Study Of Photo-Thermal Responsive Dynamic Covalent Polymers

Thermoplastic polymers are easy to process and be recycled,however,they are not resistant to solvents and high temperature,and are prone to aging.In contrast,thermosetting polymers are resistant to solvents,corrosion and high temperature,but not easy to be recycled.Scientists have long been working to develop intelligent new materials that combine both advantages,with promising applications in aerospace materials,intelligent sensors,drug delivery,molecular machines,artificial muscles and 3D/4D printing materials.In recent years,the introduction of dynamic covalent bonds into the cross-linked polymer system makes it possible to tackle this problem.Dynamic covalent bond is a kind of reversible bond breaking and recombination under certain conditions.Polymer crosslinking with dynamic covalent bond shows the characteristics of thermosetting polymer under conventional conditions.When stimulated by external conditions,such as heating,illumination,mechanical force,magnetism and pH,the dynamic covalent bond in the polymer network can be opened,the crosslinking degree can be reduced,resulting in movement and rearrangement of chain segments,thus showing more characteristics of the thermoplastic polymer.At present,the dynamic bond exchange reactions for the vast majority of reported dynamic polymer networks are triggered by in-situ heating.If the photothermal building block is further introduced,the advantages of remote control,directional response and energy control of optical stimulation can be utilized to further expand the application scenarios of dynamic polymer networks.The twelve carbon-bonded carbolong complex developed by our group in recent years has a good photothermic performance under the irradiation of near-infrared light(808 nm),and the near-infrared light has such characteristics as strong penetrability,low energy and good biocompatibility.Therefore,it is a new type of photothermal building block with excellent performance.It is expected to integrate this carbolong complex into dynamic polymer networks,to construct a novel dynamic polymer network with multiple responses of light and heat.In this thesis,we developed a new type of dynamic covalent compound BPID based on thermal response free radical exchange reaction.On this basis,carbolong complex and dynamic covalent bond compound BPID were introduced into polymer crosslinking to obtain a new type of dynamic polymer network with multiple responses of light and heat,and its functions of thermal responsiveness,optical responsiveness,self-healing and shape memory were further studied.The contents of this thesis are as follows:The chapter 1,combined with the research content of this thesis,the carbolong complex,dynamic covalent bond,dynamic covalent polymers and self-healing materials are briefly introduced.Finally,the concept and purpose of this paper are expounded.In chapter 2,a novel BPID dynamic covalent compound was synthesized for the first time and photothermal-responsive polyurethane networks were constructed.Studies have shown that such cross-linked polymers have the advantages of both thermosetting polymer and thermoplastic polymer.They are mainly thermosetting at room temperature;while turn to be thermalplatic under high temperature or NIR ph oto-irradiation on account of the polymer chain breaks and rearrangement caused by the generation of free radicals of BPID.In chapter 3,BPID dynamic covalent compound with four hydroxyl groups was synthesized,and then photothermal-responsive dual cross-linked polyuretha.nes with this new BPID moiety were constructed.It has been shown that the dual crosslinked polymers can achieve microscopic self-healing repeatedly after many times of stretching and photothermal stimulation,and has good shape memory capacity.In addition,the dual cross-linked polymers have the characteristics of force chromatism.In chapter 4,polyurethane network is constructed by using the polybutadiene oligomers and carbolong complex into the crosslinked polymer backbone,and the second generation Grubbs catalyst is introduced into the crosslinked polyurethane film by swelling.The study shows that after near-infrared light irradiation,the trace catalyst in polyurethane film induces the olefin metathesis reaction,which leads to the chain breaking and rearrangement,and finally realizes the self-healing of the material.The mechanical properties of the healed material remain good.In chapter 5,the main contents research prospects of this thesis are summarized.