Preparation And Properties Of Polyimide Porous Films And Bulks

Polyimide materials have been widely used in microelectronics industry because of their excellent chemical stability,low temperature resistance,good mechanical properties and excellent dielectric properties.However,with the continuous shrinking of integrated circuits and the signal delay between interconnections,higher requirements for polyimide materials are required.Therefore,the preparation of porous polyimide films with low dielectric constant has become a research hotspot.In this paper,polyimide films with low dielectric constant were fabricated by two different methods,and polyimide porous bulks were prepared,and their properties were studied.In this paper,amino terminated polysiloxane with low molecular weight and terminal amino polystyrene synthesized by disulfide chain transfer agent were synthesized,polyimide-b-polysiloxane block copolymer and polyamide acid-bpolystyrene block copolymer were synthesized by end group reaction.Then two kinds of porous polyimide films were obtained through thermal degradation of polystyrene block and hydrofluoric acid etching of polysiloxane block,respectively.The dielectric properties,thermal properties,adsorbability and surface properties of the porous films were characterized.It is found that the dielectric properties of the films decrease linearly with the increase of porosity,while the thermal stability of the composite films decreases with the amount of polystyrene and polysiloxanes increased.The obtained porous films have better adsorption capacity of water and toluene,and the adsorption capacity increases with the increase of porosity.Moreover,the contact angle of block copolymer films increases with the addition of polystyrene and polysiloxane.When the polystyrene and polysiloxane were eroded,the contact angle decreased,and the surface of the film formed pits structure,and the surface roughness of the films increased.Toluene diisocyanate and diphenylmethane diisocyanate were used as mixed isocyanates to sythesize soluble polyimides with pyromellitic dianhydride.Polyimide porous bulks were prepared by polyisocyanate crosslinking agent.By adjusting the proportion of anhydride and isocyanate,three kinds of components with different crosslinking densities were prepared.Then the porous polyimide bulk is obtained by impregnated water or high pressure reactor.It is found that the pores have uniform size and distributes evenly in the polyimide matrix through the reaction kettle.The porous bulk obtained by the treatment of water needs more time,and its adsorbabilityproperities of water and toluene are better when the crosslinking density of the gel increases.In summary,porous polyimide film has lower dielectric constant,better adsorption property and certain thermal stability.Moreover,low molecular weight polysiloxane and terminal amino polystyrene prepared by disulfide chain transfer agent can effectively improve the solubility of synthetic block copolymers Soluble polyimide was used to synthesize porous polyimide block,avoiding thermal degradation caused by high temperature imidization,moreover,the bulk has good adsorption properties for toluene and water.