Thermoelasticity of polymer networks

The thermoelastic properties of polymer networks are of interest owing to the information they provide on kappa = d ln <R-2> (0)/dT, the temperature coefficient of chain dimensions of the network species. Stress-strain measurements at constant volume provide that information directly, through a determination of the energetic fraction of the restoring force f(e)/f. Almost always, however, the measurements are conducted under constant-pressure conditions, and a correction is applied to account for the effect of volume change. The correction formula commonly used is known to be inaccurate, and here we present a new one that predicts the volume change and kappa quite satisfactorily. Some comparisons of kappa obtained from thermoelastic measurements, from small-angle neutron scattering, and from intrinsic viscosity data in athermal solvents are given.