We have developed a new strategy to prepare multiblock polymers and copolymers via one- or two-step polymerization using a polymerizable cyclic trithiocarbonate (CTTC), 4,7-diphenyl-[1,3]dithiepane-2-thione. CTTC undergoes ring-opening process to incorporate a trithiocarbonate moiety. The trithiocarbonate moiety in turn, functions as a reversible addition fragmentation chain transfer (RAFT) agent. Through this mechanism, multiblock polystyrenes and polystyrene-block-poly(butyl acrylate) copolymers containing various narrow polydispersity blocks can be prepared.