Water-soluble urethane acrylate ionomers and their ultraviolet (UV) curing: Prevention of moisture absorption

Water-soluble and ultraviolet (UV)-curable urethane acrylate ionomers containing alpha,alpha-dimethylolpropionic acid (DMPA) were synthesized varying the molecular weight of the soft segment. In addition, their coating properties were also examined. When placed in the atmosphere for a long period, the tensile strength and the initial modulus of the UV-cured ionomer films decreased. Moreover, the disappearance of the ionic hard domains was observed by the dynamic mechanical analysis (DMA). These results indicated that the strong hydrophilicity of the ionomer network readily absorbed moisture in the atmosphere. However, by changing the stoichiometric mixing ratio of the urethane acrylate ionomer to the urethane acrylate not containing ionic groups, the moisture absorption of the ionomer network was successfully prevented. In DMA measurements, it was observed that the ionic hard domains did not disappear even in a comparatively long aging time (about 3 weeks). This could be achieved by the incorporation of the hydrophobic moiety in-to the hydrophilic ionomer network, which was induced by the urethane acrylate.