Catalyzed cationic polymerization within isobutylene clusters has been observed in the presence of Al+/(CH3)(3)CCl. The predominant reaction between Al+ and isobutylene clusters (C4H8)(n) involves simple clustering around the metal cation. Evidence for intracluster reactions within the Al+(C4H8)(n) clusters resulting in the formation of AlC2H3+ and AlCH3+ ions is also provided. In the presence of (CH3)(3)CCl, the carbonium ion h-C4H9+ is observed following the formation of AlCl. Several polymerization channels such as t-C4H9(C4H8)(n)(+), t-C4H9(C4H8)(n)(+)(ClAl), t-C4H9(C4H8)(n)(+)(ClC4H9), and t-C4H9(C4H8)(n)(+)(ClAl)(ClC4H9) have been observed. The role of ion pairs such as C4H9Cl and AlCl associated with the carbocation chain seems to increase the polarizability of the growing polymeric ion which could lead to enhancement of the propagation efficiency. Clusters provide a valuable and feasible approach for understanding the mechanism of cationic polymerization and how the size of the polymeric ions is controlled in such a process.