PHYSICAL AGING OF REACTION-CAST ACRYLATE AND METHACRYLATE POLYMERS AND OTHER DIMENSIONAL INSTABILITIES MANIFEST IN THERMOMECHANICAL ANALYSIS

Dimensional changes of acrylate and methacrylate polymers, networks an d hydrogels quenched from above the glass transition in liquid nitroge n were followed by thermomechanical analysis as the samples were rehea ted at a controlled rate. All except the more heavily cross-linked sam ples exhibited physical ageing effects and contracted as the glass-tra nsition region was approached. The magnitude of the fractional bulk co ntraction, f, depended on the range of accessible conformations availa ble to the system above T(g). The effects of number and length of side -chains and cross-links, compression-induced orientation, molar mass, plasticizers, anti-plasticizers and water (in hydrogels) were investig ated. It is concluded that the magnitude off depends on the range of a ccessible conformations available to the system above T(g) and is a re asonable indication of the fractional free volume prior to quenching.