High molecular weight poly(vinyl)silazane were synthesized successfully by reversible addition fragmentation chain transfer (RAFT) polymerization in toluene at 120 degrees C, using dithiocarbamate derivatives and 2,2'-azobis-isobutyrylnitrile (AIBN) as the RAFT agents and thermal initiator, respectively. The polymerization of a vinyl-cyclicsilazane oligomer with 82.5% conversion was readily controlled to increase the molecular weight from 1000 to 12,000 g/mol with a narrow polydispersity <1.5. The resulting polymer showed a high ceramic yield of 70 wt % at 1000 degrees C. Moreover, the approach was extended successfully to the synthesis of poly(vinyl)silazane-block-polystyrene as an inorganic-organic diblock copolymer. (C) 2008 Wiley Periodicals, Inc.