# Shape Memory Polyurethane and its Composites for Various Applications
## 2 Shape Memory Polyurethane in Different Applications
### Self-Healing
Figure 10: Demonstration for self-welding ability of welded polyurethane vitrimers with 3 wt% catalyst dibutyltin dilaurate (PUV-3) sample: Stress-strain curve (**a**) at different time at 150 \({}^{\circ}\)C and (**b**) at different temperatures for 5 min welding, (**c**) lap-shear test, (**d**) modes of fracture of different samples [60]. In another similar work, [PERSON] et al. [70] reported the self-healing and shape memory properties of polytetramethylene ether glycol (PTMEG) based polyurethane containing diselenide bonds induced by NIR radiation. In order to enhance the photo-thermal activity resulted from NIR radiation, they covalently incorporated the functionalized graphene oxide into polyurethane. They found that the presence of diselenide bonds greatly enhanced the self-healing capability (\(\sim\)90%) of the prepared composites. They concluded that the synergistic photo-thermal response and dynamic exchangeable diselenide bond contributed towards the curing of damaged sites resulting in complete healing. Similarly, [PERSON] and colleague [69] have used the same PTMEG based polyurethane embedded with dynamic covalent bonds using disulfide bond in its backbone chain which are responsible for its conditional self-healing ability. Increasing the content of disulfide bond (12%) showed efficient self-healing efficiency (94%). After the damage, the prepared material was healed due to the disulfide exchange in the matrix at elevated temperature (55 \({}^{\circ}\)C) for 30 min. In a work reported by [PERSON] et al. [65], utilization of the dynamic reversible covalent bonding for repeated intrinsic self-healing of wider cracks in PCL based polyurethane has been presented. They prepared the composite of polyurethane, styrene-butadiene-styrene block copolymer (SBS), and MWCNTs. They modified the crosslinked elastomeric SBS block copolymer sphere via an addition of alkoxyamine into the backbone and used as internal stress generator (Figure 12). Incorporation of alkoxyamine moieties, which works as intermolecular links, gives an additional feature of synchronous bond fission/radical  
Figure 11: **(a)** Illustration of the healing process of polyurethane composite with 50% thermoplastic polyurethane, 50% polycaprolactone and 3% MWCNT (U1C1-3) using near infrared (NIR) irradiation (808 nm, 0.5 W, 15 cm), (**b**) optical images of scratched and healed surfaces, stress-strain curves for U1C1-3 samples (**c**) with different irradiation times and (**d**) with healing cycles [71]. recombination based on dynamically reversible C-ON bond to SBS. Heating to its homolysis temperature, the temperature at which the chemical bond dissociation of molecules occur and the involved electrons distribute between the formed fragments, triggers synchronous covalent bond fission and radical recombination among alkoxyamine moieties is triggered which help repeatedly self-healing without affecting the mechanical and shape memory properties [74]. They also incorporated MWCNTs to improve the electric conductivity of insulating polyurethane which helped to stimulate shape memory by Joule heating. In the exploration of materials with self-healing ability, [PERSON] and coworkers [68] developed polyurethane based on cyclic polycaprolactone and incorporated dynamic covalent bond into the polymer system by the addition of furan and maleimide moiety (Diels-Alder adducts). They found cyclic topology of polycaprolactone affected the shape memory and self-healing properties of the developed crosslinked polyurethane. They established using Fourier-transform infrared spectroscopy technique that furan and maleimide were formed into the polymeric system upon thermal heating at 130 \({}^{\circ}\)C for 5 min due to the retro Diels-Alder reaction which disappeared after cooling to 60 \({}^{\circ}\)C for 48 hours. Overall, the developed material showed 70% self-healing ability as per the mechanical pull test. Self-healing can also be triggered using moisture or water hydration and dehydration at relatively lower temperatures.