Thermoelasticity of the poly(2-hydroxyethyl methacrylate) gel

Anomalous thermoelastic behaviour has been reported by Warren and Prins for water swollen gels of poly(2-hydroxyethyl methacrylate) (PHEMA) subjected to simple tension. The central feature of the assertion that the molecular deformation mechanism in this polymer differs radically from that of all other known long range elastomers has been the claim that the entropic component of the tensile load is negative (fs < 0; fe f > 1) for certain temperatures in the range 30°-80°C. The experiments described here utilize a new technique to demonstrate, conversely, that the elasticity of the PHEMA gel is conventionally rubber-like in displaying a decrease in entropy on stretching. While confirming the similarity between PHEMA and other polymeric elastomers in this respect we note, however, an unusually large energy contribution to the tensile load ( fe f = 0.78) which distinguishes PHEMA from all other elastomers for which the energy component of force has been measured. It is suggested that the hydrophilicity of the PHEMA molecule may account for this. © 1977.