Effects of Hard Segment of Polyurethane with Disulfide Bonds on Shape Memory and Self-Healing Ability

Self-healing polyurethane with disulfide bonds was synthesized using polycarbonate diol as a soft segment, and methylene diphenyl diisocyanate and 2-hydroxyethyl disulfide as a hard segment. Well-developed phase separation as the hard segments increased was confirmed by Fourier transform infrared spectra. The X-ray diffraction data showed that the crystallinity of the polycarbonate with a semicrystalline structure decreased as the HS increased, which affected the thermal, mechanical, and thermomechanical properties of the PU block copolymer. As the hard segments increased, the yield point on the strain-stress curve disappeared, and the mechanical properties (elongation at break and breaking stress) and the shape recovery rate of SHPU improved. The increase in the physical crosslinking between the hard segments contributed to improving shape recovery and mechanical properties. In particular, self-healing polyurethane with 30, and 35 wt% hard segments showed excellent self-healing ability at 80 C, while the self-healing ability for self-healing polyurethane with 40 wt% hard segments was decreased. The increase of the hard segment restricted the movement of the soft segment, thus the self-healing ability of SHPU with 40 wt% HS was decreased. It could be concluded that self-healing polyurethane synthesized using semicrystalline PC diol has a significant effect on shape recovery and self-healing efficiency due to the crosslinks between the hard segments.