Synthesis And Properties Of Novel Phosphorus-containing Soluble Polyimide Films

Polyimide(PI)is a kind of macromolecule polymer materials with excellent comprehensive performance.It is widely used in the fields of electronics,aerospace,liquid crystal,packaging materials,membrane materials and so on,because of its excellent thermal stability,chemical resistance and high mechanical strength.However,most of the traditional PI films are difficult to process due to insoluble and difficult to melt.In order to meet the market demand,it is one of the most striking hotspots in the study of soluble PI to improve the processing performance of PI.In this paper,the development and current situation of PI are briefly introduced.A variety of methods for improving the solubility of PI are discussed from the point of view of structural design,and a kind of phosphorus-reactive diamine bis(4-aminophenyl)-9(10-dihydro-9-oxa-10-phosphaphenanthrene-10-phosphoethane)(ADOPPE)was designed and synthesized,and the optimum conditions were studied.The monomer structure was analyzed and identified by means of FI-IR and NMR.In order to improve the polymer solubility while not destroying or reducing the damage to its thermal and mechanical properties,diamine 2-(3-aminophenyl)-5-aminobenzimidazole(i-DAPBI)was introduced.The two diamine monomers were polymerized in a different molar ratio with four aromatic dianhydrides 4,4’-(hexafluoroisopropylene)diphthalic anhydride(6FDA),3,3’,4,4’-biphenyl(BPDA),3,3’,4,4’-benzophenonetetracarboxylic dianhydride(BTDA)and 2,2-bis [4-(3,4dicarboxyphenoxy)phenyl] propane dianhydride(BPADA)by two-step method to prepared four series of polyimides.The apparent viscosity of polyamic acid was determined by DHR rheometer,and the properties of PI films,such as thermal properties,solubility,optical properties,mechanical properties and flame retardancy,were detailed characterized and discussed by TGA,DSC,UV-Vis,universal testing machine and limit oxygen index instrument.The main conclusions are as follows:1 、 The optimum conditions for the synthesis of phosphorus-containing diamine monomers were obtained by orthogonal experiments: the reaction temperature was 130 ℃,the reaction time was 24 h,the amount of p-toluenesulfonic acid used in the catalyst was 1% of DOPO and the amount of aniline is 7 times of the molar amount of DOPO.The yield of the target product was 68% by optimization.The results show that the diamine monomer has been successfully prepared by FT-IR,1H-NMR and DSC.The monomer has high purity and can be used in the synthesis of polymer.2 、 The two diamines of ADOPPE and i-DAPBI with various molar ratios were polymerized with our dianhydrides of 6FDA、BPDA、BTDA、BPADA at room temperature to obtain different series of PI films.The properties of PI films with good film formation were tested and the results show that the introduction of phosphorus-containing structure greatly improves the solubility and flame retardancy of PI,and with the increase of phosphorus content,the solubility is improved obviously;The introduction of dianhydride with flexible structure improves the optical transparency of PI films,but the thermal properties of the polymer has decreased at the same tiame;Imidazole group and biphenyl structure have maintained a certain thermal properties and mechanical properties of polymer.3、The effect of different dianhydride monomers on the properties of PI films was compared under the same molar ratio of diamine monomers.In this paper,ADOPPE: i-DAPBI = 0.2: 0.8 was used to compare the various properties of PI-a-1、PI-b-1、PI-c-1 and PI-d-1.The results show that PI-d-1 has the best solubility and light transmittance in the four PI films,while the thermal properties and mechanical properties are relatively poor.