Effects of soft segment molecular weight on the properties of recyclable polyurethanes with low-temperature multiple shape memory

Thermoplastic polyurethane (TPU) with shape memory characteristics exhibits excellent comprehensive performance and structural design flexibility, wherein the composition and structure of the soft segment play a crucial role. We synthesized four linear-structured polyurethanes (PUs) using 4,4′-methylene diphenyl diisocyanate (MDI), polytetramethylene ether glycol (PTMG), and 1,4-butanediol (BDO) in identical molar ratios and systematically investigated the impact of soft segment molecular weight on hydrogen bonding, thermal properties, microphase separation, and mechanical performance of TPU. The results show that an increase in soft segment molecular weight leads to a reduction in hydrogen bonding, microphase separation, and modulus, while the tensile strength initially increases and then decreases. PU650 exhibits the highest hydrogen bonding index of 5.17 and the maximum microphase separation. Additionally, all TPU materials exhibit low-temperature multiple shape memory behavior and excellent recyclability. This work provides valuable insights into the structural design and performance optimization of recyclable PU materials.