Tunable stress transfer efficiency of polyurethane to spiropyran by multi‐functionalization and its effects on mechano‐chromic response
Fangfang Zhang, Rong Ji, Nannan Sun, Jian Xu, Xu Zhang, Xiaoli Song, Junliang Liu, Ming Zhang, Shiping Zhang, Niu L
Abstract
Abstract Spiropyran (SP) derivatives with different hydroxyl groups have been synthesized and incorporated with polyurethane (PU) to prepare mechano‐chromic composites. With the content of hydroxyl groups in SP increasing, the stress transfer along PU molecular chain to SP have been effectively enhanced, resulting in the refined mechano‐chromic response. The correlation coefficient between mechano‐chromic efficiency and effective stress has been defined, which increased by using bishydroxyspiropyran (SP 2 ) instead of SP. With an optimized SP 2 content of 1.5 wt%, the composites demonstrated the improved mechano‐chromic effect and mechanical properties. The double hydroxyl groups in SP 2 grasped the PU chain in form of chemical bonding, leading to construction of micro‐phase structures in PU matrix.