In an effort to prepare a poly(vinylidene fluoride)-hexafluoropropene (PVdF-HFP) based polymer gel film electrolyte with higher mechanical strength and little volatility, a two component urethane system employing blocked multiisocyanate as a potential thermal crosslinking agent, and low molar mass poly(ethylene glycol) (PEG) as a hydroxy-functional coreactant was blended with the PVdF-HFP gel system, and the cure of the blends was examined as a function of temperature, molar mass of PEG, and PEG/blocked isocyanate ratio. The network forming reaction could not proceed below 100 degreesC, but it slowly took place above 120 degreesC by thermal deblocking of blocked multiisocyanate, followed by the reaction of regenerated free multiisocyanate with PEG in the absence and presence of PVdF-HFP, plasticizer (propylene carbonate, PC) and lithium perchlorate. The adduct of polymeric methylene diphenyl diisocyante (PMDI) with acetone oxime was used as a potential thermal crosslinking agent for this study. Network polymer gels having no PVdF-HFP were also prepared for comparison. The cured (PVdF-HFP/PEG/blocked PMDI/PC/LiClO4) polymer gel networks were mechanically and dimensionally stable, and their thermal characteristics and electrochemical properties were investigated using FT-IR spectroscopy, differential scanning calorimetry, electrochemical impedance spectroscopy and linear sweep voltammetry. (C) 2003 Elsevier Ltd. All rights reserved.