Preparation Of Side-chain Azobenzene Polymers Containing NHS And Study On Their Photodeformation Properties And Recovery

Nowadays,a variety of light-driven azobenzene polymer flexible actuators with excellent photodeformation performance and good stability have been developed.In these systems,the presence of an appropriate level of cross-linked network plays an important role in macroscopic deformation because it is responsible for transmitting the photomechanical forces generated by the azobenzene mesogen throughout the network.However,the flexible actuator with chemical cross-linking system obtained by the traditional polymerization method is difficult to be reprocessed because it is insoluble and infusible,which limits the further application and development of photodeformable azobenzene polymer materials.Therefore,it is essential to improve the processability by developing new cross-linking methods and new azobenzene polymers.This article is devoted to the recycling of azobenzene liquid crystal polymer in a simpler way.Therefore,starting from molecular design,azobenzene liquid crystal polymer containing side chains containing easily cross-linked N-hydroxysuccinimide?NHS?.Amine is the post-crosslinking agent,and the recovery and reconstruction of the azobenzene polymer fiber based on the chemical post-crosslinking is finally achieved.The structure-performance relationship of the obtained azobenzene polymer,as well as the photodeformation performance and recycling process of the polymer fiber after cross-linking were systematically studied.The main research contents and results are as follows:?1?First,a series of acrylic azobenzene monomers containing N-hydroxysuccinimide and flexible spacers with different lengths?m=2,6,10?were synthesized,which were then co-existed with MMA by traditional free radical polymerization a series of azo copolymers with different copolymerization ratios?azobenzene content calculated from NMR results 18%,30%,51%,61%,100%?were successfully prepared.And through 1H NMR,TGA,DSC,POM and UV-vis,its structure,thermal stability,phase transition behavior and photo-isomerization behavior were thoroughly studied.The results show that the series of azobenzene liquid crystal polymers were successfully obtained in only five steps of synthesis,and the nuclear magnetic results were consistent with the theoretical results,and the yield will decrease as the proportion of azobenzene increases;the series of polymers are thermally stable and good,and the thermal decomposition temperature at 5%weight loss is above 267^?;when the homopolymer's flexibility spacer is long?m=2,6,10?,it has obvious bi-enantiomeric smectic liquid phase;the azobenzene polymer solution has good reversible photoisomerization ability and can be well circulated.?2?Azobenzene polymer fibers were obtained by melt spinning method,and cystamine dihydrochloride was used as a post-crosslinking agent to successfully obtain crosslinked polymer fibers.The process was characterized by infrared,and the orientation,solubility,thermal stability,mechanical properties,light responsiveness and fatigue resistance of post-crosslinked fibers were also studied.The results show that the polymer fibers are successfully post-crosslinked;the fiber orientation is good and has nothing to do with crosslinking;compared with uncrosslinked fibers,crosslinked fibers no longer dissolve in common organic solvents and can undergo glass transition when the temperature?T_g?is kept unchanged for 30 minutes,the solvent resistance and thermal stability of the cross-linked fiber bing significantly improved;compared with the previous typical chemical cross-linked fiber mechanical properties have been greatly improved?for example,the tensile strength of CP6-51%fiber can reach 26 MPa,and the elastic modulus can reach 549 Mpa?which will make it have good application prospects in artificial muscles and optical drives;this series of fibers has fast and the reversible light responsiveness,such as CP6-51%fiber ultraviolet and visible response time is only 24 s and 26 s,and UV-Vis can be cyclically deformed more than100 times under alternating irradiation,which also shows that the fiber has excellent mechanical properties and fatigue resistance.?3?Since the disulfide bonds in the post-crosslinking agent cystamine can be broken through a simple redox,the successful recovery and reconstruction of cross-linked polymers and polymer fibers was achieved on this basis.The experimental results show that the polymer and polymer fibers after cross-linking can be recovered in the presence of the reducing agent tributylphosphorus,and can be oxidized and reconstructed by using H₂O₂.The infrared peak results in the thiol peak will disappear and can reappear insoluble and infusible,and the polymer fiber will restore the light responsiveness again,and the process is highly repeated.And for the fiber,the post-crosslinking process only occurs on the surface of the thin layer,so the fiber can also be recovered and reconstructed by combining the reduction reaction with the post-crosslinking process,and also through the change in the solubility of the fiber,and infrared and Nuclear magnetic tracking of the process showed that the polymer fiber can also be recovered and reconstructed through the above process,and after repeating the above process 5 times,the polymer still contains 31%N-hydroxysuccinimide,and the fiber obtained through recovery and reconstruction each time still has the same photodeformation behavior as the first cross-linked fiber.The NMR results indicate that the content of N-hydroxysuccinimide can be predicted by the number of repetitions to predict the degree of cross-linking and light of the polymer fiber.Deformation effect.A model reaction was also designed using cysteamine as a post-crosslinking agent to verify the above reduction process,and the results were completely consistent with expectations.