Synthesis Of Dahtm And Preparation And Properties Of Polyimide Films

Polyimide（PI）is widely used in many cutting-edge scientific and technological fields,such as electrical and electrical engineering,military machinery,petrochemical industry,communication equipment,rail transportation,microelectronic devices and engineering material processing,because of its advantages of radiation resistance,corrosion resistance,chemical stability,good electrical insulation,outstanding dielectric properties and mechanical strength.In order to meet the application needs of PI in different occasions in today’s society,the traditional PI should be modified.New varieties,technologies and processes need to be developed to meet the increasingly urgent development needs of high-performance materials.In this thesis,aniline hydrochloride was synthesized from aniline and hydrochloric acid aqueous solution,and then 4,4’-diamino-4’-hydroxytriphenylmethane（DAHTM）was synthesized from aniline and p-hydroxybenzaldehyde in nitrogen atmosphere.The functional groups of the monomer DAHTM were determined by FT-IR.The hydroxyl group was successfully introduced into the skeleton of diamine monomer,and its chemical structure was further confirmed by ~1H NMR and ¹³C NMR.The yield of aniline hydrochloride was 98.9%,its melting point was 195.59℃measured by DSC and its purity was 100%measured by HPLC.The yield of DAHTM was 88.0%,its melting point was 208.79℃measured by DSC.Through~1H NMR,it can be seen that there are almost no impurities in DAHTM and the purity is very high.Three kinds of DAHTM type PI films were prepared by multicomponent copolymerization of DAHTM doped 2,2’-bis[4-（4-aminophenoxy）phenyl]propane and 4,4’-diaminodiphenyl ether with pyromellitic dianhydride,biphenyltetracarboxylic dianhydride and diphenyl ether tetracarboxylic dianhydride,respectively,which were recorded as PI-P,PI-B and PI-O,respectively.Each type of films contains 5 formulas by adjusting the proportion of DAHTM.After the structure of DAHTM type PI films was determined by FT-IR,the effects of different hydroxyl ratio on the mechanical,electrical,thermal,optical,water absorption and surface properties of PI films under the condition of the same polymerization unit were explored by adjusting the relative content of DAHTM in each formula.The details are as follows:With the decrease of the relative content of DAHTM,the tensile strength,dielectric constant and Tg of the films increase first and then decrease as a whole.The difference of ultraviolet and visible light transmittance is very small,and the water absorption and surface energy show an upward trend as a whole.The tensile breaking strength of PI-P,PI-B and PI-O films are 68.1～109.1 MPa,92.9～126.3 MPa and 106.1～148.6 MPa respectively,the dielectric constant is 2.60～3.42,2.88～3.55 and 2.22～2.86 respectively,and Tg is 246.6～265.46℃,267.87～278.80℃and 230.59～256.89℃respectively.So the prepared PI films has high mechanical strength,good insulation and stable thermal properties.The highest transmittance of the films is 88.6～89.5%,87.5～88.9%and 89.4～89.9%respectively,so prepared PI films has good visible light transmittance.The water absorption of the films is 0.38～0.70%,0.84～1.34%and 0.92～1.60%respectively,and the average surface energy is 42.3 m J/m~2,39.0 m J/m~2 and49.0 m J/m~2 respectively.So the hydrophobic and surface properties of the three types of PI films are excellent.In general,the tensile breaking strength of PI-O type PI films can reach 148.6 MPa,with excellent mechanical properties,dielectric constant less than 2.86,dielectric loss less than0.75%,outstanding electrical insulation performance,maximum light transmittance up to89.9%,and good visible light transmittance.The Tg of PI-B type PI films can reach 278.80℃and the carbon residue rate can reach 60.84%at 800℃,the heat resistance is good.The minimum surface energy is 33.9 m J/m~2 and the surface hydrophobicity is excellent.