The reactions of living polyisobutylene (PIB+) with different allylsilanes, as potential linking and coupling agents, have been studied. Quantitative monoaddition of 2-Phenylallyltrimethylsilane to living PIB+ yielded macromonomer (I), however coupling was absent. Rapid and quantitative coupling has been observed with 1,3-bis[2-(3-trimethylsilyl)-propenyl]benzene (bTPB). Using 1-(2-propenyl)-3-[2-(3-trimethylsilyl)-propenyl]benzene (PTPB) star polymers with an average of four arms have been prepared with high efficiency. The study of this linking reaction revealed that star formation takes place in two well separated steps. In the first step a macromonomer is formed in situ by the rapid reaction of PIB+ with the allyltrimethylsilyl functionality. Subsequent reaction of this macromonomer with the remaining electrophilic PIB+ ends followed by interchain reactions results in the formation of star polymers.