Abstract: A binary mixture of N, N-dimethylaniline(DMA) and benzyl chloride(BzCl), or ammonium salts of such compounds, are capable of initiating free radical polymerization reactions of vinyl monomers. Such initiating techniques had been employed for modifying cellulose through graft copoly-merization reactions. Further investigation was conducted on the initiative charactertics of such a system. A dilatometric method was used to measure the polymerization rate(Rp) of methyl methacrylate(MMA) (degassed under high vacuum) in benzene solvent at 60℃. Results obtained were as follows: and Rp∞[I], (when [DMA] = [BzCl] =[I]) Also, RP∞[BzCl]1/2, (when [DMA] = constant). The kinetic rate equation has been obtained: The effects of substituted groups at the benzene ring of DMA on the polymerization rate were also studied.It is found that when the electron-withdrawing groups were attached on the benzene ring of DMA, then the Rp of MM A initiated by them would drop down. The effects of such electron-withdrawing groups could be described by the Hammett equation.