SYNTHESIS AND CHARACTERIZATION OF LINEAR AND 3-ARM STAR RADIAL POLY(STYRENE-B-ISOBUTYLENE-B-STYRENE) BLOCK-COPOLYMERS USING BLOCKED DICUMYL CHLORIDE OR TRICUMYL CHLORIDE/TICL4/PYRIDINE INITIATING SYSTEM

Linear and three-arm star styrene-b-isobutylene-b-styrene block copolymers were synthesized by living cationic polymerization using ring-substituted di- or tricumyl chloride, respectively, as initiator, TiCl4 as coinitiator, pyridine as an electron donor and 2,6-di-tert-butylpyridine as a proton trap in a 60/40 (v/v) methylcyclohexane/methyl chloride solvent mixture at -80-degrees-C. The polymers had equivalent compositions and segmental molecular weights allowing the effect of molecular geometry on sample morphology and physical properties to be determined. The samples exhibited a dual-phase morphology consisting of cylindrical polystyrene domains dispersed within a matrix of polyisobutylene; polymer geometry was found to have a significant effect on the tensile properties, with the three-arm star sample displaying a tensile strength twice that of the linear sample. In addition, the three-arm star block copolymer was found to have a higher rubbery plateau modulus than the linear block copolymer. Due to their perfectly saturated mid-block, polyisobutylene-based block copolymers were found to be much more thermally stable than the closely related styrene-b-(ethylene-co-1-butene)-b-styrene block copolymers (hydrogenated polybutadiene centre block).