New aromatic diamines substituted with a trifluoromethyl group in the side chain, 2,4-diamino-3'-trifluoromethylazobenzene, 2,4-diamino-1-[(4'-trifluoromethylphenoxy) phenyl] aniline, and 3,5-diamino-1-[(4'-trifluoromethyl phenoxy) phenyl] benzamide were synthesized and characterized and used to prepare polyimides by a one-step high-temperature polycondensation method. Experimental results indicated that the prepared polyimides possess good solubility in strong organic solvents such as N-methyl-2-pyrrolidinone, NN'-dimethylformamide, and NN'-dimethylacetamide. Homogeneous solutions with solid contents as high as 15-20% can be prepared, which are stable for storing longer than 2 weeks at room temperature. The polyimides exhibited glass-transition temperatures of 249-292 degreesC and good thermal stability. The PI-I-c and PI-IIIc films prepared by casting the fully imidized polymer solutions showed good transparency with cutoff wavelengths at 320-330 nm.