Preparation And Characterization Of Polyimide/Silica Nano-Hybrid Films

Polyimide (PI) that serves as a typical kind of engineering polymer material has been used widely in the aerial, nuclear and microelectronic industries because of its outstanding characteristics, such as excellent thermal stability, relatively high tensile strength and modulus, and, especially, preeminent electrical properties including low dielectric constant. But the facts that the pure polyimide has many disadvantages, such as high wettability, thermal expansivity and moreover, that some applications prefer a more rigid claim, demand the higher performance polyimide. Usually, inorganic materials have some unique characteristics compared with organic materials. It proved by experiments that incorporating inorganic ingredient into organic matrix resin would produce a new kind of material that presented characteristics and properties of the both two moieties.In this paper, a kind of nano-hybrid polyimide/silica matrix resin was synthesized by the hydrolysis and condensation of methyl-triethoxysilane that served as the precursor of the inorganic moiety and produced the nano-particle of silica in-situ in the polyamic acid solution through sol-gel reaction, and then the composite film was prepared. In order to improve the molecular force between the organic and inorganic phase, a coupling agent was used in this work. The variation of the molecular weight of Polyamic acid (PAA) with the solid content of PAA and the stock time was analyzed by GPC. The chemical structure and morphology of the films were characterized by Fourier Transform Infrared Spectroscope and Atomic Force Microscope respectively. And the properties such as water absorbability, thermal stability, mechanical property and electrical properly with the inorganic component content and the morphology between the two phases were discussed. It turned out by the experiments that incorporating inorganic moiety into polymer resin, the variation of SiO2 content and the character of interfaces between the two phases had great effects on the properties of the hybrid film compared with those of the non-dopedpolyimide. And it showed that there existed the intensive action between the two phases with the coupling agent added into the polyimide/silica composite system, and that it would play a certain role in improving the miscibility and interfacial morphology between the two phases, and in reducing the size of the inorganic particle. It also showed that the water absorbability decreased with the SiO2 content, and that no apparent change would be brought about in thermal decomposition temperature as the inorganic component was added into polyimide resin. In this article, the electrical properties of the films including dielectric property, insulating properly and the corona-resistant property were emphasized.