Thermoplastic shape-memory polyurethanes based on natural oils

A new family of segmented thermoplastic polyurethanes with thermally activated shape-memory properties was synthesized and characterized.Polyols derived from castor oil with different molecular weights but similar chemical structures and a corn-sugar-based chain extender (propanediol) were used as starting materials in order to maximize the content of carbon from renewable resources in the new materials.The composition was systematically varied to establish a structure-property map and identify compositions with desirable shape-memory properties.The thermal characterization of the new polyurethanes revealed a microphase separated structure, where both the soft (by convention the high molecular weight diol) and the hard phases were highly crystalline.Cyclic thermo-mechanical tensile tests showed that these polymers are excellent candidates for use as thermally activated shape-memory polymers, in which the crystalline soft segments promote high shape fixity values (close to 100%) and the hard segment crystallites ensure high shape recovery values (80-100%, depending on the hard segment content).The high proportion of components from renewable resources used in the polyurethane formulation leads to the synthesis of bio-based polyurethanes with shape-memory properties.