Abstract: PMMA-MA (MA: methacrylate)macromers (M_1) with different molecular weight were synthesized with radical polymerization and characterized with ~1H-NMR, VPO and sulphur analysis. The maeromers were copolymerized with styrene (M_2). The treatment with Kelen-T(?)d(?)s method of the copolymerization data obtained with GPC and gravimetric analysis indicate that Mayo-Lewis equation is invalid for this copolymerization system, while the equation r_2=1n(M_2_0/M_2)/1n(M_1_0/M_1) describes it according to analysis of the mechanism. With this equation, several values of r_2 were calculated out by using mean square regression, r_2 changes from 0.79 to 1.3 due to different reaction conditions, such as (?)_n and initial concentration of the macromers and the temperature. In this system exists an obvious diffusion factor. So r_2 increases as the diffusion process slows down.