Cross-linked copolymers have been prepared by free-radical photoinitiated polymerization of dimethacryloxypropyl oligodimethylsiloxane with monomethacryloxypropyl oligodimethylsiloxane and the polar comonomers cyanomethyl methacrylate, cyanoethyl methacrylate, trifluoroethyl methacrylate and hexafluoroisopropyl acrylate, respectively, for use as a plasticizer-free membrane matrix for ion-selective sensors. The polymerization course in dependence on the composition of the monomer mixture and on the presence of ionophore and ion conducting salt as well as chloroform as solvating agent was studied by means of differential scanning calorimetry. The resulting copolymer membranes were characterized concerning the content of residual C=C double bonds and sol as well as their thermo-mechanical and electroanalytical properties. The thermal and mechanical properties of these copolymer membranes exhibiting a heterogeneous network structure are adjustable in a wide range by variation of the ratio of the monomers used. In comparison with the most widely used poly(vinyl chloride) based membranes containing a plasticizer, the K+ and Ca2+ selective sensor membranes based on the new copolymers exhibit analogous or even better electro-analytical properties and above all, a distinctly longer lifetime. (C) 2004 Published by Elsevier Ltd.