Synthesis And Properties Of Schiff Base Type And Containing Triphenylamine And Fluorinated Structure Polyimide Based On Natural Products

Traditional aromatic polyimide possesses excellent thermodynamics,acid and alkali resistance,good tensile properties and many excellent properties,it is widely used in aerospace,electronic devices,military,petrochemical and other fields,playing important roles.However,due to the inherent rigid structure of aromatic polyimide,it is generally difficult to degrade,insoluble,difficult to melt,deep in color,and difficult to process,which greatly limits its application.With the rapid development of the material industry,the properties of traditional polyimide can no longer satisfy the application in many fields in today's society.In order to overcome these problems,the modification of polyimide is urgent.Therefore,we need to overcome its shortcomings without affecting the original excellent performance of polyimide.On this basis,the first part of this article uses the natural product vanillin as the raw material,undergoes the acid-catalyzed reaction with p-aminophenol using toluene to remove azeotropic water,to produce a Schiff base diphenol compound(E)-4-(4-hydroxy-3)-Methoxybenzylideneamino)phenol(VDP),through nucleophilic addition with 2-chloro-5-nitropyridine to obtain dinitro compounds,followed by reduction with sodium sulfide?ammonium chloride system to give a new diamine monomer(E)-4-[4-(5-Aminopyridin-2-yl)oxy-3-methoxybenzylideneamino]-(5-ami-nopyridin-2-yl)-oxybenzene(VDA).We use this diamine monomer as a raw material to polymerize with three commercially available dianhydrides ODPA,PMDA,BPDA,respectively,to prepare three different PI films IPI1,IPI2,and IPI3 through the traditional two-step method of preparing polyimide.The PI film of the IPI series was characterized by infrared spectroscopy,and the characteristic peaks show that it was completely imidized,and the polyimide was successfully prepared.The glass transition temperature of IPI series PI film is 234?238?.In nitrogen atmosphere,the5%weight loss temperature(T_d5)is 526?566?,the 10%weight loss temperature(T_d10)is 555?588?,and the carbon residue rate at 800?is 56.11?58.46%.Due to the difference in dianhydride structure,the optical and mechanical properties of IPI1 with ODPA as the reactant are slightly better than the other two PI films.In terms of mechanical properties,the elongation at break is 6.69?5.68%,the tensile strength is28.59?64.52MPa,and the tensile modulus is 1.66?2.25GPa.In terms of optical performance,the 500nm transmittance is 60.3?77.8%,and the cut-off wavelength is363?402nm.This series of films has good solubility in many common solvents.It is worth mentioning that based on the unique structure of the Schiff base,the PI film of the IPI series can be gradually degraded under acidic conditions.Through ¹H NMR monitoring and analysis,under the condition of 60?and with 1mol/L hydrochloric acid as the degrading agent,the degradation can be basically completed in 20 hours.Based on the monitoring results of ¹H NMR,we proposed the possible mechanism of the degradation process.In the second and third parts,we first synthesized the triphenylamine type dinitro compound 4,4'-dinitro-4''-cyanide using p-fluoronitrobenzene and p-cyanoaniline as raw materials.The triphenylamine dinitro compound(CDN)was reduced by Pd/C and hydrazine hydrate to obtain the triphenylamine diamino compound 4,4'-diamino-4"-cyanotriphenylamine(CDA).Likelise,we synthesized4-[4-(trifluorom-ethyl)phenoxy]-aniline(TFSA)using p-aminophenol and p-chlorotrifluoromethylbenzene as raw materials,and used this compound to react withp-fluoronitrobenzene.Thegenerateddinitrocompound4,4'-dinitro-4"[4-(trifluoromethyl)p-chlorotrifluoromethy(TFDN)was reduced by hydrazine catalyzed under Pd/C to give another new triphenylamine type diamino compound 4,4'-diamino-4"[4-(trifluoromethyl)phenoxy]-triphenylamine(TFDA).The diamine monomer CDA copolymerized with the three commercially available dianhydride monomers ODPA,PMDA,BTDA,respectively,through the traditional two-step process to prepare three different PI films coded CPI1,CPI2,CPI3.The Diamine monomer TFDA and ODA were mixed in a ratio of 8:2,5:5,2:8 to copolymerize with ODPA to obtain three types of films coded FPI1,FPI2,and FPI3.The above-mentioned PI film was also characterized by infrared spectroscopy,showing that it has been completely imidized.On the whole,the films of CPI series and FPI series maintain good thermal properties,and there is no obvious difference between the two series.The glass transition temperature of CPI series PI film is240?252?.In nitrogen atmosphere,the T_d5is 415?487?,T_d10ranging in 495?533?,and the carbon residue rate at 800?47.39?52.98%.whereas,the glass transition temperature of FPI series is 250?277?,T_d5in N₂406?412?,T_d10in N₂431?542?,and the carbon residue rate at 800?53.73?57.62%.The optical properties,solubility,hydrophobicity and mechanical properties of the FPI series are slightly better than those of the CPI series.The reason is that the presence of the bulky trifluoromethyl group effectively weakens the CTC effect and increases the molecular chain spacing.Among them,the 500nm transmittance of CPI series is64.8?78.1%,the cut-off wavelength 362?381nm,while the 500nm transmittance of FPI series is 71.3?79.6%,and the cutoff wavelength 358?386nm.The elongation at break of CPI series is 5.15?8.38%,the tensile modulus is 80.60?86.19MPa,the modulus of elasticity is 2.04?2.43GPa,whereas,the elongation at break of FPI series is 4.32?6.50%,and the tensile modulus is 65.72?75.73MPa,elastic modulus is1.69?1.99GPa.The introduction of fluorine-containing groups into polyimide not only retains the original excellent thermodynamic properties of polyimide,but increases its hydrophobicity and solubility(processability).