Modified ultraviolet-curable water dispersible polyurethane-acrylates

Three kinds of UV-curable self-emulsified polyurethane-acrylate (PUA) prepo lymer, i.e., conventional, chain extended and grafted PUAs, were prepared. The relatively small particle size of the PUA dispersions indicates that th e PUA prepolymers exhibit sufficient aqueous dispersibility. The PUA prepol ymers can substantially lower the interfacial tension of water. Chain-exten ded PUA dispersions exhibit pseudoplastic behavior and thixotropy to a grea ter extent than do their conventional counterpart. The chain-extended and g rafted PUA photocure to higher conversion than do the conventional PU equiv alent. The results of DSC measurement suggest that there exists phase mixin g between the hard and the soft segment phases for the PUAs based on PEG 40 0 that is the comparatively short soft segment in the prepolymer. For the P UA prepolymers based on PEG having higher M-n values, chain-extending and g rafting could impede the phase separation between the hard and the soft seg ment domains. The adhesion, impact strength and flexibility of the photocur ed films were tested.