ASPECTS OF THE SYNTHESIS OF POLY(STYRENE-B-ISOBUTYLENE-B-STYRENE) BLOCK-COPOLYMERS USING LIVING CARBOCATIONIC POLYMERIZATION

The effect of the time of styrene addition on the composition of poly(styrene-isobutylene-styrene) (PS-PIB-PS) block copolymers synthesized using a dicumyl chloride/TiCl4/pyridine initiating system and the sequential addition of monomers was investigated at -800-degrees-C. It was found that the addition of styrene at an isobutylene (IB) reaction time significantly exceeding the time necessary for complete IB consumption results in contamination of the material with a substantial amount of homo-PS. Conversely, the addition of styrene to PIB chains formed under conditions of intermediate IB conversion resulted in a very slow buildup in molecular weight after the addition of styrene. This retardation of the rate after the addition of styrene was proven to be the result of a random copolymerization between styrene and unreacted IB. It was also found that the addition of the proton trap 2,6-di-tert-butylpyridine resulted in a narrowing of product polymer molecular weight distribution.