The cationic ring-opening polymerization of octamethylcyclotetrasiloxane initiated by R(3)SiH-Ph(3)C(+)B(C6F5)(4)(-) (trityl TPFPB) in the absence of protic acids has been investigated. Mechanistic studies demonstrate that the polymerization proceeds by a single "long-lived" oxonium ion end. This novel polymerization is distinct from those initiated by protic acids. Cyclotrisiloxanes containing vinyl or trifluoropropyl groups could be polymerized in a similar manner, while the homopolymerization of trimethyltriphenylcyclotrisiloxane failed. The method has also been extended to the preparation of siloxane-containing diblock copolymers and comblike branched polysiloxanes.