Study On The Structural Design And Self-healing Properties Of Flexible Polyurethane

Endowing the material with self-healing ability is helpful to hand out the mechanical damage of flexible devices,which caused by repeated bending,stretching and twisting.However,the polymers with intrinsic self-healing ability are facing the problem of incompatibility between mechanical properties and self-healing performance.Furthermore,most self-healing polymers require additional intervention to ensure complete contact of the damaged interface during the self-healing progress.In order to solve the problems,the main goal of this paper is to synthesize high-toughness selfhealing polyurethane that can spontaneously close wounds.At first,the study focused on the aliphatic disulfide bonds and intermolecular hydrogen bonds based on the carboxylic acid,and investigated the effects of dynamic bond contents and soft segments on the structure and properties of polyurethane.Then,the self-healing polyurethane based on polycaprolactone(PCL)was synthesized,and the effect of segment structures on the shape recovery ability as well as self-healing behavior of polycaprolactone-based polyurethane was clarified.Later,the aliphatic and aromatic hard segments were simultaneously introduced to synthesize the polyurethane with high self-healing efficiency and superior toughness.Finally,the strain-induced stretchable conductors with high thermal conductivity and electrical conductivity were prepared and used in the field of strain sensing.This research is mainly divided into the following four aspects:(1)A series of polyurethanes containing aliphatic dynamic disulfide bonds and carboxylic acid functional groups were synthesized.The polyurethane exhibits excellent self-healing properties due to the reversible exchange reaction of S-S bonds.Increasing the temperature is benefit to promote the dissociation of intermolecular hydrogen bonds and inprove the self-healing efficiency to 93.7%.(2)A series of polyurethanes with different hard segments were synthesized and analyzed.The effects of hard segment types and contents on the crystallization of PCL segments,the polyurethane microphase morphology and properties were clarified.The aromatic hard segments containing disulfide bonds can significantly dissipate energy under large strains and enhance polyurethanes.The aliphatic hard segment participated in the crystallization of the PCL soft segment and enhance the stability of the phase interface.The PCL-rich region is able to store conformational entropy and exhibits shape memory-assisted self-healing behavior at the temperature above the melting point of PCL.(3)Considering the respective advantages of the aliphatic hard segment and the aromatic hard segment in adjusting the structure and properties of polyurethane,two different hard segments are introduced at the same time.The soft phase with low crystallinity and the loosely stacked hard segments make the mechanical properties and self-healing properties of the polymer increased simultaneously.(4)A multi-layered composite material was obtained by means of strain-induced BN orientation,dopamine surface modification,and heat-induced shape recovery,by virtue of the excellent tensile properties and high shape recovery ability of high-toughness self-healing polyurethane,which is used as a strain sensor to detect the movement of human joint.In conclusion,this paper focuses on investigating the effect of segment structure on the heterophasic morphology and final properties of polymers,and makes a useful study in extending the functionality of self-healing polyurethanes.The soft and hard phases synergistically optimizes the mechanical and self-healing properties of the polyurethane.The crystallized soft phase stores conformational entropy effectively,which is benefit to closing the wound.And the dynamic bonds in the hard phase made contribution to the healing process around interface.In addition,the orientation and recrystallization of soft segments at large strains also contributed to the improvement in strength of polyurethane.On the other hand,the dynamic bonds in hard segments dissipate strain energy by dissociation and rearrangement,which stabilized the newly generated crystalline regions.Thus,the polyurethane can withstand greater external forces.