We have investigated the thermal and ionic conductivity properties of the elastomer poly(ethylene oxide-co-epichlorohydrin) filled with NaI and I-2. The reason for using this composition is its potential application as electrolyte in photoelectrochemical cells. This copolymer was characterized as a function of NaI concentration, temperature and relative humidity. According to the data obtained, the Na+ ion interacts with the ethylene oxide repeating units by means of Lewis type acid-base interactions. The empirical Vogel-Tamman-Fulcher equation was used to model the conductivity and temperature relationships, indicating that the conduction occurs in the amorphous phase of the copolymer. The sample with 9.0% (w/w) of NaI presents a conductivity of 1.5 x 10(-5) S cm(-1) in a dry atmosphere (30 degreesC, [H2O] < 1 ppm) and 2.0 X 10(-4) S cm(-1) at 86% relative humidity (22<degrees>C). (C) 2001 Elsevier Science B.V. All rights reserved.14041732327335