Preparation And Properties Of Colorless Transparent Polyimide Films With High Comprehensive Properties

The outstanding overall performance of polyimide（PI）films is critical for their application in the microelectronic and optoelectronic industries.Introducing fluorine structure into PI can effectively reduce the chromaticity of PI film and improve the optical transmittance to achieve colorless and transparency.However,the introduction of fluorinated groups often reduces the thermal stability and mechanical properties of PI films,which becomes a huge obstacle to the development of PI films with high comprehensive performance.In this paper,different series of high-performance CPI films were prepared from the following three aspects:optimization of monomer structure,ternary copolymerization and blending modification.First,the diamine monomer--2,2’-bisfluoromethoxy-biphenyl-4,4’-diamine（TFMOB）containing trifluoromethoxy-OCF3 groups was synthesized.And a series of novel PI films containing trifluoromethoxy groups were prepared from TFMOB/2,2’-bis（trifluoromethyl）biphenyl-4,4’-diamine（TFMB）/3,3’,4,4’biphenyl tetracarboxylic dianhydride（BPDA）tri-copolymer in this paper.The comprehensive performances of the derived PI films could be modulated by the molar ratio of TFMOB/TFMB,and each performance of the PI films was explored in detail.All PI films exhibited excellent overall performance against Kapton PI film（PI-ref）prepared in our lab,especially PI-30,which possessed the best performance,such as remarkable thermal stability(T_5%=581℃and T_g=368℃),outstanding mechanical properties（T_S=195 MPa and TM=3.5 GPa）,ultralow moisture absorption（Ma=0.74%）,lower dielectricity（Dk=2.877 and Df=0.00815 at 10 GHz）and high optical transparency.Other PI films possessed their own unique advantages to meet the special demand of different fields,PI-100 has the best mechanical properties（TS=253 MPa）and ultra-low moisture absorption（Ma=0.50%）.PI-50has the highest flexibility（Eb=27.6%）,PI-0 has the best light transmittance（T450=83.0%）and PI-70 has the lowest dielectric loss（Df=0.00514）.Subsequently,the PI-30 film was used as a colorless and transparent substrate for flexible circuits,which could withstand multiple bends and still maintained excellent electrical stability after 140,000 folding times.Then,on the basis of the above research,commercial fluorinic anhydride--dihydride4,4’-（hexafluoro-isopropene）diphthalic anhydride--6FDA and bisphenol-A dianhydride--BPADA were selected to replace BPDA to further explore the performance changes of CPI films,which was prepared by polymerization of TFMOB and different dianhydrides,and further verified that when TFMOB/TFMB=3:7,the ternary copolymer CPI films prepared had the best comprehensive performance.PI-Ⅰab film:has better transmittance（T450=88.8%）,lower moisture absorption（0.33%）,better low dielectric properties（Dk=2.647,Df=0.00525）;PI-Ⅱab film:excellent transmittance（T450=85.6%）,outstanding low dielectric loss（Df=0.00352）.Finally,cellulose nanocrystals（CNC）and organic modified laponite（LC）were selected to blend with the traditional 6FDA/TFMB-CPI film,and the balance of optical,mechanical and thermal properties of CPI film was studied.It was proved that the addition of two nano-fillers is beneficial to balance the optical,mechanical and thermal properties of CPI composite films.KH550 modified laponite（LC-K）can effectively improve the thermal properties of CPI films,while aminophenyl-POSS modified laponite（LC-P）and CNC can simultaneously improve the thermal and mechanical properties of CPI films without sacrificing too much optical properties of CPI films.(PI-0.2LC-P:T5%=541℃,TS=120MPa,T_M=2.5 GPa,T₄₅₀=86.4%;PI-0.6C:T_5%=537℃,T_S=114 MPa,T₄₅₀=85.0%。)...