant and active species was verified by obtaining ‘living’ conditions and 100% initiator efficiency using a large excess of initiator over coinitiator [TMPCI]0 >> [I]4. It was shown that the polymerization rate is first order in monomer and is directly proportional to [TiCI4]0 and [TMPCI]0. From polymerization rate data the overall polymerization rate constant k′p=kpK1 was calculated, where kp is the rate constant of propagation and K1 = k1/k−1 is the equilibrium constant for the dormant-active species equilibrium. The rate of TMPCI consumption was shown to be first order in [TMPCI]. While polymer concentration increased during the rather slow initiator consumption, the polymerization rate did not accelerate as the concentration of active species, determined by the dormant-active species equilibrium, remained constant. From initiator consumption data k1 and kp/k−1 values were estimated. The estimated rate constant values were used to simulate monomer and initiator conversion histories versus time. The simulated histories were in good agreement with measured data.