Kinetic study of the living cationic polymerization of isobutylene using t‐Bu‐m‐DCC/TICL4/2,4‐dimethylpyridine initiating system

Abstract

AbstractKinetics of the living cationic polymerization of isobutylene, initiated by the system t‐bu‐m‐DCC/TiCl4/2,4‐dimethylpyridine (2,4‐DMP), were studied as a function of concentration of the various components of the initiation system, solvent polarity, and presence of the protic acid scavenger, 2,6‐di‐tert‐butylpyridine (DTBP). Under a variety of conditions, the effective number of growing chains in a given polymerization remained constant and Mn increased linearly with monomer conversion. The system was found to yield an essentially homogeneous reaction mixture in hexanes/methyl chloride cosolvents, with only a small amount of precipitate, probably 2,4‐dimethylpyridinium salts resulting from proton scavenging by the tertiary amine. It was found that increasing [TiCl4] strongly increased the rate while increasing [2,4‐DMP] weakly decreased the rate. Evidence of a retardation of the polymerization rate by the soluble TiCl4:2,4‐DMP complex was observed. The addition of DTBP as a protic acid scavenger, with or without 2,4‐DMP, very weakly decreased the rate of polymerization. Increasing the fraction of methyl chloride in the solvent mixture caused an increase in the rate of polymerization. All of the results were consistent with a propagation mechanism in which an equilibrium exists between dormant and ionized, active chain ends.