Living Carbocationic Polymerization ofp-Methylstyrene and Sequential Block Copolymerization of Isobutylene withp-Methylstyrene

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Abstract
A novel scheme was developed for the synthesis of pure polyisobutylene-poly(p-methylstyrene) block copolymers by sequential monomer addition. The synthesis involves the living polymerization of isobutylene by the TiCl4/methyl chloride:methylcyclohexane or hexanes 40:60 v:v/ -80°C system in the presence of di-tert-butylpyridine. When the polymerization of isobutylene is complete, the living polyisobutylene chain end is transformed to the corresponding diphenyl alkyl end by capping with 1,1-diphenylethylene. Subsequently, titanium(IV) isopropoxide or titanium(IV) butoxide is added to decrease the Lewis acidity followed by the addition of p-methylstyrene. The success of the method was demonstrated by p-methylstyrene homopolymerization experiments initiated by 2-chloro-2,4,4-trimethylpentane that resulted in ∼ 100% initiator efficiencies when the TiCl4/titanium(IV) isopropoxide or -butoxide ratio was less than 25/7, as well as by the clean synthesis of polyisobutylenepoly(p-methylstyrene) diblock copolymers.