Preparation And Characterization Of Polyimide Containing Porphyrin Units With High Dielectirc Constant

With the development of science and technology,dielectric materials with excellent dielectric properties,excellent thermal properties and excellent mechanical properties have attracted the attention of more and more scholars.Polyimide is one of polymer material with excellent comprehensive properties,but the low dielectric constant of polyimide limits its development.The porphyrin molecule has a very special structure and symmetry,aromaticity,thermal stability,polarization and strong metal coordination ability.In this thesis,three polyimide films were prepared by the method of molecular design,namely,the polyimide PI-a containing porphyrin units and the PI-a/PI-b composite film prepared based on blending(PI-b is common polyimide prepared by BPDA and ODA),PI-c,a polyimide film containing metalloporphyrin units prepared based on copolymerization.The main work can be summarized as follows:(1)Through molecular design,a porphyrin-containing diamine monomer 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin was synthesized,and its structure was characterized by hydrogen NMR spectroscopy.The PI-a film was obtained through a two-step process with porphyrin-containing diamine monomer and BPDA.Infrared spectroscopy shows that polyamic acid was converted to polyimide after imidization.PI-a has excellent dielectric properties.At 10~2 Hz,the dielectric constant of PI-a is 9.0,which is about 2.4 times that of PI-b.Polyimides containing porphyrin units also have low dielectric loss,less than 0.1.The thermal weight loss analysis characterizes the thermal stability of the material.The 5%weight loss temperature of the polyimide containing porphyrin units is above 500?,and the residual rate is 67.6%,showing excellent thermal stability.It has good mechanical flexibility and strength,the tensile strength is 49.0 MPa,and the elongation at break is 2.2%.(2)PI-a/PI-b composite films were prepared by blending PI-a and PI-b,The PI-a/PI-b composite films exhibit excellent dielectric properties.The dielectric constant and loss of the composite film increase with the increase of the mass ratio of PI-a.When the mass ratio of PI-a is 25%,the electrical breakdown strength and energy storage density of PI-a/PI-b composite film are the largest,which are 337.65 k V/mm and 2.66J/cm~3.The composite films have excellent thermal properties,5%weight loss temperature are above 500?,and have a high residual rate.PI-a/PI-b composite films also has excellent mechanical properties,PI-a/PI-b composite film also has excellent mechanical properties.The tensile strength is between 49.0 MPa and 151.6MPa,and the elongation at break is between 2.2%and 9.1%.(3)The porphyrin diamine monomer complexed zinc ion to prepare the zinc porphyrin diamine monomer.The structure of the monomer is determined by the hydrogen nuclear magnetic spectroscopy.The zinc porphyrin diamine monomer is copolymerized with ODA and BPDA,and the PI-c film is obtained through a two-step method.The dielectric constant of polyimide PI-c containing metal porphyrin units is much higher than that of general polyimides,showing excellent dielectric properties.At 10~2 Hz,the dielectric constant of PI-c is 33.2,the value is approximately 3.7 times that of PI-a and 8.9 times that of PI-b.The dielectric loss is 0.04-0.12 at a frequency of10~2Hz-10~5Hz.The electrical breakdown strength is 168.74k V/mm,and the maximum energy storage density can reach 4.18 J/cm~3.The thermal performance of the material was characterized by thermal weight loss analysis.The 5%weight loss temperature of the zinc-containing porphyrin unit polyimide was above 500?,and the residual rate was 66.1%,showing excellent thermal stability.PI-c film also has excellent mechanical properties,the tensile strength is 107.5MPa,the elongation at break is 4.8%,and the toughness can reach 3.11MJ/cm~3.