CARBONIZATION BEHAVIOR OF POLYIMIDE FILMS WITH VARIOUS CHEMICAL STRUCTURES

Six kinds of polyimide films with different molecular structures were synthesized and carbonized up to 1100-degrees-C. The carbonization behavior of polyimides was followed by measuring the changes in weight, size, and electrical conductivity. Pyrolysis gases evolved on the way to carbonize up to 1000-degrees-C were analyzed by gas chromatography. All films showed appreciable shrinkage and became a black color above 500-degrees-C. No cracks and pores were observed on the films heated up to 1100-degrees-C, even under the scanning electron microscope. A large weight decrease of 35-50% was observed in a narrow temperature range from 500 to 650-degrees-C, which seemed to be due to the departure of CO groups as either CO or CO2. An additional weight decrease occurred gradually above 800-degrees-C, due to N2 departure. A remarkable increase of electrical conductivity along the film surface, more than 2 orders, was observed with the increase in heat-treatment temperature. The polyimide film with a flat molecular structure (PMDA/PPD) gave the highest conductivity: 3.7 x 10(2) S/cm.