Polymer gel electrolytes synthesized by photopolymerization in the presence of star-shaped oligo(ethylene glycol) ethers (OEGE)

The photoinitiated cross-linking polymerization of tri(ethylene glycol) dimethacrylate and its copolymerization with cyanomethyl methacrylate in the presence of LiCF3SO3 and of various oligo(ethylene glycol) methyl ethers as plasticizer was studied for potential use of the resulting polymer gel electrolytes in lithium batteries. Comparing linear and star-shaped (three and four arm molecules) oligo(ethylene glycol) methyl ethers, the influence of the architecture of the plasticizers on the polymerization course was investigated by means of differential scanning calorimetry. Linear and star-shaped plasticizers with molar masses < 1000 g/mol differ from each other concerning the dependence of their viscosity on their molar mass but not concerning the influence of the viscosity on the polymerization rate. Compared with linear plasticizers, the star-shaped ones have as an essential advantage a distinctly lower tendency to crystallize which is even completely suppressed in some cases. The gels were characterized with regard to the network density of their polymer matrix, to their thermal transitions, thermo-mechanical properties and ionic conductivity. The conductivity of solutions and gels with star-shaped plasticizers was slightly lower than that with linear ones at temperatures above room temperature.