▎ 摘　　要

NOVELTY - Preparing graphene modified polyimide composite film comprises (i) uniformly mixing graphite, 98% concentrated sulfuric acid and 85% concentrated phosphoric acid under ice bath conditions, then placing it in an oil bath heated to 50 degrees C in advance, turning on magnetic stirring, slowly adding potassium permanganate to the reaction system, adding hydrogen peroxide to the reaction system after 6 hours of reaction, where the solution turned bright yellow, continuing to react at 50 degrees C for 3 hours and then cooling to room temperature, washing using deionized water, centrifuging, and drying to obtain graphene oxide powder, and (ii) uniformly dispersing prepared graphene oxide powder in a polar organic solvent, obtaining graphene oxide dispersion, adding stir bar and transferring to the oil bath, adding polyisocyanate, heating to 60 degrees C in a nitrogen atmosphere, reacting for 48 hours, and obtaining modified graphene oxide powder after washing, centrifuging and drying. USE - The composite film is useful for outer surface of spacecraft. ADVANTAGE - The method: increases the interlayer spacing; improves the dispersibility of graphene oxide in the polyimide matrix; enhances the film radiation resistance; achieves chain growth; and obtains polyimide with a large molecular weight, which improves the mechanical properties of the film. The composite film has excellent radiation resistance. DETAILED DESCRIPTION - Preparing graphene modified polyimide composite film comprises (i) uniformly mixing graphite, 98% concentrated sulfuric acid and 85% concentrated phosphoric acid under ice bath conditions, then placing it in an oil bath heated to 50 degrees C in advance, turning on magnetic stirring, slowly adding potassium permanganate to the reaction system, adding hydrogen peroxide to the reaction system after 6 hours of reaction, where the solution turned bright yellow, continuing to react at 50 degrees C for 3 hours and then cooling to room temperature, washing using deionized water, centrifuging, and drying to obtain graphene oxide powder, (ii) uniformly dispersing prepared graphene oxide powder in a polar organic solvent, obtaining graphene oxide dispersion, adding stir bar and transferring to the oil bath, adding polyisocyanate, heating to 60 degrees C in a nitrogen atmosphere, reacting for 48 hours, and obtaining modified graphene oxide powder after washing, centrifuging and drying, (iii) uniformly dispersing the obtained powder in a polar organic solvent to obtain a modified graphene oxide dispersion, adding cage polysilsesquioxane (POSS) to the obtained modified graphene oxide dispersion and stirring mechanically for 1 hour to make it evenly mixed, protecting by nitrogen, adding diamine monomer, continuing mechanical stirring under ice-water bath conditions, adding acid anhydride monomer three times at intervals of 0.5 hours after 2 hours, continuing stirring for 6 hours and adding small amount of diamine monomer as linking agent to increase the chain length of the polyimide molecule, continuing mechanical stirring for 6 hours, then transferring to 50 degrees C constant temperature water bath, heating and degrading for 30 minutes to obtain modified polyimide precursor solution, and (iv) uniformly coating the obtained modified polyimide precursor solution on a clean high temperature resistant glass plate, placing in a vacuum drying oven, vacuum defoaming at 25 MPa and pressure for 1 hour, then heating up to 80-120 degrees C at a heating rate of 2 degrees C/minutes for 8-12 hours heat curing treatment, after the heat curing is over, transferring the post sample to the muffle furnace, adopting the programmed heating treatment method, raising the temperature to 150-350 degrees C at a heating rate of 3 degrees C/minutes for 6 hours, then cooling to room temperature naturally, placing the sample in deionized water for 2-5 minutes, and treating the peeled film in a vacuum drying oven at 105 degrees C for 1 hour to obtain modified polyimide film.