Substituted cyclotriphosphazenes were used to prepare lithium ion conducting polymer networks. Two types of compounds were synthesized starting with the precursor hexachlorocyclotriphosphazene (HCCP): Type I (CVEEP) in which all the chlorine atoms in HCCP were replaced by vinyloxyethoxyethoxy groups (VEE=-OCH2CH2OCH2CH2OCH=CH2), and type II (CVMEEP) in which half of the chlorine was replaced by VEE and the other half by methoxyethoxyethoxy groups (MEE=-OCH2CH2OCH2CH2OCH3). The terminal vinyl groups were used to build up a network by a thermally initiated cross-linking of lithium salt containing membranes. Polymer electrolytes with dissolved LiSO3CF3 and LiN (SO2CF3)(2) were investigated by impedance measurements. The ionic conductivity of CVMEEP with 10 wt.% LiSO3CF3 was 3.2 x 10(-5) S/cm at 30 degrees C and 4.1 x 10(-4) S/cm at 90 degrees C. Lower conductivity values in the range 10(-8)-10(-9) S/cm were obtained at 30 degrees C for the highly crosslinked CVEEP. An interesting polymer electrolyte with good mechanical properties and a good conductivity of 1.3 x 10(-5) S/cm (30 degrees C) was obtained from a solution of MEEP (=poly[bis(methoxy-ethoxy-ethoxy)phosphazene]) and LiSO3CF3 in CVEEP as an interpenetrating network. (c) 2006 Elsevier B.V. All rights reserved.