Preparation method of thermosetting polyimide material taking water as solvent

The invention discloses a preparation method of a thermosetting polyimide material only using water as a solvent. The polyimide is prepared from the following raw materials: symmetric dianhydride, asymmetric dianhydride, an active end-capping reagent, symmetric diamine, asymmetric diamine and the like. The specific preparation method comprises the following steps: adding dianhydride and an end-capping reagent into deionized water, and rotating at a constant speed for a certain time by utilizing a magnetic force or a mechanical stirrer at a certain temperature, so that the dianhydride and the end-capping reagent are completely depolymerized into carboxylic acid; cooling to room temperature, adding diamine into the solution, and stirring for a certain time to form a polyimide prepolymer; and putting the obtained prepolymer salt into a closed high-pressure reaction kettle, and carrying out polycondensation reaction on the monomer salt under the conditions of temperature higher than the boiling point of water and