Soluble polyimides from unsymmetrical diamine with trifluoromethyl pendent group

4,4′-Diaminodiphenyl ether (4,4′-DDE) is widely used in synthesis of polyimides, but the polyimides synthesized from this diamine are insoluble or have poor solubility depending on dianhydride used. To increase solubility, a new diamine monomer was developed having the same structure with 4,4′-DDE except one trifluoromethyl group at the 2-position of the benzene ring. The new diamine monomer, 2-trifluoromethyl-4,4′-diaminodiphenyl ether, was prepared from 2-chloro-5-nitrobenzotrifluoride and 4-nitrophenol according to Scheme 1. 2-Chloro-5-nitrobenzotrifluoride was reacted with 4-nitrophenol in the presence of potassium carbonate to produce the dinitro compound, which was converted to the corresponding diamine monomer by reduction of the nitro groups.