The 1,1-diphenylethene (DPE) controlled radical polymerization of methyl methacrylate was performed at 80 degrees C by using AIBN as all initiator and DPE as a control agent It was found that the molecular weight of polymer remained constant with monomer conversion throughout the polymerization regardless of the amounts of DPE and initiator in Formulation To understand the result of constant molecular weight of living polymers in DPE controlled radical polymerization, a living kinetic model was established in this research to evaluate all the rate constants involved in the DPE mechanism The rate constant k(2), corresponding to the reactivation reaction of the DPE capped dormant chains, was found to be very small at 80 degrees C (1 x 10(-5) s(-1)), that accounted for the result of constant molecular weight of polymers throughout the polymerization, analogous to a traditional free radical polymerization system that polymer chains were terminated by chain transfer The polydispersity Index (PDI) of living polymers was well controlled <1.5 The low PDI of obtained living polymers was due to the fact that the rate of growing chains capped by DPE was comparable with the rate of propagation (C) 2009 Wiley Periodicals, Inc J Polym Sci Part A. Polym Chem 47 6789-6800, 2009