A new radical initiator, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane (DMDEHPH), has been used to initiate styrene (ST) and methyl methacrylate (MMA) polymerization in the temperature range of 50-80 degrees C and DMDEHPH concentration range of 0.0050. 100 mol/L. The effects of initiator concentration, monomer concentration and reaction temperature on the polymerization rate were investigated in details. The increase of these three parameters will all increase the polymerization rate. The orders of polymerization rate to peroxide group concentration and monomer concentration were found to be 0.5 and 1.0, respectively, which validates the correctness of kinetic model derived from the mechanism of polymerization. The activity energy obtained from the polymerization rate constants at various temperatures is 92.0 kJ/mol for ST and 81.4 kJ/mol for MMA. The initiator efficiency is in the range of 0.55 +/-0.03 for ST and 0.43 +/- 0.02 for MMA under the experiment conditions. And the initiator efficiency decreases with the increase of initiator concentration. (c) 2005 Elsevier Ltd. All rights reserved.