| Abstract: | Polyamide acid was prepared from pyromellitic dianhydride (PMDA) and p-phenylene-diamine (PDA) and was then reacted with NaH and methyl iodide to transform into methyl ester having various degrees of esterification. Polyamide acid methyl ester was also prepared by the polymerization between PDA and acid chloride of half-ester of PMDA. The cast films were imidized as fixed on glass substrate to give polyimide films having slightly higher tensile moduli than those from polyamide acid, suggesting that higher orientation along the film surface was achieved. It should be noted that the polyimide films prepared by the latter method from the meta-rich configuration had considerably low modulus. The polyimide films were then carbonized by heating to 900°C, and the electrical conductivity of the carbonized films was measured at room temperature. It was shown that the carbonized films from methyl ester have higher electrical conductivity than the films from corresponding polyamide acid. The carbonized films were further heated to 2800°C for graphitization, and their degrees of graphitization and orientation of the graphite crystallite as a function of esterification ratio were studied by x-ray diffraction measurement at room temperature and magnetoresistance measurement at liquid nitrogen temperature. Both measurements clearly indicate that the graphite films prepared from polyamide acid methyl ester have high degrees of graphitization and orientation. © 1996 John Wiley & Sons, Inc. |
