Tuning the Properties of Shape-Memory Polyurethanes via the Nature of the Polyester Switching Segment

Shape-memory polymers that contain semicrystalline domains with a melting temperature (T_m) above and a crystallization temperature (T_c) below physiological temperature as fixing elements are useful to create medical devices or implants that can be custom-shaped inside or around the body. With the goal to expand the palette of materials that exhibit such properties, a series of segmented polyurethanes (PUs) containing different crystallizable polyester segments is investigated. The nature of the polyester, its molecular weight, and the ratio of hard to soft segments are systematically varied and the effect on the mechanical, thermal, and shape-memory properties of the various PUs is studied. Poly(1,12-dodecylene dodecanoate), poly(1,6-hexylene dodecanoate), and poly(ethylene sebacate) (PES) are selected as crystallizable polyester segments. The PES-based PUs display T_c values of 25–35 °C and a T_m of 60–63 °C, and allow good shape fixing at 37 °C.