Rigid-Rod Polyamides from 3,3′-bis-(trifluoromethyl)-4,4′-diamino-1,1′-biphenyl

A diamine monomer with trifluoromethyl groups, 3,3'-bis(trifluoromethyl)-4,4'-diamino-1,1'-biphenyl, is synthesized from 5-bromo-2-nitrobenzotrifluoride with two steps. The model reaction with monofunctional benzoyl chloride at room temperature gives the model compound with a quantitative yield. The results of the model reaction indicate that the amine groups have sufficient reactivity in spite of the presence of electron-withdrawing and bulky trifluoromethyl group at the ortho position. The monomer is polymerized with terephthaloyl chloride and isophthaloyl chloride in N,N-dimethylacetamide (DMAc) or DMAc containing LiCl using pyridine as an acid acceptor at room temperature. All synthesized polymers are somewhat crystalline and colorless. While the meta-linked polyamide (PA2) shows excellent solubility in polar aprotic solvents, the para-linked one (PA1) is dissolved in polar aprotic solvents containing LiCl and concentrated H2SO4. They show good thermal and thermooxidative stability as well as high melting temperatures.