A metal complex, cobalt(II) 2-ethylhexanoate (CEH), was added to the system of thermal-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) with 2-cyanoprop-2-yl 1-dithionaphthalate (CPDN) as the RAFT agent at 115 degrees C. The polymerization rate was remarkably enhanced in the presence of CEH in comparison with that in the absence of CEH, and the increase of the CPDN concentration also accelerated the rate of polymerization. The polymerization in the concurrence of CPDN and CEH demonstrated the characters of '' living ''/controlled free radical polymerization: the number-average molecular weights (M-n) increasing linearly with monomer conversion, narrow molecular weight distributions (M-w/M-n) and obtained PMMA end-capped with the CPDN moieties. Meanwhile, CEH can also accelerate the rate of RAFT polymerization of MMA using the PMMA as macro-RAFT agent instead of CPDN. Similar polymerization profiles were obtained when copper (I) bromide (CuBr)/N,N,N',N '',N ''-pentamethyldiethylenetriamine was used instead of CEH. Extensive experiments in the presence of butyl methacrylate, bis(cyclopentadienyl) cobalt(II) and cumyl dithionaph-thalenoate were also conducted; similar results as those of MMA/CPDN/CEH system were obtained. A transition of the polymerization mechanism, from RAFT process without CEH addition to atom transfer radical polymerization in the presence of CEH, was possibly responsible for polymerization profiles. (c) 2007 Wiley Periodicals, Inc.