LIVING CARBOCATIONIC SEQUENTIAL BLOCK COPOLYMERIZATION OF ISOBUTYLENE WITH ALPHA-METHYLSTYRENE

The polymerization of alpha-methylstyrene (alpha MeSt) was investigated using the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl4/methyl chloride:hexane (40:60, v:v)/-80 degrees C system as a model to determine the efficiency of crossover from Living polyisobutylene (PIE) to alpha MeSt. Low initiator efficiencies and broad molecular weight distributions were obtained. Living polymerization of alpha MeSt was achieved by first converting TMPCl to the corresponding diphenylalkylcarbenium ion by capping with 1,1-diphenylethylene (DPE), followed by the addition of titanium(IV) alkoxide to decrease the Lewis acidity. The initiator efficiencies, however, were lower than 100%. Living polymerization with similar to 100% initiator efficiency was achieved by SnBr4 as coinitiator. First, TMPCl is transformed to the corresponding diphenylalkylcarbenium ion by capping with 1,1-diphenylethylene. Subsequently, titanium(IV) isopropoxide is introduced to deactivate TiCl4, followed by the addition SnBr4 and alpha MeSt. The success of the method was demonstrated by the synthesis of PIB-poly(alpha-methylstyrene) diblock copolymers without homopolymer contaminants.