Polysilane based block copolymers were prepared by photopolymerization using poly(methylphenylsilane) (PMPS) as photo-radical initiator. Effects of monomer type, UV intensity and PMPS/monomers mass ratio on polymerization kinetics parameters and block length were evaluated by the self-build kinetic modeling. These results were analyzed together with the phase separation observations. Since the average number of carbon atoms per structural block decreases to 5～6 and the average number of silicon atoms per structural block decreases to about 2 after 1000 s of polymerization, no phase separation occurs. The results indicate that they are potential materials for optical waveguide applications.