Preparation And Thermal Expansion Behavior Research Of Amide-containing Colorless And Transparent Polyimide Films

The colorless and transparent semi-alicyclic polyimide(CPI)films have good solubility processing,excellent optical transparency and good thermal stability compared with the traditional polyimide(PI)films,which are widely used in the advanced optoelectronic field.The thermal expansion coefficient(CTE)of semi-lipid ring CPI films is increased due to the destruction of the intrinsic conjugation of PI molecular chains,which limits its application in many optoelectronic fields.Therefore,from the point of view of molecular design,rigid amide bonds(-CONH-)and specific groups(such as alkyl substituents)are introduced into CPI molecular structure.While maintaining the inherent solubility and optical transparency of the CPI,CPI is given low CTE characteristics to meet the application of advanced optoelectronic fields for high-performance CPI films.First,novel aromatic diamine monomers containing amide groups and methyl substituents were designed and synthesized,including the monomethyl substituted2-methyl-4,4'-diaminobenzoaniline(Me DABA)and the double substituents substituted2,3'-dimethyl-4,4'-diaminobenzoaniline(MMDABA),and their chemical structures were characterized.Second,the semi-lipid ring CPI films were prepared based on MMDABA and hydrogenated phthalic anhydride(HPMDA)and hydrogenated biphenyl tetramethyl anhydride(HBPDA),including CPI-a(HPMDA-MMDABA)and CPI-b(HBPDA-MMDABA).Performance test results showed that the solubility of CPI resin in organic solvents was improved by introducing double methyl substituents.Meanwhile,the introduction of amide significantly reduced the CTE.Furthermore,the introduction of rigid amide bonds with methyl substituents did not negatively affect the optical transparency and thermal stability of CPI films.CPI-a shows excellent comprehensive properties,including good thermal stability(Glass transition temperature T_g:418?),excellent optical transparency(400 nm transmittance at wavelength T₄₀₀:86.4%;yellowness index b*:0.82;Haze:2.79%)and lower CTE value(46.9×10^-6K).Third,on the basis of the above research work,for the further reduced CTE demand of dimethyl substitution of amide-containing CPI films,we continue to develop the preparation of single-substituted CPI films.Use of 2-methyl-4,4'-diaminobenzanilide(Me DABA),2-chloro-4,4'-diaminobenzanilide(Cl DABA)as diamine monomer,using HPMDA and HBPDA as dihydride monomer,four CPI films were prepared,including PI-I_a(HPMDA-Me DABA)?PI-I_b(HPMDA-Cl DABA)?PI-II_a(HBPDA-Me DABA)and PI-II_b(HBPDA-Cl DABA).The experiment results showed that decreasing the number of methyl substituents did not significantly affect the solubility of the PI resin.The CTE of PI-I_aand PI-II_afilms based on Me DABA is greatly reduced compared with the CPI-a and CPI-b films prepared in chapter 3.For example,The CTE value of PI-I_a(HPMDA-Me DABA)films was 33.4×10^-6/K,significantly lower than that of CPI-a films.In addition,the Me DABA based PI-I_aand PI-II_afilm maintain high optical transparency and thermal stability,the T₄₀₀values were 82.3%and 85.8%,T_ghigher than 340?.