Study on the solar photocatalytic polymerization of methyl methacrylate in aqueous medium of TiO2／Na2SO3 system is given．Reaction system composed of iOH+2

Na2SO3

MMA and deionized water is carried out under constant temperature

solar shining

closed air atmosphere and without shaking．Results show that the initiation period τ is about 2～15 min and mainly depends on the pH value in the system．No initiation period when pH＜6.3．While at the pHzpc of nanometre TiO2(6.3＜pH＜6.7)·SO-3 free radicals produced on the Ti—h+vb—OH initiate the polymerization of MMA and a high yield (95％) with 1.2×106 molecular wight appears at the pH (6.9～7.O) with the decreasing H+ on the Ti—e-cb—OH．However the increasing·OH free radical results in the lower yield at alkaline pH．The apparent rate of polymeriation Rp=k·e-114.800/RT·[MMA]0.94[IA]0.50 [Na2SO3]0.55[TiO2]1.06 in the range of [MMA]=(3.74～10.7)×10-2mol·L-1[Na2SO4]=(1.0～1.56)×10-3mol·L-1 and[TiO2]=(5.0～7.0)×10-5 mol·L-1

similar results were obtained

when using powder TiO2(10～20 nm) to substitute the hydrated TiO2．