To further understand effects of titanium dioxide (TiO 2) nanoparticles on thermal, optical, microstructural, interfacial and mechanical properties of shape memory polyurethane (SMPU), TiO 2 /SMPU nanocomposites with different TiO 2 contents were synthesized. Then various properties of TiO 2 /SMPU nanocomposites were characterized. Results indicate that the melting temperature of soft segments in SMPU can be used as the shape memory transition temperature of TiO 2 /SMPU nanocomposites. TiO 2 nanoparticles are almost filled in SMPU pores to form compact skeleton structures in TiO 2 /SMPU when the TiO 2 content is 3% by weight. Further, the used TiO 2 is rutile phase, and lowers the SMPU crystallinity. The suitable TiO 2 content can increase the absorptivity to UV light and enhance the reflectivity to visible light of TiO 2 /SMPU nanocomposites, lowering its photo-aging properties and prolonging its service life. Also, TiO 2 /SMPU shows a higher scattering intensity and a faster decreasing trend than SMPU due to the larger electron density difference between TiO 2 and SMPU. The microphase separation and ordered structures in SMPU are decreased due to added TiO 2 nanoparticles. There are electron density fluctuations at the interfaces between hard and soft phases in SMPU, and between SMPU and TiO 2 nanoparticles. Finally, the prpared TiO 2 /SMPU nanocomposites have better shape memory effects and tensile properties when TiO 2 content of 3% is proposed to synthesize TiO 2 /SMPU nanocomposites for practical engineering applications.

To better understand the shape memory behaviors of synthesized shape memory polyurethane (SMPU) sealant with a tailored transition temperature (Tt) for concrete pavement joints, the thermal and dynamic mechanical properties of SMPU were first characterized to determine the shape memory switching temperature of SMPU. Then the microstructural and mechanical property evolutions of SMPU in the original, programmed, and recovered states during a five‐step thermodynamic cycle were discussed, respectively. The results indicate that the tailored Tt of prepared SMPU can be used as the shape memory switching temperature to match its working temperature. Further, the programming causes the phase separation in SMPU, leading to an obvious anisotropy. The SMPU has satisfactory shape memory performance. The orientation of molecular chains in soft segments is confirmed along the stretching direction. The oriented molecular chains can restore to the naturally curled state during the free recovery. Finally, the programming improves the mechanical properties of SMPU. The recovered SMPU shows a slight decrease in mechanical properties because of the partially impaired crystal structures and broken molecular segments during the programming and recovery. It is concluded that the synthesized SMPU with the specially tailored Tt is suitable to use as a sealant of concrete pavement joints. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45703.

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To evaluate the effects of epoxy resin (EP) on different properties of shape memory polyurethane (SMPU) when used as a sealant with a tailored thermal transition temperature (Tt) for concrete pavement joints, the thermal and dynamic mechanical performances were discussed to determine the shape memory switching temperature of EP-modified SMPU, and then the compatibility between EP and SMPU, microscopic morphology, shape memory effect, and tensile property were also characterized. The results indicate that the tailored Tt of EP-modified SMPU can be used as the shape memory switching temperature to match its working temperature. EP and SMPU show considerable compatibility. EP inhibits the crystallization of soft phase content and increases the hard phase content. Both hydroxyl and epoxy groups participate in chemical reactions. The ring-opening reactions occur between fractional benzenes and SMPU. EP was successfully grafted onto the main chains of SMPU. Additionally, the peak load, tensile strength, and elongation at break of SMPU are first increased and then decreased when the EP content increase. An EP content of 10 % improves the tensile properties of SMPU, but excessive EP content leads to a decrease in the tensile strength and elongation at break. Finally, it is found that a small amount of EP has little influence on the shape memory properties of SMPU, but EP can improve the tensile properties of SMPU. EP-modified SMPU shows excellent shape memory effects. The prepared EP-modified SMPU with the specially tailored Tt can meet the requirements of practical engineering when used as a sealant for concrete pavement joints.