Responsive switches classification by their intrinsic structures: physical switch and chemical one.

Thermoplastic polyurethane composites (TPCs) in kilogram scale reinforced with monodispersed functionalized graphene (FGr) are prepared by melt-blending on industrial extruder and their properties are studied in this work. It shows that the saturation content of monodispersed FGr in TPCs is ≈0.5 wt%, beyond which part of it will agglomerate. The multiple effects of monodispersed FGr-micro-crosslinking, isolation, and induced crystallization-have great impact on the properties of TPCs. With the content increase of FGr, the melt rheological properties, crystallization properties, mechanical properties, and shape memory properties of TPCs show regular changes. More importantly, the tensile fracture behaviors of TPCs are dramatically changed by FGr. Some microfibers with high strength are formed and lay astride the cracks to prevent crack propagation during the damage process. Therefore, the tensile strength of TPC with 0.5 wt% FGr is maximumly improved, showing an increase of 139% compared to neat thermoplastic polyurethane. Its shape fixed ratio and shape recovery ratio are respectively raised to 96% and 94%, showing a good shape memory performance.

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Self-healing polyurethanes (PUs) with disulfide bonds and diphenyl silicon groups involved in the soft phases were prepared and studied in this work. The self-healing efficiencies of PUs are greatly improved by the synergistic effect of diphenyl silicon groups with low surface energy-increasing the distance between two polymer chains, enhancing the mobility of polymer chains, and promoting the migration of sulfur-containing groups to the damaged sites. The analysis of activation energy for the movement of polymer chains based on dynamic mechanical thermal analysis shows that, the higher contents of disulfide bonds and diphenyl silicon groups, the stronger mobility of polymer chains, and the higher self-healing performance of PUs. The study of temperature and time dependencies for the healing process at damaged sites indicates that it is composed of the recombination of disulfide bonds and the interpenetration and intertwining of polymer chains. The former can be completed in a shorter time, while the latter in a longer time. Sufficient time of heat treatment at relatively high temperature is necessary to get high self-healing efficiency. This strategy and the relative results are instructive to design and development of self-healing PUs.