Polyisobutylene-based thermoplastic elastomers .4. Synthesis of poly(styrene-block-isobutylene-block-styrene) triblock copolymers using n-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 degrees 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 intermolecular 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 similar to 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 similar to 24 MPa tensile strength, indicating the virtual absence of diblock contamination.