| The Donor-Acceptor interaction is an intramolecular or intermolecular noncovalent bond interaction similar to a hydrogen bond,which is essentially caused by the difference in charge density between the Donor group and the Acceptor group.In this study,a hydroxyl-terminated small molecule chain extender containing a bisimide ring structure was designed and synthesized,and 1.5-naphthalene diisocyanate was selected to provide a naphthalene ring structure.The electron-donating structure of the naphthalene ring and the electron-withdrawing structure of the imide ring are introduced into the main chain of the polyurethane separately or simultaneously,and thus three series of polyurethanes are synthesized.This work also changed the molecular weight of PTMG in the soft segment of polyurethane.The DPU series containing only the naphthalene ring structure in the molecular chain,the APU series containing only the bisimide ring structure in the molecular chain,and the DAPU series containing both the naphthalene and bisimide ring structures in the molecular chain were synthesized,a total of three series,nine different proportions of polyurethanes.The structure and properties of these polyurethanes were characterized and analyzed,including the composition,molecular weight,molecular weight distribution,nuclear magnetic resonance spectrum analysis,ATR infrared absorption spectrum analysis and hydrogen bonding association of each series of polyurethanes,DSC differential scanning calorimetry,TGA and DTG thermogravimetric analysis,mechanical tensile performance testing,etc.From these,we obtained the influence of the structure of naphthalene ring(D)or bisimide ring(A)on the heat absorption and release properties,thermal decomposition properties and mechanical tensile properties of polyurethanes.In this work,we also found that DAPU series polyurethanes containing a naphthalene ring-bisimide ring(DA)structure in the main chain of the molecule have excellent mechanical tensile properties,so we focused on the DAPU series of polyurethanes and explored the characteristics of its microstructure and the influence of its structure on performance.In this study,the microstructure and properties of DAPU series polyurethanes were characterized and analyzed:(1)We observed and analyzed the micromorphology of DAPU-650,DAPU-1000,DAPU-2000,DPU-1000 and APU-1000 using atomic force microscopy,and combined with the peak fitting of ATR infrared absorption spectrum.The AFM spectrum and HBA of the polyurethanes of each component successfully explains the selfconsistency between the microphase separation structure of each component polyurethane and the degree of hydrogen bond association calculated by the AFM morphology and the ATR peak.(2)We tested the infrared absorption spectra of polyurethanes at different temperatures for each component,focusing on the change of the strength and position of the carbonyl absorption peak of polyurethane between 1760 and 1640 cm-1 with temperature during the temperature rise and fall.We initially explained the absorption peaks of the carbonyl group associated with hydrogen bonding and the carbonyl group of unassociated hydrogen bonding in the four components of DPU,APU,DPU+APU and DAPU,and the variation of temperature with temperature during the temperature rise and fall process.(3)We prepared the DA-650 component polyurethane into a series of gradient DMF solutions and tested them by UV absorption spectroscopy.The test found that there is a UV absorption characteristic peak of DA interaction at the wavelength of 310 nm,and the intensity of the maximum absorption peak increases with the increase of the solution concentration;in addition,the maximum absorption peak intensity and concentration of the ultraviolet spectrum of DAPU-650 are basically a linear relationship between the parties.(4)We selected the polyurethane of DAPU-650 component,and prepared the solution with the concentration of 5 mg/mL~20 mg/mL with DMF,and tested the dynamic light scattering at different temperatures to explore the temperature dependence and angular dependence of the relaxation behavior of polyurethanes containing D-A structures in solution.The results show that:(a)There are two different magnitudes of relaxation time peaks in the DAPU-650 solution at a specific scattering angle.This indicates that there may be two aggregates of statistical average size in the solution;(b)at a specific scattering angle,the relaxation behavior of the two aggregates in the DAPU-650 solution is temperature dependent,and during the heating process and cooling process,the relaxation behavior at the same temperature is not consistent.This indicates that some structures of aggregates in the solution are destroyed with increasing temperature during the heating process;however,these structures cannot be completely recovered as the temperature decreases during the cooling process.In addition,this thesis also studied the mechanical cyclic tensile recovery performance,stress relaxation resistance and annealing heat repair performance of DAPU series polyurethane:(1)At room temperature,we performed a cyclic tensile test with a maximum strain of 500% on the DAPU series polyurethane.The test results show that the deformation recovery performance of DAPU series polyurethane is excellent.The deformation recovery rate of DAPU-650 and DAPU-1000 is basically stable above 98% after the third cycle of maximum strain of 500%.(2)We stretched the DAPU series polyurethane to a maximum strain of 400%,then put them under stress relaxation for 20 h,and measured the deformation recovery rate after fully recovering;then the sample after stress relaxation recovery was annealed at 70 ° C for 5 min,and then fully recovered.The test results show that the DAPU series polyurethanes have very good heat repair performance,especially the DAPU-2000 component.The deformation recovery rate of DAPU-2000 after stress relaxation for 20 h is only 7.3%,but after annealing at 70 ° C for 5 min,The deformation recovery rate can reach 88.5%. |
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