The thermal and thermomechanical properties of two series of poly(ethylene oxide) networks (NPEOs) were investigated as a function of the chain length between crosslink sites (M-c) and the concentration of LiClO4 (C-L) in the NPEOs. The two series of networks were produced with silica and organic crosslinking agents and, therefore, had crosslink sites of different natures: one was an inorganic silicate network (silica NPEO), and the other was an organic polar group (organic NPEO). The crosslink sites in both series of networks were commonly covalently bonded to the poly(ethylene oxide) (PEO) phase through a urethane group in the NPEOs. The glass-transition temperatures (T-g ' s) of the PEO phases in the NPEOs, according to differential scanning calorimetry, increased with a decrease in M, and were higher in the silica NPEOs than in the organic NPEOs under the same M, conditions. The difference in T between the two series of networks with the same M, values increased with decreasing M,. These results suggested that the interaction of crosslink sites with the PEO phase was stronger in the silica NPEOs than in the organic NPEOs. The addition of LiClO4 to the NPEOs resulted in T-g of the PEO phase in the NPEOs being elevated and increased according to the increase in C-L The increase of T-g of the PEO phase according to the increase of C-L in the NPEOs was retarded or saturated at high values of C, and this indicated that the limit of solubility of the salt in the polymer was attained. The retardation or saturation of the increase of T-g was also observed in dynamic mechanical analyses. Thecurves of the loss factor tan 5 and temperatures from the dynamic mechanical analyses for the NPEOs with high values of C, showed shoulders or double peaks indicating the existence of the second phase in the polymer networks. In the curves of tan 5 for salt-complexed NPEOs with high values of C-L silica NPEOs showed a shoulder of low intensity, but organic NPEOs showed a distinguished second peak becoming stronger with increasing C-L. The results of the T behavior and tan 6 curves suggested that the salt solubility in the NPEOs was limited and that the salt solubility of PEO in the silica NPEOs was higher than that in the organic NPEOs. (C) 2003 Wiley Periodicals, Inc.