Preparation And Properties Of Double-Crosslinked Self-Healing Polyurethane Materials Based On Quadruple Hydrogen Bonds

By mimicking the self-healing behavior of organisms in nature,researchers have developed a series of functional self-healing materials.The self-healing materials,as one of the promising smart materials,have the ability of repairing the damage.The design of self-healing materials is mainly started from two aspects: one is to doping microcontainers containing repair agents inside the polymer,and the other is to connect dynamic bonds in the polymer system.For the latter,UPy(2-ureido-4[1H]-pyrimidinone)system based on quadruple-hydrogen bonds has been widely applied to the field of self-healing.Polyurethane(PU)is a kind of versatile material with excellent stability,resilience and mechanical properties.However,in the practice applications,polyurethane materials are easy to appear inside micro-cracks.These cracks are hard to detect and reduce the mechanical properties and service life of the material.To solve this problem,this paper is focus on the preparation of room temperature self-healing polyurethane.The UPy system was prepared as the chain extender and was introduced into the polyurethane system in the form of side chain.The double cross-linking self-healing polyurethane elastomers with physical cross-linking and different chemical cross-linking were prepared,respectively.Therefore,the research content of this paper is as follows:Firstly,UPy-NCO was synthesized by 6-Methylisocytosine and hmethylene diisocyanate(HDI).Then UPy chain extender was synthesized by UPy-NCO and amino-methyl-propanediol(AMPD).The synthesis process was optimized and the best mass fraction of the solvent was confirmed.The proportion of UPy chain extender,1,4 butanediol(BDO)and crosslinking agent(triethanolamine)was controllable to prepare a series of double crosslinking polyurethane elastomers(PU-UPy).By adjusting the degree of physical crosslinking,self-healing polyurethane elastomers with UPy chain extender proportions of0%、 25%、 50% and 75% were prepared,respectively.The results showed that with the increase of UPy side chain content,the thermal stability of the material has little change,the glass transition temperature increases,and the chain segment mobility decreases slightly.The hardness and tensile strength were greatly improved as the inceasing of UPy content.When the content of UPy was the highest,the hardness and the tensile strength were greater than that of pure polyurethane without solvent.Elastic recovery was enhanced and the recovery was faster and faster as the increase of UPy content based on the results of cyclic performance tests.Secondly,by controlling the degree of chemical crosslinking,self-healing polyurethane elastomers with crosslinking agent ratio of 0% 、 10% 、 20% and 30% were prepared,respectively.The experimental results showed that with the increase of the proportion of crosslinking agent,the thermal stability of the material increased,the glass transition temperature increased,and the movement of chain segment became difficult.Though the peak of loss factor decreased as the increasing of the UPy content,the damping performance at room temperature still kept excellent.The hardness and the tensile strength were greatly improved as the inceasing of UPy content.Elastic recovery became stronger and the cyclic recovery became weaker as the inceasing of UPy content.In addition,it was found that when the proportion of crosslinker was between 10% and 20%,the hard segment as crosslinker might be concentrated and dispersed in the soft segment.Finally,self-healing experiments for two kinds of crosslinked proportional polyurethane elastomers were carried out.The self-healing temperature and the mechanical properties of polyurethane elastomers after repairing were investigated,respectively.The experimental results showed that when the repair time was prolonged,the dissociation of hydrogen bond and the movement of chain segment had sufficient time to repair the damage,resulting that the repair efficiency went up.When the temperature was rised,the dissociation and recombination ability of hydrogen bond and the movement ability of chain segment were improved,resulting that the repair efficiency went up,too.With the increasing of UPy side chain content,the repair efficiency of PU70-10 decreased slightly at first and then improved.After repairing for 24 hours at 40 ℃,the self-repair efficiency of PU70-10 reached 73%.With the increasing of crosslinker content,the repair efficiency of PU50-30 decreased gradually and the self-repair efficiency of PU50-30 still reached 48% after repairing for 24 hours at 40 ℃.