The process comprises treatment of polyamic acid structure polymer soln. obtd. through polycondensation of dianhydride with 4,4'-diamino diphenyl ether with or without 4,4'-diamino diphenyl methane, in a bipolar amidic solvent. The solution is deposited in successive thin layers on siliconised cellulose paper anti-adherent support. This is followed by drying and high temperature treatment. The polyimidic sheet is electrically insulating, and its onset of thermal oxidation degradation is 440-450 deg C.
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