Strategy for regulating one-way and two-way shape memory effects in crystalline thermoplastic polyurethane

Shape memory polymers (SMPs) are one of the most typical intelligent materials. However, the precise regulation of the shape memory effect (SME) remains a critical challenge in the field. This study introduces a simple strategy for regulating the SME, employing crystalline thermoplastic polyurethane (CTPU) as the raw material and utilizing isophorone diisocyanate (IPDI) trimer to regulate both one-way SME (1W-SME) and two-way SME (2W-SME). Results showed that incorporation of IPDI-trimer induced a cross-linked network within CTPU. The tensile strength at break reached a maximum of 27.4 MPa, and the elongation at break remained relatively high (2484%) when the IPDI-trimer content was below 10wt%. The resulting cross-linked CTPU exhibited exceptional one-way shape memory performance, achieving a 99.9% recovery rate and 96.4% fixation rate. Notably, switchable 2W-SME emerged when IPDI-trimer concentrations exceeded 11wt%. This dual SME functionality, coupled with a 54.3% actuation magnitude, signified a significant advancement in SMPs capabilities. Systematic analysis reveals that shape memory activation originates from the synergistic effects of oriented crystalline domain melting and energy release within the cross-linked network under thermal stimuli. The precise control of 1W-SME and 2W-SME demonstrated in this study fundamentally arises from regulated crystallinity and cross-linking degree of CTPU. Owing to these enhanced integrated properties, these materials show great promise for diverse applications, particularly in smart sensors and intelligent robotics.