Study On Chemical Structure Regulation And Dielectric Properties Of Polyimide

The dielectric constant of polyimide is closely related to molar polarization and molar space volume.The dielectric constant of polyimide can be effectively reduced by destroying the symmetry of molecule chain or reducing the polar structure of molecule chain.In this paper,the molecular structure of polyimide is regulated by different modification methods,so that it can reduce its dielectric constant while maintaining its thermal stability,mechanical properties and other excellent properties.Firstly,two dianhydrides with different structures and two diamines with different structures were selected as monomers to synthesize polyimides,among which dianhydride was pyromellitic dianhydride and cyclobutane tetracarboxylic dianhydride,diamine was 4,4’-diaminodiphenyl ether and 2,2’-bis(trifluoromethyl)diaminobiphenyl.Firstly,the optimum synthesis scheme was determined through the study of homopolymerization conditions and film forming process.Then,the basic properties such as viscosity,dielectric constant and water absorption were characterized and tested,which provided basic data for later modification research.Then a series of polyimide films were synthesized by copolymerization,and the ratio of the lowest dielectric constant was chosen as the optimum ratio.The minimum dielectric constant is 2.56(1 MHz),the reasons for the low dielectric constant were analyzed.The thermal stability,mechanical properties and saturated water absorption of low dielectric constant polyimide films were tested and characterized.Finally,another modification method-blending modification was used to control the structure of polyimide in order to reduce the dielectric constant of the material.Blending polymerization is mainly carried out on the basis of the synthesis of binary homopolyamic acid.According to the monomer ratio of copolymerization and changing the molar ratio of homopolyamic acid,a series of blended polyimide films corresponding to copolyimide are prepared,and their dielectric constant is characterized and tested.The lowest dielectric constant ratio is selected,its dielectric constant is 2.68(1 M).By comparing the two methods mentioned above,the optimum modification method was selected,and finally it was determined that the reduction of dielectric constant was more obvious by copolymerization regulation.Finally,the thermal stability,mechanical properties and saturated water absorption werecharacterized and tested.