Preparation And Characterization Of Novel Polyimide Containing Pyridine Heterocyclic Ring

Polyimide(PI)is regarded as a“problem solving expert”due to its excellent comprehensive properties,various synthesis methods and application forms.With the development of the new generation of mobile communication and display technology,polyimide films are playing an increasingly important role in integrated circuits,flexible display(OLED),solar cells and microelectronics.However,due to the special molecular structure,the application of polyimide in some high-tech fields still has some problems.For example,in the field of microelectronics,polyimide is required to have a lower dielectric constant,and in the field of OLED,polyimide is required to have higher optical transparency.Traditional polyimide has been unable to meet the requirements of these emerging fields.Therefore,it is essential to modify traditional polyimide and improve its performance for purpose of meeting the requirements of material application in high technology field.One of the research hotspots at present is the development of excellent organic soluble polyimide with low dielectric constant and good optical transmittance.It is found that the flexible units in the polymer backbone reduce the stiffness of the main chain;The introduction of non-coplanar fluorene can loose the compact accumulation of molecular chains,and the solvent molecules are easy to diffuse between the polymer chains,so as to improve the solubility of materials,while the thermal properties of polymers can also be maintained.The introduction of rigid pyridine ring can improve the solubility of the polymer and maintain thermal performance.Moreover,pyridine has a higher molar refractive index than benzene rings,which can increase the optical transmittance of the material.In summary,this study creatively introduced fluorenyl,pyridine heterocyclic ring and flexible ether bond into diamine monomers,and synthesized three new diamine monomers:9,9-bis(4-(5-amino-2)-Pyridyloxy)phenyl)fluorene,9,9-bis(4-(3-methyl-5-amino-2-pyridyloxy)phenyl)fluorene and 9,9-bis(4-(3-Trifluoromethyl-5-amino-2-pyridyloxy)phenyl)fluorene.Then three new diamines were polymerized with ODPA and 6FDA respectively,and a series of new low-dielectric,organic-soluble polyimide films were prepared through“one-step two-step method”.The chemical structures of the synthesized monomer and polyimide were characterized and analyzed by infrared spectrum,¹H NMR and elemental analysis,etc.The properties of polyimide films were characterized and analyzed by solubility test,universal material tensile testing machine,dielectric constant meter,DSC and TGA,etc.The results are as follows:the target diamine monomer and polyimide with high purity were successfully synthesized.PI films have good solubility in both high boiling point solvents(DMSO,NMP,DMAC)and low boiling point solvents(dioxane,dichloromethane,THF)due to the non-coplanar structure of fluorenyl and the polarization of pyridine ring.At 1 MHz,the PI film also has a low dielectric constant(2.22-3.13)and low dielectric loss(0.0099-0.0275),and its dielectric properties remain stable at high temperatures and high frequencies.The ultraviolet cut-off wavelength(?_cut-off)of these films is located at 348-369 nm,and the transmittance at 450 nm exceeds70%.In addition,all PI films have excellent thermal and mechanical properties.Tg values range from 282°C to 306°C,the thermal weight loss temperature at 5%ranges from 486-553°C,the residual carbon rate at 800°C ranges from 55-63%.The tensile strength,elongation at break and modulus of elongation were 105-129 MPa,6.8-10.4%and 2.38-3.14 GPa,respectively.It is noteworthy that m-methyl substituted pyridinyl PI(3,4)and m-trifluoromethyl substituted pyridinyl PI(5,6)have better comprehensive properties.The new polyimide films with high performance and low dielectric constant are expected to be applied in the field of microelectronics.