| With the continuous progress and development of technology,flexible display technology has undergone rapid development in recent years.The key components of flexible display substrate materials,such as optical performance,thermal stability,and flexibility,also need to be improved accordingly.Due to the charge transfer complex(CTC)in the molecule of traditional polyimide,its light transmittance in the visible light wavelength range is low,which can not meet the requirements of flexible display device substrate in optical performance.Therefore,relevant research is needed to find polyimides that can not only meet the requirements of optical permeability,but also maintain high temperature resistance and low thermal expansion coefficient.This paper presents the design and synthesis of diamine monomer 1-(4-aminophenyl)-1,3,3-trimethyl-2,3-dihydro-1H-inden-5-aminoindene(3a)containing indene groups,as well as diamine monomer 4-amino-N-(4-(5-(4-aminobenzamide)-1,3,3-trimethyl-2,3-dihydro-1H-inden-1-yl)phenyl)benzamide(3b)modified with amide bonds,Then,diamine monomer3 a and diamine monomer 3b were polymerized with commercial dianhydride H-PMDA in the molar ratio of 100:0,75:25,50:50,25:75,0:100 in one step,and the polyimide films of CPI-1,CPI-2,CPI-3,CPI-4,and CPI-5 were prepared by tape casting and scraping film method.It was confirmed that diamine monomer 3a and diamine monomer 3b were successfully synthesized by NMR,IR,elemental analysis and other characterization methods.Then the polyimide film was characterized by IR and wide-angle XRD,and it was found that the introduction of amide bonds would promote the formation of intermolecular hydrogen bonds.Then,a series of studies were conducted on the properties of PI thin films using characterization methods such as ultraviolet visible absorption spectroscopy(UV),thermogravimetry(TGA),thermomechanical analyzer(TMA),electronic universal material testing machine,dielectric analyzer,contact angle,and water absorption testing.The results are as follows: the transmittance of all PI films at 400 nm ranges from 82.6% to 83.33%,the5% thermal weight loss temperature ranges from 436 to 506 ℃,and the glass transition temperature ranges from 363 to 386 ℃,exhibiting good optical transmittance and thermal stability.At the same time,all polyimides have good mechanical properties and good solubility.From the experimental data,it can be concluded that with the increase of the molar ratio of diamine monomer 3b,the content of hydrogen bond between PI molecules increases,the interaction between molecular chains increases,the molecular crystal plane spacing of polyimide films decreases,and the density,glass transition temperature,dielectric constant,etc.increase.After comparative analysis,it was found that CPI-5 has the best overall performance,with a brightness of 95.11,a yellowness of 4.41,a transmittance of about 82%at 400 nm,Tg of 386 ℃,Td5% of 436 ℃,and CTE of 47.75 ppm/K.In addition,in order to further improve the dimensional stability and thermal stability of transparent polyimide films,we polymerized the diamine monomer 3b with CBDA to obtain3 b CBDA polyimide.Compared with CPI-5,it has a higher glass transition temperature(Tg=400 ℃),better optical properties(T400=76.04%),and a relatively low CTE value(46.05ppm/K).The effect of reducing CTE is not as expected,and further research is needed to seek CTE values that can maintain both optical and thermal properties while also matching with commonly used conductive materials-copper foil.The results of this experiment provide a certain idea for the follow-up study of high temperature resistant transparent polyimide and the modification of PI. |
PDF Full Text Request