Polyamide acid was prepared from pyromellitic dianhydride (PMDA) and oxydianiline (ODA), and was then reacted with NaH and various kinds of alkyl halides for transformation into alkyl ester. The cast films were imidized as fixed on glass substrate to give Kapton-type polyimide films, and were then carbonized by heating to 900 degrees C. It was shown that the electrical conductivity of the carbonized films decreased with the increase of the size of the leaving group at the imidization. The carbonized films were further heated to 2800 degrees C for graphitization. Their degrees of graphitization and orientation of the graphite crystallites as a function of weight loss at imidization were studied by X-ray diffraction measurements at room temperature and magnetoresistance measurements at liquid nitrogen temperature. Both measurements clearly indicate that the graphitized films prepared from polyamide acid alkyl ester starting from PMDA and ODA have high degrees of graphitization. It was also made clear that, in the case of polyimide having flexible ether linkage, the orientation of the graphitized films did not depend on the size of the leaving group at imidization. (C) 1997 Elsevier Science Ltd. References: 13
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