Influence of molecular architecture on the isothermal time-dependent response of amorphous shape memory polyurethanes

The thermomechanical response of a series of thermally activated shape memory polyurethanes (SMPUs), determined by dynamic mechanical analysis (DMA), has been adjusted by systematic modification of the molecular architecture. It is argued that the free recovery behavior of these SMPUs at temperatures in the vicinity of the calorimetric glass transition temperature is dependent not only on the recovery temperature, but also on the form of the corresponding peak in tan δ in DMA temperature scans at constant frequency. On the basis of simple correlations between recovery rates and the width and shape of the tan δ peak, it is suggested that DMA may provide a relatively simple and rapid means of assessing the potential of the SMPUs with respect both to recovery and shape fixity at a given storage temperature. This in turn allows establishment of a direct link between the shape memory performance and molecular architecture.