Study on microstructure of UV-curable polyurethane acrylate films

UV-curable polyurethane acrylates (UVPUA) were prepared, and Fourier transform infrared (FTIR) was used to monitor the synthesis process and cured films. Effects of soft segment length, isocyanate type, reactive diluent type and level, quenching, annealing and different UV-cured degree on the microstructure of UVPUA films have also been studied. With soft segment length increasing, the degree of hydrogen bonding between soft segment and hard segments decreases, and microphase separation of UVPUA becomes better. Soft segment crystallization appears with its molecular weight exceeding 2000, when its value reaches 4000, an even more obvious melting peak in differential scanning calorimetry (DSC) curve was observed. Congregation of hard segment domains and the improvement of phase separation were due to symmetry and regularity of isocyanate, while rigid benzene ring was beneficial to crystallize and increase the glass transition temperature (Tg). The increased crosslink density with increasing the function degree of diluent resulted in better phase separation, on the contrary, increasing the reactive diluent content led to the opposite because of a phase reversion. Microphase separation lower during quenching and annealing due to post-curing of 1,6-hexa-nediol diacrylate (HDDA) at high temperature, and with the UV-cured degree increasing, the phase separation got better first and then became worse.