Control of PLA Stereoisomers-Based Polyurethane Elastomers as Highly Efficient Shape Memory Materials

Poly­(lactic acid) (PLA) has received increasing attention in the development of shape memory polymers (SMPs) due to its excellent physical properties and good biocompatibility. However, the intrinsically increased crystallinity of PLA at higher deformation ratios still remains a significant challenge, which remarkably restricts the chain mobility and reduces shape recovery efficiency. Being different from other types of biodegradable polymers, the diverse isomeric forms of PLA have provided great opportunities for modulation of PLA toward a favorable property by incorporating different PLA stereoisomers in one macromolecular architecture. In this paper, we report a completely amorphous PLA poly­(ester urethane) elastomer that exhibits excellent shape fixity (>99%) and shape recovery (>99%) in a time frame of seconds. By means of adjusting the stereoisomeric ratios and control over architecture, the resultant poly­(PLLA/PDLLA urethane)­s (PLDU) elastomers show a single glass transition temperature (T_g), as the only thermal event, in the range of 38–46 °C in a predictable manner. The elastic moduli of PLDU elastomers display a 100-fold loss during the sharp transition from a glassy to a rubbery state with temperature alternation across their corresponding T_g, indicating a successful manipulation of the thermo-mechanical properties by temperature as required in thermally induced SMPs. In addition, all samples display a typical elastomeric behavior with elongation at break (ε_b) greater than 400%. The effect of the stereoisomer content on the tensile modulus and elastic mechanical behavior were also systematically investigated. Together with the prominent degradation property, the new PLDU elastomers developed in this study show great potential for biomedical applications as shape memory implants.