Preparation of porous carbon films by the pyrolysis of poly(urethane-imide) films and their pore characteristics

Porous carbon films were prepared by the pyrolysis of poly(urethane-imide) films that were prepared by a reaction between phenol-terminated polyuretha ne prepolymer and poly(amide acid) obtained from pyromellitic dianhydride ( PMDA) and 4.4'-oxydianiline (ODA). Upon thermal treatment of the poly(ureth ane-imide) films at 300 to 400 degreesC. the thermally less stable urethane domains decomposed, leaving porous polyimide films. The porous polyimide f ilms were further pyrolyzed at 900 degreesC for 1 h to give porous carbon f ilms. The formation of macropores was confirmed from scanning electron micr oscopy (SEM) of the surface and the cross-section of the films. The size di stribution of the macropore was relatively narrow. With the increase of ure thane content, the size of the macropore increased. The average pore size w as found to be controlled between 0.6 mum and 10 mum by changing the ratio of the imide and the urethane components. It was also revealed from nitroge n adsorption isotherms that macroporous carbon films also contain micropore s that were formed during the pyrolysis of the polyimide films. The progres s of the micropore formation was studied by measuring nitrogen adsorption i sotherms of the carbonized films treated at various temperatures. (C) 2001 Elsevier Science Ltd. All rights reserved.