Preparation And Controllable Bonding Properties Of Self-healing Photo-cross Linking/photo-reversible 3d Network

Quartz devices have an important position in the optical systems such as 5G communications,space telescopes and medical instruments.Adhesives have a wide range of applications in optical systems and are important materials for the assembly,fixation and sealing of quartz devices.Reversible adhesives play an important role in the disassembly and maintenance of quartz devices.Traditional thermoplastic adhesives,such as hot-melt adhesives and thermoplastic polyurethanes,usually experience stress relaxation due to the lack of a stable cross-linking structure.In the use of quartz devices,the problems of displacement and misalignment of devices often occur.Thermoreversible thermosetting adhesives,including DA bond epoxy adhesives,disulfide bond epoxy adhesives and transesterified epoxy adhesives,often require high temperature to break the reversible bond,which is extremely inconvenient for large devices,and heat may cause irreversible damage to some critical components.Therefore,light-induced reversible adhesive will become a new choice for quartz devices bonding.In this paper,coumarin and anthracene groups were introduced into the thiol-ene networks respectively.Based on the principles of click chemistry and cycloaddition,polymers with photoreversible properties were prepared,and the performance changes during their light response were investigated.The self-healing of the adhesives and the light-induced reversible bonding of the quartz devices were realized.The systems use only light during preparation,curing,bonding,and disassembly,with no need for heat or other stimuli.The problems of adhesive damage and difficult disassembly in the bonding process of the quartz device were solved.The main research contents and the results obtained are as follows.1.Coumarin-based thiol-ene networks were designed and synthesized,and their self-healing properties and bonding properties were explored.Using 7-hydroxycoumarin as a raw material,coumarin-based thiol-ene polymer networks with different network densities were obtained after cycloaddition reaction,allylation reaction and click chemical reaction.The thermal and mechanical properties of the networks were characterized by DMA,TGA and tensile machine,and the de-crosslinking process of the networks under 254 nm UV light was tracked with DSC and UV-vis respectively.Finally,the self-healing and bonding performance of the polymer film was tested.The above studies have shown that the coumarin-based thiol-ene polymers have excellent thermal and mechanical properties and can depolymerize under 254 nm UV light,so it has self-healing properties.However,the highest self-healing efficiency at room temperature was only 50%due to the high Tg of the networks,and the bonding strength was only reduced to 73%.2.To solve the problems of low depolymerization efficiency and high Tg of coumarin systems,a more active anthracene[4+4]cycloaddition system was selected to prepare a high-performance adhesive with high efficiency light response and controllable adhesion.In the chapter 3,anthracene-based thiol-ene networks were designed and synthesized,and their self-healing and controllable adhesion properties were explored.First,the raw material anthracene-9-carboxylic acid was allylated,and then compounded the product with thiols to perform cycloaddition reaction and click chemical reaction under 365 nm UV light to obtain anthracene-based thiol-ene networks with different network densities.The networks of this system had the glass transition temperature close to room temperature,so lower Tg segments could be obtained after depolymerization theoretically.The tracking of the depolymerization process by DSC and UV-vis spectroscopy showed that the networks had strong depolymerization ability at room temperature.In the scratch repair test,the flexible system showed almost 100%self-healing at room temperature.In the final controllable adhesion test,we characterized the adhesive ability of the polymer qualitatively and quantitatively.The adhesive strength was up to 3.45 MPa,the bonding strength was reduced to 20%when exposed to light and the bonding repair efficiency was more than 80%.