Study On Synthesis And Properties Of Intrinsically Black Polyimide

With the rapid development of high-tech,especially microelectronics,optoelectronics and other industries,polyimide(PI)materials have attracted more and more attention and applications,and the market requirements for the performance of PI are constantly increasing.However,the traditional PI film has less hiding power to the underlying circuit because of its high transparency,which limits its application in the electronic industry such as integrated circuits.Therefore,black PI films with excellent comprehensive properties,opaque and low visible light transmittance are favored by people.In this paper,indoleketone diamine with large planar structure was designed and synthesized,and the relationship between structure and properties of homopolymerized black PI and copolymerized black PI,such as light transmittance,thermal properties,mechanical properties and so on,were studied.First of all,based on the preparation of intrinsically black PI,a diamine monomer(E)-6,6'-bis(4-aminophenyl)-1,1'-bis(2-ethylhexyl)-[3,3'-biindolinylidene]-2,2'-dione(IID)with large coplanar and D-A conjugated structure was designed and synthesized by molecular design in this paper.The structure of the product in each step was characterized and confirmed by nuclear magnetic resonance spectroscopy(¹H NMR and¹³C NMR)and infrared spectroscopy(FT-IR).In addition,through theoretical calculation,it is known that IID has the characteristics of electron-rich and strong electron-giving ability,which is beneficial to the strong charge transfer effect and intermolecular“p-p”stacking effect of PI,thus effectively reducing the light transmittance of the PI films.Secondly,the novel diamine IID designed and synthesized was polymerized with four commercial dianhydrides:3,3',4,4'-biphenyltetra-carboxylic dianhydride(BPDA),3,3',4,4'-benzophenonetetracarboxylic dianhydride(BTDA),4,4'-oxydiphthalic anhydride(ODPA),pyromellitic dianhydride(PMDA),respectively,and the homopolymerized black PI of IID-PI series was synthesized.Their structure and properties were characterized by Fourier transform infrared(FT-IR),UV-visible light analysis(UV-vis),mechanical tensile test and so on.The results showed that the cutoff wavelength was above 670 nm,and the light transmittance of IID-PI films at 700 nm was only 2.9%?4.3%.The glass transition temperature values were from 348 to 390°C.The5%and 10%weight loss temperature values were 439?452°C and 472?478°C,respectively;and the residual weight retentions at 800°C were 58%?62%.The tensile strength at break was between 48.24 and 65.01 MPa;the elongation at break was3.67%?9.35%and the tensile modulus was ranged from 0.79 to 1.72 GPa.The water absorption rates were 0.41%?1.05%;the contact angle was 72.7?79.4°,and the adhesion grade was 0?1 grade.This showed that the obtained IID-PI films had high blackness,low light transmittance,outstanding heat resistance,low water absorption,excellent chemical resistance and adhesion.Finally,to avoid the brittleness tendency and improve the mechanical properties of black PI,we polymerized black PI with different molar ratios of IID and4,4'-oxydianiline(ODA:IID=1:9,3:7,5:5,7:3,9:1)to obtain copolymerized black PI.The structure and properties of PI-O films were characterized by FT-IR,UV-vis,mechanical tension and other tests.The results indicated that the cutoff wavelength of PI-O films was in the range of 630?672 nm,and the light transmittance at 650 nm was less than 2.3%.The glass transition temperature values were 403?426°C;the 5%and 10%weight loss temperature values were in the range of 419?476°C and 441?532°C,respectively;and the retention rate of residual weight at 800°C was up to 63%.The tensile strength at break was increased from 74.16 to 130.82 MPa;the elongation at break was increased from 3.95%to 12.01%,and the tensile modulus was ranged from1.13?1.62 GPa.The water absorption rate was 0.51%?0.90%;these PI films were insoluble in various solvents,but became easier to hydrolyze in Na OH solution,and the adhesion grade was increased from 1 to 0.The results suggested that with the increase of ODA content,PI-O films still maintained high blackness and low light transmittance.In addition,the properties of black PI,such as thermal properties,mechanical properties,adhesion and so on,had been improved.