The microwave-assisted synthesis of high molecular weight polyvinylsilazane (H-PVSZ) leads to a narrow molecular weight distribution at accelerated polymerization rates under controlled/living polymerization, while retaining the excellent controllability offered by reversible addition fragmentation chain transfer (RAFT) polymerization in a thermal reaction process. Under microwave irradiation, higher molecular weight H-PVSZ (6250 vs. 4370) was obtained with higher conversion (86.7 vs. 30.1%) than under conventional heating through a simple 3 h reaction of vinylcyclicsilazane with a molecular weight of 314 in the presence of dithiocarbamate derivatives (RAFT agent) and 2,2'-azobis-isobutyronitrile (AIBN, thermal initiator). H-PVSZ with a well-controlled high molecular weight is useful for synthesizing inorganic-organic diblock copolymer polyvinylsilazane-block-polystyrene (PVSZ-b-PS) with a higher molecular weight and lower polydispersity than by conventional heating of the PVSZ-derived product. (C) 2009 Elsevier Ltd. All rights reserved.