The kinetics of photochemical polymerization of styrene (St) and methyl methacrylate (MMA) using a binary initiation system composed of poly( ethylene oxide) with an aniline end group (PEG(a)) and benzophenone (BP) was investigated by a modified dilatometer. The effect of the concentration of the monomer, BP and PEG(a), and of the molecular weight of PEOa on the polymerization rate (R-p) and conversion of monomers is discussed in detail. The formulas of R-p proportional to proportional to [PEOa](0.38) [St](0.33) [BP](0.56) and R-p proportional to [PE0(a)](0.36) [MMA](0.30) [BP](0.54) using benzene as a solvent are derived when the molecular weight of PEO is 11,000 (PEOa - 11,000). Compared with the small aminophenol (AP), there existed a critical PEOa concentration to affect the R-p and conversion of the monomers and the critical concentration is strongly dependent on the polarity of the solvents and molecular weight of PEOa. It is confirmed that in the same conditions the solution polymerization behavior of St and MMA initiated by the imino radical of PEO would not be affected by the properties of the second block although PMMA is miscible and PS is immiscible with PEOa in the bulk.