One-way and two-way shape memory behaviour of semi-crystalline networks based on sol-gel cross-linked poly(epsilon-caprolactone)

In this work we have explored the shape memory capabilities of a novel type of covalently cross-linked semi-crystalline polymers, prepared by exploiting the mild sol gel chemistry, starting from alkoxysilane-terminated poly(epsilon-caprolactone) (PCL), and using silica-based domains as cross-link points. By adopting PCL precursors with different molecular weights, semi-crystalline networks with well defined cross-link densities and with different crystallization and melting temperatures were obtained. Beside a satisfying one-way shape memory behaviour, the materials have displayed a significant two-way shape memory response, undergoing a reversible elongation-contraction process between two distinguished strain levels when subjected to a constant load and cyclically heated/cooled on a temperature region spanning from below the crystallization temperature to above the melting temperature. The applied load and the cross-link density are revealed as key-parameters to obtain tailored actuations. Concurrent wide-angle X-ray diffraction (WAXD) and DSC analyses allowed to ascribe the effect to a structural evolution process occurring during melting and crystallization.