Trityl terminated poly(butyl vinyl ether) was obtained by the polymerization of butyl vinyl ether with triphenylcarbonium tetrafluoroborate-thiolane initiator system. In this system, thiolane was used to prevent both hydride abstraction of trityl cation and chain transfer of growing chain of butyl vinyl ether cation. Trityl terminated polymers served as thermal initer for the polymerization of methyl methacrylate which proceeded via a quasi-living radical mechanism. This procedure makes it possible to prepare block copolymers.