Polymer gel electrolytes were prepared by thermal crosslinking reaction of a series of acrylic end-capped poly(ethylene glycol) and poly(propylene glycol) [P(EG-co-PG)] having various geometries and molecular weights. Acrylic end-capped prepolymers were prepared by the esterification of low molecular weight (M-n: 1900-5000) P(EG-co-PG) with acrylic acid. The linear increase in the ionic conductivity of polymer gel electrolyte films was observed with increasing temperature. The increase in the conductivity was also monitored by increasing the molecular weight of precursor polymer. Nanocomposite electrolytes were prepared by the addition of 5 wt % of organically modified layered silicate (montmorillonite) into the gel polymer electrolytes. The enhancement of the ionic conductivity as well as mechanical properties was observed in the nanocomposite systems. (C) 2003 Wiley Periodicals, Inc.