| Summary: | In order to further understand the shape memory mechanism of a silicon dioxide/shape memory polyurethane (SiO<sub>2</sub>/SMPU) composite, the thermodynamic properties and shape memory behaviors of prepared SiO<sub>2</sub>/SMPU were characterized. Dynamic changes in the molecular orientation and interphase structures of SiO<sub>2</sub>/SMPU during a shape memory cycle were then discussed according to the small angle X-ray scattering theory, Guinier’s law, Porod approximation, and fractal dimension theorem. In this paper, a dynamic mechanical analyzer (DMA) helped to determine the glass transition start temperature (<i>T</i><sub>g</sub>) by taking the onset point of the sigmoidal change in the storage modulus, while transition temperature (<i>T</i><sub>trans</sub>) was defined by the peak of tan δ, then the test and the calculated results indicated that the <i>T</i><sub>g</sub> of SiO<sub>2</sub>/SMPU was 50.4 °C, and the <i>T</i><sub>trans</sub> of SiO<sub>2</sub>/SMPU was 72.18 °C. SiO<sub>2</sub>/SMPU showed good shape memory performance. The programmed SiO<sub>2</sub>/SMPU showed quite obvious microphase separation and molecular orientation. Large-size sheets and long-period structures were formed in the programmed SiO<sub>2</sub>/SMPU, which increases the electron density difference. Furthermore, some hard segments had been rearranged, and their gyration radii decreased. In addition, several defects formed at the interfaces of SiO<sub>2</sub>/SMPU, which caused the generation of space charges, thus leading to local electron density fluctuations. The blurred interphase structure and the intermediate layer formed in the programmed SiO<sub>2</sub>/SMPU and there was evident crystal damage and chemical bond breakage in the recovered SiO<sub>2</sub>/SMPU. Finally, the original and recovered SiO<sub>2</sub>/SMPU samples belong to the surface fractal system, but the programmed sample belongs to the mass fractal and reforms two-phase structures. This study provides an insight into the shape memory mechanism of the SiO<sub>2</sub>/SMPU composite.
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