AbstractThe rate of photochemical polymerization of styrenc (St) and methyl methacrylate (MMA) with polymcthylphenylsilane (PMPS) as initiator were measured. Polymethylphenylsilane is photodegraded to form silyl radicals that may initiate polymerization of St and MMA. The kinetic orders of polymerization reactions of initiator PMPS in St and in MMA systems are 0.49 and 0.29, respectively. The rate coefficients kpand ktare 38.1 and 0.71 × 107Lmol‐−1s−1in the St/PMPS system and 249.5 and 6.71 × 107Lmol−1s−1in the MMA/PMPS system. A polymerization reaction mechanism