Polyisobutylene-Based Thermoplastic Elastomers. IV. Synthesis of Poly (Styrene-block-Isobutylene-block-Styrene) Triblock Copolymers Usingn-Butyl Chloride as Solvent

The polymerization of isobutylene and styrene was studied using the 2-chloro-2,4,4-trimethylpentane/TiCl4 initiating system in the presence of a proton trap in halogenated hydrocarbons as solvents at −80°C. The polymerization of isobutylene was found to be living, and both homopolymers were soluble in n-butyl chloride. However, side reactions, namely polymerization by direct initiation and intra- and inter-molecular alkylation, are operational in the polymerization of St in n-butyl chloride. Polymerization by direct initiation can be minimized by increasing the initiator concentration, and intermolecular alkylation can be reduced by quenching the polymerization system when conversion reaches ∽ 100%. A careful selection of the experimental conditions was necessary to minimize intramolecular alkylation and obtain complete styrene conversion. Polystyrene-polyisobutylene-polystyrene triblock copolymers prepared under these conditions by sequential monomer addition in n-butyl chloride exhibited ∽ 24 MPa tensile strength, indicating the virtual absence of diblock contamination.