Synthesis And Self-healing Properties Of Crosslinked Polyurethane Based On Acylhydrazone Bonds And Disulfide Bonds

Micro-cracking will inevitably produce within matrix during the production and application of polymeric materials.Micro-cracks will develop into cracks and eventually lead to the destruction of polymeric materials.Besides,Micro-cracking is also the direct cause of material property deteriorates continuously.This is a very valuable method for polymeric structural materials to incorporate the self-healing property into polymeric materials since it effectively expands the lifetime use of the product and has desirable economic and human safety attributes.Self-healing polymeric materials are currently the subject of active research.A particularly useful approach to generate self-healable polymers has been the introduction of dynamic covalent bonds(such as Diels–Alder reaction,acylhydrazone bonds,imine,disulfide bonds,reversible C–ON bonds,trithioesters,diarylbibenzofuranone,phenylboronic acid ester bonds)into the polymeric materials.In addition to normal properties of conventional polymers such as strength and stability,these dynamic covalent polymers have shown the ability to exchange components between different polymer chains by the exchange reaction of the dynamic covalent bonds.In the majority of cases,an appropriate external stimulus(such as pH,light,temperature and catalysts)is required,in order to promote the exchange reaction of the dynamic covalent bonds.This feature enables these dynamic covalent polymers to repair their damage.Acylhydrazone and disulfide bonds are widely used in the preparation of self-healing polymeric materials due to they are simple to prepare,easy to repair at room temperature,not interfere with each other in a same system,commonly used in the preparation of multi-responsive self-healing polymeric materials.In this paper,the dihydric alcohol containing acylhydrazone bonds,the dihydric alcohol containing disulfide bonds and the dihydric alcohol containing acylhydrazone and disulfide bonds were first synthesized and then introduced into polyurethane.Besides,their self-healing properties were also studied.The main contents and results of this paper are as follows:1.Synthesis of polyurethane gel based on acylhydrazone bonds: Dihydric alcohol containing acylhydrazone bonds was synthesized in the acid environment by using p-hydroxybenzaldehyde and adipicdihydrazide as reaction materials.Besides,polyurethane gel(PA-H/DMSO gel)based on acylhydrazone bonds was prepared by the reaction of Dimethyl sulfoxide solution of PA and HDI trimer.The rheological properties of PA-H/DMSO gel demonstrated that this gel is a typical chemical gel and has a good rubber elasticity.The polyurethane gel exhibits significant fluid properties and can be decomposed through reverse reaction under heating and acid or aniline conditions.The self-healing of polyurethane gel can be achieved through heating under acid or aniline conditions;the self-healing efficiency of polyurethane gel under acid conditions is much larger than the self-healing efficiency under aniline conditions;the self-healing efficiency of polyurethane gel after 6h of healing time under 80? and acid conditions can be achieved 89.47%.2.Synthesis of self-healing polyurethane based on disulfide bonds: Dihydric alcohol containing disulfide bonds(2,2'-dithiobis-ethanol)was synthesized by the oxidation of DMSO.The self-healing polyurethane based on disulfide bonds was prepared by the reaction of 2,2'-dithiobis-ethanol and HDI trimer.The self-healing of this polyurethane material can be achieved by heating at 130?.The self-healing efficiency of the polyurethane material after 6h of healing time can be achieved 52%.3.Synthesis of room-temperature self-healing polyurethane elastomers: two kinds of polyurethane elastomers were synthesized.One containing acylhydrazone bonds is named TPIA.The other containing both acylhydrazone and disulfide bonds is named TPID.Self-repairable ability and reprocessability of these two elastomers were studied.The results show that the polyurethane elastomer TPIA can not repair its damage under neutral conditions.The self-healing of this polyurethane elastomer can be achieved under acidic conditions due to the cleavage and the exchange reaction of the acylhydrazone bonds was promoted under acidic conditions.After self-healing for 24 h,the strength and the elongation value at break recovered to 32% and 55% of the originality,respectively.The polyurethane elastomer TPID can automatically repair damage to it under visible light at room temperature.After 24 h of self-healing time,75% of the original strength and 100% of the original elongation values at break were obtained.These two polyurethane elastomers can be reprocessed in their cured state by just applying temperature and pressure.