Synthesis of chemically-crosslinked multi-arm star-shaped polyurethane with triple-shape memory effect

In this study, chemically-crosslinked multi-arm star-shaped polyurethanes (SPUs) were prepared using three, four, and six-arm polycaprolactone, hexamethylene diisocyanate, and 1, 4-butanediol. The hydrogen bonding indices of soft and hard segments were calculated using Fourier transform infrared spectra. The results indicated that the phase separation among hard and soft segments increased with the increment of PCL arm numbers. Moreover, the results of X-ray diffraction and differential scanning calorimetry showed that the crystallization ability of the three and four-arm SPUs were lower than that for six-arm SPU (6SPU), which is due to their higher crosslinking densities. In addition, the results of the mechanical studies showed that the crosslinking density and degree of crystallinity are the main effective parameters controlling the mechanical properties, by which 6SPU showed higher Young's modulus and lower elongation at break compared to other SPUs. Cyclic shape memory studies showed that 6SPU could fix approximately all the temporary shapes during three cycles and recover 100% of its original shape. Moreover, 6SPU could show triple-shape memory effect (TSME) by which it could fix two different temporary shapes. These results show that 6SPU has a high potential for practical applications due to its good mechanical properties, shape memory fatigue resistance, and TSME.

Evaluation performance of azobenzene liquid-crystal shape memory polyurethane with photo-thermo-synergy response

This paper aimed to investigate the photo-response performance of a polymeric material using a series of azobenzene liquid-crystal shape memory polyurethane (DB-SMPn) with azobenzene-4,4'-dicarboxylic acid (ADA), N, N-bis (2-hydroxyethyl) isonicotinamine...

Shape-Memory and Self-Healing Polymers Based on Dynamic Covalent Bonds and Dynamic Noncovalent Interactions: Synthesis, Mechanism, and Application

Shape-memory and self-healing polymers have been a hotspot of research in the field of smart polymers in the past decade. Under external stimulation, shape-memory and self-healing polymers can complete programed shape transformation, and they can spontaneously repair damage, thereby extending the life of the materials. In this review, we focus on the progress in polymers with shape-memory and self-healing properties in the past decade. The physical or chemical changes in the materials during the occurrence of shape memory as well as self-healing were analyzed based on the polymer molecular structure. We classified the polymers and discussed the preparation methods for shape-memory and self-healing polymers based on the dynamic interactions which can make the polymers exhibit self-healing properties including dynamic covalent bonds (DA reaction, disulfide exchange reaction, imine exchange reaction, alkoxyamine exchange reaction, and boronic acid ester exchange reaction) and dynamic noncovalent interactions (crystallization, hydrogen bonding, ionic interaction, metal coordination interaction, host-guest interactions, and hydrophobic interactions) and their corresponding triggering conditions. In addition, we discussed the advantages and the mechanism that the shape-memory property promotes self-healing in polymers, as well as the future trends in shape-memory and self-healing polymers.