In this paper, penta-coordinated silicon compound with high reactivity was prepared by the reaction of silica with ethylene glycol and potassium hydroxide. This penta-coordinated silicon then reacted with allyl chloride to give a tetra-coordinated silicon monomer. The effects of conditions such as temperature, reaction time, reagent concentration, solvent and pH value on reaction were discussed. Then branch silicon copolymer between the tetra-coordinated silicon monomer and methyl methacrylate (MMA) was gained through the free radical solution polymerization using AIBN as an initiator. The structure of monomer was analyzed by the modern measuring methods, including FTIR, NMR (¹³C, ¹H and ²⁹Si), and elemental analysis of energy diffraction spectrum (EDS). The structure and thermal property of branch silicon copolymer were analyzed by IR, TG, DSC and GPC. The IR spectrum of tetra-coordinate silicon monomer indicated an absorption band for C＝C at 1646 cm^－1, but the copolymer exhibited no absorption band at 1646 cm^－1. TG analysis showed the copolymer began losing weight at 249.6 ℃ and ended at 550 ℃. GPC analysis displayed that the mo-lecular weight of the copolymer was 87000.

Key words: free radical solution polymerization, containing-silicon polymer, coordinated-silicon