| The development of electronic information and technology has brought about the rapid development of electronic information materials.Dielectric materials are an indispensable part of electronic devices.The development of dielectric materials plays a key role in the development of electronic components.Miniaturization and integration of the production process requires that the dielectric material should have a high dielectric constant(or low dielectric constant),low loss,high energy density,good mechanical properties,environment-friendly and easy processing forming and other characteristics at the same time.Polyimide(PI)is a class of high performance polymer materials with high thermal stability,easy of processing,solvent resistance,radiation resistance and low dielectric constant,but in the field of high dielectric or low-dielectric fields,it has received some restrictions.Many researchers have tried to improve or reduce the dielectric constant of polyimides through blending methods and achieved good results.Based on the previous research,?-cyclodextrin and nano-nickel powder were introduced into the polyimide matrix to improve the performance of the composites.The effects of?-cyclodextrin and nano-nickel powder(Ni)on the properties of composites were studied.The paper is divided into the following parts:(1)The polyamic acid(PAA)was synthesized by low temperature polycondensationwith3,3',4,4'-biphenyltetracarboxylicdianhydride(BPDA),4,4'-biphenylenediamine(BPA)and 4,4'-oxydianiline(ODA).The molar ratio of BPDA,BPA and ODA is 2:1:1,the mixed solution of different?-cyclodextrin contents was prepared and the PI/?-cyclodextrin composite film was obtained by means of tape casting and thermal imidization.The performance of composites was tested systematically.The results showed that the dielectric constant of the composites increases greatly as the increase of the content of cyclodextrin,while the breakdown strength does not change too much.The average breakdown strength is 217 MV/m,which is slightly lower than that of pure PI.When the content of cyclodextrin was 50wt%with the annealing of 260?C for 1 hour,the dielectric constant and breaking elongation of the composites reaches 11.47 and 80%,which are about 3 times and30%higher than that of pure PI respectively.The dielectric loss is 0.10(1000 Hz)and the tensile strength was above 100 MPa.When the content of cyclodextrin was 40wt%,the energy density reached a maximum value of 1.46 J/cm~3,which was a greater increase than 0.78 J/cm~3 of neat PI.(2)Polyimide porous membrane was prepared by one-step pyrolysis at high temperature.The effect of?-cyclodextrin on pore-forming was studied by controlling the solid content of?-cyclodextrin and the heat treatment temperature.The results showed that many pores gradually appeared inside the material as the increase of the content of cyclodextrin,which was the most obvious when the content of?-cyclodextrin was 60 wt%.The dielectric constant of the film with the content of 50wt%before the heat treatment drops less than 2.8 and the dielectric loss is about 0.03.Tensile strength is above 100 MPa,it indicates that the mechanical properties are still good.(3)A series of PI/?-cyclodextrin/Ni composites with different nickel contents were prepared by mechanical blending,tape casting and thermal imidization.The effects of?-cyclodextrin and Ni powder on the composites were studied.The results showed that?-cyclodextrin could reduce the dielectric loss and conductivity within a certain range while increasing the dielectric constant at the same time.When?-cyclodextrin content was 30 wt%of PI,the optimum proportion of?-cyclodextrin and Ni powder should be between 1:3 and 1:4.In addition,the addition of?-cyclodextrin also improves the toughness of the PI/Ni composites. |
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