Gel electrolyte films were prepared from oligo(ethylene glycol) dimethacrylate ((EG)(n)DMA, n = 23) and cyanomethyl methacrylate (CyMA) by photoinitiated in situ copolymerization in the presence of oligo(ethylene glycol) dimethylether ((EG)(n)-DME, n = 11) and LiCF3SO3. The influence of the content of CyMA in the copolymer on the ionic association of LiCF3SO3 as well as on the thermal and electrochemical properties of the gels was studied. About 80mol% CyMA in the copolymer network causes a relatively high dissociation degree of LiCF3SO3 (approximate to 50%), cationic transference numbers t(+)approximate to 0.5 and an anodic stability up to 5V. The ionic conductivity a shows a maximum around 20 mol% CyMA attaining sigma x 10(-4) S/cm at ambient temperature. The decrease of sigma at higher contents of CyMA in the crosslinked polymer is attributed to the insertion of substantial parts of (EG)(11)DME into the copolymer network and to a chain stiffening effect of CyMA.