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ABSTRACT
A method for the preparation of polyimide nanofoams with high thermal stability, which can be used as dielectric layers in microelectronics is presented. Poly[styrene-co-(4-vinylpyridine)] (PSVP) nanospheres were prepared by emulsion polymerization. The dimension of these particles is between 30 and 40 nm. PMDA-ODA nanocomposite films with various contents of PSVP were obtained by in-situ condensation polymerization in the presence of the nanospheres, casting of polyamic acid solution containing the nanospheres, and imidization. The dispersion of the nanospheres in the films and the morphology of the composite films were characterized by transmission electron microscopy (TEM) and a gas diffusion method. Relative homogenous distributions were observed for the polyimide/PSVP nanocomposite films, which could be ascribed to the formation of poly(amic acid) amine salts between the pyridinyl groups of the nanosphere and the carboxyl groups of the poly(amic acid) before the films being cured. Upon a thermal treatment, the thermally unstable nanospheres undergo thermolysis, leaving pores the size and shape of which are nearly dictated by the initial nanoparticle morphology. The resultant foams were characterized by TEM, TG, density measurements and dielectric constant measurements respectively. The results showed that foams with high thermal stability and low dielectric constant approaching 2.0 could be prepared using this polyimide nanocomposite approach.
ACKNOWLEDGMENT
This work was supported by the National Natural Science Foundation of China (Grant Nos. 59703005).
