Preparation And Properties Of Polyimide Materials Containing Amide Bonds,Imidazole And Pyrazoline Heterocyclic Structures

With the rapid development of aerospace and aviation,high frequency telecommunication,sophisticated microelectronics and flexible display industries,polyimides（PIs）as“problem solver”have become increasingly important.The structural modification of PIs has also been motivated by these emerging technologies,which put forward higher requirements on the performance of PIs to meet new needs.Aiming at the dielectric properties,gas separation performance and biomedical properties,three diamines containing amide,imidazole and pyrazoline,respectively,were synthesized in the work of this thesis,and the“structure-properties”relationships of these three series of PIs have been investigated comprehensively.In the part of the first series of PIs,1-chloro-4-nitrobenzene and 2-chloro-5-nitrobenzotrifluoride,respectively,were used as raw materials for the synthesis of two analogous diamines,ANTP containing amide bonds and ANTPB containing amide bond and trifluoromethyl,through three steps,which included nucleophilic substitution,amidation and reduction by hydrazine catalyzed by Pd/C.The two diamines ANTP and ANTPB were used to polymerize with four commercial dianhydrides PMDA,BPADA,BTDA and BPDA,and the prepared PIs were coded as the PI-Ax and PI-Tx series,with PI-Ax referring to the PIs derived from ANPB,and PI-Tx referring to the PIs derived from ANTPB,respectively.Due to the introduction of trifluoromethyl,PI-Tx series have a slight reduction in thermal stability as compared with PI-Ax series,but still maintained good thermal properties,with T_g ranging in 236-280℃,T_d5 ranging in 413-485℃.Furthermore,the increase in V_w values(PI-Tx:261.77-432.67 g·mol^-3 Vs PI-Ax:242.96-413.86 g·mol^-3)imparts PI-Tx with better solubility,higher optical transmittance as indicated T₅₀₀（PI-Tx:53.9%-83.6%Vs PI-Ax:33.4%-75.1%）and better hydrophobicity as indicated by contact angle（PI-Tx:83.9-100.0°Vs PI-Ax:70.7-88.8°）.It was found by DFT calculation on the polymer repeat units that PI-Tx（E_g:2.56-3.44）has a larger energy gap value than PI-Ax（E_g:2.21-3.19）,and more distorted conformation obtained by MD simulations,resulting in lower CT interaction and higher optical transparency.The presence of CF₃ units in the polymer chains endows PI-Tx with lower dielectric constantε’and dielectric lossε’’than commercial Kapton HN at the same measurement frequency and temperature.In the part of the second series of PIs,benzoyls and 2-chloro-5-nitrobenzaldehyde were used as raw materials to synthesize the imidazole-containing diamine monomer DHA via a Debus-Radziszewski condensation reaction,nucleophilic substitution and reduction.Three PIs were prepared by copolymerize DHA and ODA with molar ratios10:0,7:3,and 5:5,towards commercial dianhydride ODPA,coded as PI_10-0,PI_7-3 and PI_5-5,respectively.There PIs showed T₅₀₀ in the rang of 75.1%-84.2%andλ₀ in the range of 374-385 nm,and higher optical transparency of PIs was observed with increasing content of DHA.As verified by wide angle X-ray diffraction and the spatial structure of the molecular chains,the bigger percentage of ODA in the polymer chain led to less spatially distorted conformation,resulting in lower optical transparency of the polymer.The PIs exhibited T_g ranging in 224.2-246.7°C,T_d5 ranging in 461.75-473.87°C and T_d10ranging in 488.46-495.32°C,T_S in the range of 44.98-94.71 MPa,T_M in the range of 1.95-2.38 GPa,and E_b in the range of 10.12%-12.71%.In addition to the retained thermal stability and mechanical properties,the PI materials showed good solubility in organic solvents.Five PIs were chosen from the above two series to conduct molecular simulation to explore the relationship between PIs composed of different repeat units and gas separation properties in a view to gain insight into their multi-component gas separation mechanisms.The simulation results show that ANPB-PMDA derived from PMDA has strong hydrogen bonding and cohesive energy effects that increase intermolecular chain interactions and reduce molecular chain mobility of the polymer due to the intermolecular hydrogen bonds formed by the amide units（-C=O···H-N-）which inhibit the penetration of small molecules into the material and their diffusion within the film.Bulky imidazole pendant groups in DHA-ODPA were found to restrict the backbone migration and disrupt molecular chain stacking,resulting in increasing small molecule solubility rates and permeation coefficients.In contrast,the complementary hydrogen bond（-N-H···N=C）in the imidazole ring contributes to the selectivity of the retention gas for CO₂/CH₄,CO₂/O₂,H₂/CH₄ and H₂/N₂ with separation coefficients of 1.3584,1.2029,11.1672 and 2.7059,respectively.In the part of the third series of PIs,the diamine monomer DPE with a pyrazoline structure was synthesized from the biomass product vanillin and 4-hydroxyacetophenone via the Claisen-Schmidt ester condensation to give chalcone,cyclization with hydrazine to form pyrazoline ring,nucleophilic substitution and reduction.DPE was copolymerized with three commercial dianhydrides BPADA,ODPA,PMDA,following thermal imidization to prepare PI films.Experimental results showed that pyrazoline structure imparts polyimide with good transparency,with T₅₀₀exceeding 60%.The polymers show T_g ranging in 254.5-328.6°C and T_d5 ranging in405.69-433.67°C,T_M ranging in 1.87-5.79 GPa,T_S and E_b ranging in 76.56-145.76MPa and 8.73%-14.41%,respectively.In addition,the PI films were all amorphous by wide angle X-ray diffraction analysis,and had excellent organosolubility.The PI films were hydrophilic with contact angles less than 90°.The polymer materials were found as physiological inert and showed in vitro antibacterial effects.DPE-BPADA and DPE-PMDA showed good antibacterial effects against Escherichia coli,while DPE-ODPA showed good antibacterial effects against Staphylococcus aureus.The different antibacterial effects towards different bacterial of pyrazoline-containing PIs may originate from different dianhydride moieties in the polymer chain which lead to changed LUMO values.