Physical properties of some organophosphazene copolymers. I. Structural aspects, transition temperatures, and stress-strain isotherms of the cross-linked networks

Analysis of several poly(organophosphazene) copolymers with variedmeta- andpara-substituted phenoxy repeat units indicated that the copolymers had random sequences, with compositions very close to the equimolar feed ratios used in their synthesis. DSC measurements indicated that they were semicrystalline in spite of this randomness. Networks prepared by cross-linking these copolymers were studied in elongation above their melting points, and stress-strain isotherms thus obtained showed the presence of strain-induced crystallization. Raising the temperature decreased their values of the modulus, presumably by melting some of these crystallites. Swelling the networks also decreased their values of the modulus (at least partly because of solvent-induced depression of the melting point) and decreased their values of the elongation at rupture (presumably because of the stretching-out of the chains by the imbibed solvent prior to the elongation measurements).