Preparation And Properties Of Vitrimer Based On Hydroxy Ester

Thermosetting materials are widely used in human life.However,due to the limitation of crosslinking network,it is difficult for materials to be recycled once formed.Therefore,it brings convenience to human beings and damages the environment on which human beings live.In 2011,Leibler et al.proposed the concept of "vitrimer",which made the traditional thermosetting materials enter a new era.Since then,vitrimer has become the research hotspot of many chemists and materials scientists at home and abroad.β-hydroxyl ester is a kind of stable dynamic covalent bond.The transesterification reaction can be carried out only under a certain temperature and catalyst,and the density of the crosslinking network remains unchanged before and after the reaction.Therefore,vitrimer based on transesterification reaction is one of the most widely studied reversible covalent cross-linked polymers in recent years.However,there are still some challenges when preparing vitrimer based on transesterification reaction.For different challenges,we have proposed corresponding solutions.Specific research contents are as follows:The acrylate vitrimer based on transesterification reaction has low strength,long curing time and high energy consumption.To this end,this topic with glycidyl methacrylate and suberic acid as raw materials,prepared the acrylate prepolymer GS containing β-hydroxyl ester.The reaction process was monitored by FTIR and 1H NMR Because the methyl methacrylate contains double bonds,the β-hydroxyl ester generated by the first step reaction is introduced into the photocuring system,which greatly reduces the curing time and energy consumption.Then,GS copolymerized with acrylamide and tetrahydrofuran acrylate with different contents in the presence of photoinitiator TPO,and hydrogen bonds were introduced into the cross-linking network.The results show that with the increase of acrylamide content from 0 to 20 wt%,the tensile strength of acrylate vitrimer increases from 9.1 MPa to 40.1 MPa,and the Young’s modulus and fracture energy of acrylate vitrimer also increase significantly.Through cyclic tensile test,the energy dissipation mechanism of material mechanical property enhancement was investigated,that is,hydrogen bond breaks before covalent bond.More inportantly,hysrogen bone dissociation occurs at 180℃,which soes not affect the network topological rearrangement of the acrylate vitrimer.In addition,acrylate vitrimer can be reprocessed at 180℃ and 1000 psi by β-hydroxyl ester exchange,and can be used in SLA 3D printing.The processed samples can also be intersoluble with ethylene glycol to achieve multiple chemical cycles.For most vitrimers based on transesterification,the materials used to construct them are generally limited to epoxies and carboxylic acids or anhydrides.In addition,the dynamic covalent bond of β-hydroxyl ester is often used to regulate the properties of materials,which has some limitations such as accidental failure.Therefore,aliphatic and aromatic epoxy resins with ester groups were synthesized in this project.At this time,vitrimer containing β-hydroxyl ester can be prepared by using either carboxylic acid or anhydride or amine curing agent widely used in the market.At the same time,an aromatic amine curing agent with disulfide bond was introduced into the crosslinking system,and a dual dynamic epoxy vitrimer with β-hydroxyl ester and disulfide bond was prepared.The influence of the content of hard segment and soft segment on the properties of the material in the crosslinking network was investigated.The results show that with the decrease of the content of aliphatic epoxy resin and the increase of the specific gravity of aromatic epoxy resin,the tensile strength of the material increases from 0.77 MPa to 4.97 MPa gradually,and the glass transition temperature,modulus and solvent resistance also increase in turn.The effects of single dynamic covalent bond and dual dynamic covalent bond on the self-healing and reprocessing properties of materials were compared.The results show that the synergistic action of β-hydroxyl ester and disulfide bond allows the dual dynamic epoxy vitrimer to be hot-pressed at 180℃ and 800 psi for only 5 min,and the maximum repair efficiency is close to 100%.However,under the same experimental conditions,the single dynamic epoxy vitrimer containing β-hydroxyl ester needed 2 h to complete the remodeling,and the repair efficiency was only about 25%.In addition to addressing the above challenges,we have synthesized silver nanoparticles/epoxy vitrimer complexes in site,which combine silver nanoparticles with excellent performance with vitrimer based on transesterification reaction and broaden the application range of them.The coordination between silver acetate and D230 was characterized by FTIR and Raman,and the existence of silver nanoparticles was confirmed by TEM and XRD.The introduction of silver nanoparticles improves the thermal stability and mechanical properties of vitrimer based on transesterification reaction,and reduces the temperature of curing reaction.