Four polyimide( PI) colloids with different molecular structures were prepared by isocyanate method using biphenyltetracarboxylicdianhydride( BPDA),4,4'-diphenylmethane diisocyanate( MDI), pyromelliticdianhydride( PMDA) and 2,4-toluene diisocyanate( TDI). PI molding powders were obtained after colloids were washed with water and dried. The reaction end time of the seven-membered ring phase was determined by the di-n-butylaminemethod which is 4 h. The PI molding powder were successfully synthesized manifeste...