Highly Improved Shape Memory Properties of a PCL-Based Polyurethane via Polylactide Stereocomplexation

In shape memory polymers (SMPs) composed of semicrystalline polymers, their crystallization-melting process and the overall entropic elasticity of the material determine their shape memory behavior. In this work, cross-linked polyurethanes with polycaprolactone (PCL), poly(l-lactic acid) (PLLA), and poly(d-lactic acid) (PDLA) segments were designed, in which four-armed PCL served as the chemical cross-linking and polylactic acid (PLA) crystals acted as physical cross-linking. By adjusting the molecular weight of the four-armed PCL and the type of PLA crystals [homocrystals (HC) and stereocomplex (SC) crystals], the overall cross-linking degree of the material was controlled, and the crystallization behavior, mechanical properties, and shape memory behavior of the material were studied. The results indicated that both physical and chemical cross-linking significantly affect the mechanical properties and shape memory properties of materials. Moreover, polyurethane-contained SC exhibited a higher shape recovery ratio (<i>R</i>_r) and fixation ratio (<i>R</i>_f) than polyurethane-contained HC because SC provided higher entropy elasticity and promoted PCL crystallization. This study provides a method for synergistically enhancing <i>R</i>_f and <i>R</i>_r of SMPs, offering insights into the design of related materials.