Thermal behavior was examined using DSC and TG for the samples prepared by dissolving LiClO4 in several polyoxyethylene/polyethylenimine (PEO/PEI) blends (7/3-9.5/0.5 by repeat units) along with their lithium ion conductivity. Concerning the matrix polymers, while the pristine PEO and PEI began to thermally decompose at 185 and 230 degreesC, respectively, the (8/2) PEO/PEI blend had lost only 6.5% of its weight before 300 degreesC was reached. Dissolution of LiClO4 made the systems thermally even more robust: [(8/2) PEO/PEI](10)-LiClO4 suffered practically no weight loss below 300 degreesC. So far [(8/2) PEO/PEI](10)-LiClO4 has been our best-behaving SPE (c = 2.2 x 10(-4) S cm(-1) at 77 degreesC and 2.5 x 10(-6) S cm(-1) at 30 degreesC): it is less conductive than a previously reported PEO12-LiClO4 by a factor of 2.2 at 77 degreesC, but its conductivity drop due to the matrix crystallization below 65 degreesC is considerably milder and the conductivity at 30 degreesC was ca. 100 times higher than the plain PEO-LiClO4 systems. A significant effect of the residual methanol on the ionic conductivity of our [(8/2) PEO/PEI](10)-LiClO4 samples was recognized, which necessitated our previously reported log sigma vs. 1000/T curve to be corrected downward by ca. half an order of magnitude. (C) 2003 Elsevier Science Ltd. All rights reserved.