Mechanical properties of amphiphilic urethane acrylate ionomer hydrogels having heterophasic gel structure

Amphiphilic urethane acryale hydrogels containing ionic groups (dimethylolp ropionic acid) were prepared by varying the molecular weight of the soft se gment (polyether type) and the type of diisocyanate, and their mechanical p roperties were examined. They showed heterophasic gel structure composed of ionic hard domains induced by aggregation of the ionic groups and polyethe r soft domains comprising the urethane acrylate network. This heterophasic structure could be confirmed by dynamic mechanical analysis (DMA) and by wi de-angle X-ray scattering analysis (WAXS); the crystallinity detected by WA XS and the transition peak of the ionic hard domains detected by DMA strong ly suggested that there were ionic aggregates. These ionic aggregates acted as reinforcing fillers in the network, which eventually enhanced the tensi le strength of the hydrogels. Above all, the tensile properties of the hydr ogels were of interest in that the trends of the stress-strain curves were consistent with the rubbery ones. It is believed that the higher purity of the polyether soft domains resulted from the heterophasic gel structure imp arting further elastomeric properties on the network.