Preparation of waterborne polyurethane film based on spirooxazine containing hydrophilic groups

The problem of poor compatibility between organic functional molecules and waterborne polyurethane systems has received widespread attention. Herein, in order to reduce the effect of spirooxazine introduction on the compatibility of polyurethane in aqueous systems, two novel spirooxazine compounds SO2 and SO4 with hydrophilic groups were synthesized and successfully introduced into waterborne polyurethanes by chemical bonding and physical blending. The results show that compared with pure waterborne polyurethane, the particle size of the waterborne polyurethane emulsion bonded with SO2 or SO4 (0.5 wt%) is significantly reduced, and the SO4 effect is more obvious. Therefore, SO2(0.5)-WPU (grafted with 0.5 wt% SO2) and SO4(0.5)-WPU (grafted with 0.5 wt% SO4) have more uniform film formation and higher light transmittance. Additionally, the physical blending of SO2 and SO4 has less impact on the mechanical properties and water resistance of the films compared to chemical grafting. Tensile strength was able to maintain 72.3% and 88.5%, and water resistance remained 77.5% and 68.5%, respectively. The films prepared by the two methods have good photochromic performance and fatigue resistance, but the spirooxazine in the chemically bonded film has better thermal stability. Therefore, we provide a new idea for the preparation of functional aqueous polyurethane.