Examination of Models for Carbocationic Polymerization: Influence of Chain Length on Carbocation Reactivities

The kinetics of the reactions of the carbocations CH 3 [C(CH 3 ) 2 CH 2 ] n C + Ph 2 ( 1a + − 1d +, n = 0, 1, 2, 34) with allyltrimethylsilane ( 4 ) and dimethylphenylsilane ( 5 ) have been investigated. It is found that the carbocation 1a + ( n = 0) is 10 2 times more reactive than the more highly substituted analogues 1b + − 1d +, which hardly differ in their electrophilic reactivity. We, therefore, conclude that the (CH 3 ) 3 CCH 2 and (CH 3 ) 3 CCH 2 C(CH 3 ) 2 CH 2 groups are suitable to mimic the polyisobutylene chain in a growing carbocation.