Synthesis And Performance Study Of Photo-Responsive Coumarin-based Self-healing Materials Based On Synergistic Action Of Disulfide And Azo Compounds

The self-healing material by light stimulus has become a popular self-healing material due to its advantages of low cost,environmental protection,no damage to the material in the self-healing process and the ability of real-time and remote control to realize the local fixed-point healing of the material.Coumarin-based photo-responsive self-healing materials have good biocompatibility,photo-responsiveness and stability to heat and avoid the problem of isomerization.However,in the process of self-healing of coumarin-based photo-responsive self-healing materials,the photoreversible reaction efficiency is reduced because of the increase of the distance between coumarin double bonds,thereby weakening the self-healing ability of the materials.Therefore,a new strategy to improve the photoreversible reaction and self-healing efficiency of coumarin-based self-healing materials without an excessive impact on polymer properties is still a current research hotspot.Disulfide compounds can generate sulfur free radicals under the stimulation of ultraviolet and realize the self-healing of materials through the exchange reaction between them.Meanwhile,the exchange reaction of disulfide bonds can drive the polymer chain to move.Under the irradiation of ultraviolet,azo compounds can occur trans-cis isomerization to guide the movement of side chains of the polymers,thereby stimulating the movement of the main chain of the polymers and reducing the glass transition temperature.Based on this,we propose the introduction of disulfide and azo compounds into coumarin-based self-healing materials,respectively,to improve the chain mobility of the polymer during self-healing,reduce the glass transition temperature of the system and make the coumarin units on the polymer chain get close to each other easily,thereby enhancing the self-healing efficiency of the materials.The effects of the introduction of disulfide and azo compounds,the proportion and content of photoreactive monomers,the structures of coumarin-based monomers,and the structures,proportion and contents of hard and soft monomers on the photopolymerization behaviour,thermal and mechanical properties as well as self-healing properties of coumarin-based self-healing materials were systematically studied.The internal relationship between the structure and performance of self-healing materials was obtained.This research can provide theoretical basis for the design of self-healing materials.The main research contents and conclusions of this paper are as follows:1.Photo-responsive monomer containing disulfide bond(BAEDS)and monomer containing coumarin group(MAHCM)were prepared using thiodipropionic acid,hydroxy ethyl acrylate,hydroxymethyl coumarin and 6-bromine cyclohexanol as raw materials,then BAEDS and MAHCM were mixed with other monomers in different ratio and a series of photo-responsive coumarin self-healing materials based on the synergistic action of disulfide was prepared by photopolymerization.The influences of the kind of photoinitiator,disulfide monomer content and adding ratio of soft monomer to hard monomer on the photopolymerization behaviour,thermal and mechanical properties as well as self-healing properties of self-healing materials were explored.The results show that 2,4,6-trimethylbenzoyl-diphenylphosphine oxide(TPO)as the photoinitiator could well induce photopolymerization of the coumarin-based self-healing system based on synergistic action of disulfide,and BAEDS itself had no initiating ability.The content of hard and soft monomers had no effect on the photopolymerization performance of the system.The initial degradation temperature(T10%)of the self-healing materials was higher than 280?.As the content of soft monomer EOEOEA increased and the content of hard monomer IBOA decreased,the flexibility of the polymer increased and its glass transition temperature decreased.When the content of IBOA increased and the content of EOEOEA decreased,the tensile strength of the polymer material increased,and the elongation at break and the self-healing efficiency decreased.The addition of BAEDS into the system could improve the self-healing efficiency of the material.The self-healing efficiency of tensile strength and elongation at break of SE04-IB6 reached about 85%and 87%,respectively.2.Three coumarin monomers(ATMCM,AHMCM and ANMCM)with different 7-position substituents were designed and synthesized.The effect of different 7-position substituents on the photopolymerization and self-healing properties of self-healing materials was investigated.The results show that the coumarin-based monomers with different 7-position substituents had no significant effect on the photopolymerization performance of the system when the photoinitiator TPO was added with a certain amount.With the increase of 7-position substituent chain length of the coumarin-based monomer,the tensile strength of the polymer decreased and the elongation at break increased.When the mass fraction of the monomer in the system was constant,the self-healing efficiency of the polymer increased firstly and then decreased with the increase of the distance between the coumarin group and the main chain.The SAH-5 with the distance of nine atoms between the coumarin group and the main chain had the highest self-healing efficiency of tensile strength and elongation at break.3.Two photo-responsive monomers,coumarin-based monomer MAHCM and azophenyl monomer MAH-Azo,were prepared by using 7-hydroxycoumarin,4-butylaniline,phenol,6-bromohexanol and methyl acryloyl chloride.Then MAHCM and MAH-Azo were mixed with other monomers in different ratio and a series of photo-responsive coumarin-based self-healing materials based on the synergistic action of azobenzene was prepared by thermal polymerization.The effects of the contents of photoreactive monomers,and the structures and contents of acrylate monomers on the mechanical properties and thermal stability of photo-responsive self-healing materials were investigated.The results show that all the self-healing materials had excellent heat resistance,and the initial decomposition temperature(T5%)was higher than 270?.As the contents of photoresponse monomers decreased and the content of acrylate monomers increased,the glass transition temperature of the polymer decreased,and the longer the chain length of acrylate monomers,the lower the glass transition temperature.The preliminary study on the self-healing ability of CM10-BM9 polymer shows that the polymer exhibited a good self-healing ability under only light stimulation without heating and the introduction of azobenzene structure could promote the self-healing behavior of the polymer.