A copolymer, poly-methyl methacrylate-vinyl acetate (PMMA-VAc), was synthesized by emulsion polymerization with methyl methacrylate (MMA) and vinyl acetate (VAc) as monomers. With this co-polymer, polymer membrane and polymer electrolyte were prepared on the basis of polyethylene membrane. Performances of the synthesized copolymer and prepared polymer membrane and electrolyte were studied with FTIR, GPC, DSC/TG, SEM and battery charging and discharging experiments. It was found from FTIR that PMMA-VAc was formed by breaking the double bonds of monomers. PMMA-VAc can be easily dis-persed in mixed carbonates to form a gel. The viscosity of the gel increases with the content of PMMA-VAc in carbonates, and the best content of PMMA-VAc for polymer membrane is 4%. PMMA-VAc copolymer has a porous structure, which has a good electrolyte absorptivity. It is stable up to 380 ℃. The conductivity of the polymer electrolyte at room temperature is 1.85×10^－3 S•cm^－1. With the polymer electrolyte as the gel polymer electrolyte (GPE) of battery Li/GPE/LiCoO₂, the battery shows its good cyclic stability and high rate discharge performance.

Key words: polymer electrolyte, PMMA-VAc, preparation, Li ion battery