Gel polymer electrolytes composed of methyl methacrylate-styrene copolymers (PMS) and electrolyte solution (LiTFSI in EC/DMC) were prepared and characterized. Depending on the molar composition of the copolymer, these gel polymer electrolytes exhibited different electrochemical and mechanical properties. In order to investigate the physical interactions among organic solvents, polymer, and lithium ions occurred in the gel polymer electrolyte, Raman spectroscopy and solid state 7Li NMR spin–spin relaxation measurements were performed.