Star-shaped polymers of isobutyl vinyl ether (IBVE) with a microgel core of an aliphatic divinyl ether (2) were synthesized in high yield on the basis of the living cationic polymerization with the HCl/ZnCl2 initiating system. GPC analysis demonstrated that linear coupling products ("two-armed" polymers) and three-armed star polymers formed during the early stages of the linking reaction, and that subsequent coupling reactions between such low molecular weight star polymers gave star-shaped polymers with more arms. The number of arms ranged from 5 to 22, which increased with increasing [2](0)/[P*] ratio and/or shortening the arm chain.