Synthesis And Characterization Of Shape Memory Cross-linked Polyurethane With Photo-thermal Response

Shape memory polymers(SMPs),after sensing external stimuli,can spontaneously drive and return to their original shape in response to changes in the external environment.However,single-function thermal SMPs can not meet the complex needs of practical applications,and it is difficult to achieve higher requirements for practical applications.This prompted researchers to actively develop new smart materials,so that a material can not only achieve the shape memory function at the same time,but also take into account other features,combined with two or even a variety of response characteristics.However,most researchers currently introduce functional monomers in a doping manner,and they are still essentially thermally induced SMPs,and the doping of functional substances will definitely have a negative impact on the properties of the material.In this case,a variety of shape-memory polyurethanes with photo-thermal staging-responsive SEM project project were synthesized through experimental design.Firstly,this project adopts solution polymerization to synthesize cross-linked A-SMPUs with photo-thermal responsive by using 4,4'-dicarboxyazobenzene monomer,PCL4000,HDI and cross-linking agent glycerol as raw materials.The results show that with the increase of azobenzene content,the UV light response of A-SMPUs become more obvious,and P1 with the highest content of Azoa have a photo-thermal staging-responsive SEM.The microphase separation structure of A-SMPUs is composed of semi-crystalline PCL soft phase and azobenzene hard phase.The increase of the content of azobenzene hard segments in turn affect the soft segment crystallinity of PCL.The chemical cross-linking of glycerin brings stable network structure and good thermal stability to A-SMPUs.All samples of A-SMPUs exhibite good triple shape memory performance with up to 97% shape fixity and 95% shape recovery.Secondly,this project had used 4,4'-dicarboxyazobenzene monomer,MDEA,HDI as raw materials,TEA as a cross-linker,prepared light-thermal response triple shape memory LAPUs.The results of FT-IR,NMR,and volumetric measurements demonstrate that the cross-linked structures of LAPUs have been successfully synthesized.The results of TG and DSC tests show that the cross-linker TEA enhances the thermal stability of the material to some extent?In this case,the reason why causes this sitation is that the rigidity of the system is enhanced and the heat resistance of the system is improved due to the increase of crosslinking degree.XRD test results show that with the increase of crosslinker content,the crystallization ability of LAPUs become stronger.The results of SEM and AFM morphology tests show that LAPUs are composed of MDEA soft phase and Azoa hard phase,and the Material develops from brittle fracture to ductile fracture.The LAPUs were tested with an UV light apparatus and showed that the LAPUs have excellent UV light responsiveness.All the samples were able to flexibly respond under UV light and returned to their original shape after heating,with photo-thermal staging-responsive SEM.Finally,this project also had used 4,4'-dihydroxyazobenzene monomer,MDEA,HDI,1,3-propanesulfonic acid(1,3-PS)as raw materials,TEA as a cross-linker,to prepare photo-thermal responsive LRPUs-PS of triple-shape memory cross-linking system.Through XRD tests,the test results show that the crystallization property of the LRPU-PS system are weak.TG?DSC and DMA examinations shows that the introduction of 1,3-PS reduced the thermal stability of the system to some extent.The morphology of LRPU-PS was analyzed by SEM and AFM,showing that LRPU-PS has a two-phase separation structure.The soft segment MDEAPS enhances the rigidity of the system segment and separates the hard and soft segments,which has a certain enhancements on the toughness of the material.Observing the liquid crystal characteristics of the sample with a POM plot,it can be seen that the LRPU-PS has a good liquid crystallinity,and its liquid crystal transition is in accordance with the test results of the DSC.Using DMA to test the shape memory performance,the results show that LRPU-PS has good shape memory performance,and the shape recovery rate increases with the increase of MDEAPS content.UV test results show that the absorption region of Azobi's transition is in the near-ultraviolet region and visible light region.At this time,the transition from trans-structure to cis-structure will occur.To observing macroscopical responsiveness undergo irradiation of UV light,we used UV test and the result showed that the shape of LRPU-PS will distort under UV light of a wavelength of 365 nm.