High-strain shape memory polymer networks crosslinked by SiO2

We addressed a novel high-strain shape memory polymer network constructed from SiO2 microspheres core functionalized with polycaprolactone arms. Using abundant surface hydroxyl of silica, epsilon-caprolactone was initiated and uniform SiO2@PCL macroparticles were formed; after cross-linking of SiO2@PCL by MDI, a high-strain shape memory polymer network of SiO2-SMP was obtained. Compared to traditional SMP having similar composition, the SiO2-SMP exhibits excellent mechanical strength and good shape memory properties due to the introduction of SiO2 as a cross-linking point. The elastic moduli (E) and tensile strength (sigma(m)) of the SiO2-SMP were improved to 500 MPa and 90 MPa, respectively, at room temperature. It could be attributed to the enhancement of the combining force among polymer chains caused by the crosslinking networks, and the rigidity of the polymer owing to the addition of SiO2 as filler. High shape fixing ratios (similar to 100%) and recovery ratios (more than 95%) were also exhibited for SiO2-SMP from the second circle. The comparatively low recovery ratios were exhibited in the first circle; the obvious evidence of the existence of the irreversible bond breakage is attributed to it. Furthermore, the mechanical and shape memory properties could be adjusted by changing the size of silica microspheres and the molecular weight of the PCL.