Stiff Yet Elastic Thermoplastic Polyurethanes Based on Nanoconfined Stereocomplexation in PLA Interphases

Stiffness and elasticity are generally considered mutually exclusive properties in thermoplastic polyurethanes (TPUs), as embodied by the counterbalance between hard and soft content. In this work, we report the design strategy of a family of stereocomplexed poly(lactide) (scPLA)-containing TPUs, where short strands of the two PLA stereoisomers (PLLA and PDLA) are covalently introduced into the chain architecture in order to achieve elastomers with simultaneously high moduli, toughness, elasticity, and biomass incorporation. Through fine-tuning of segment lengths and ratios, we identified an optimal composition in which the resulting TPU exhibits an extraordinary Young’s modulus of ∼100 MPa and a heat resistance of 150 °C, while only marginally compromising toughness and elasticity. X-ray diffraction (XRD) and atomic force microscopy (AFM) confirm that scPLA forms exclusively in the stereocomplexed TPU, giving rise to a unique bicontinuous microphase-separated structure that is heavily loaded with scPLA nanofibrils. These “intrinsic fillers” are not only key to superior mechanical and thermal characteristics in our materials design but also highlight the potential of scPLA as an essential building block toward the ultimate goal of developing fully biobased, high-performance TPU products.