Fluorinated aromatic polyamides and poly(amide-imide)s: Synthesis and properties

A CF3-containing diamine, 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl (1), was synthesized from 4,4'-biphenol and 2-chloro-5-nitrobenzotrifluoride. The imide-containing diacids (Va-b and VIa-l) were prepared by condensation reaction of amino acids, aromatic diamines and trimellitic anhydride. Then, a series of soluble aromatic polyamides (VIIa-f) and poly(amide-imide)s (VIIIa-b and IXa-l) were synthesized from diamine I with various aromatic diacids (IIa-f) and the imide-containing diacids (Va-b and VIa-l) via direct polycondensation with triphenyl phosphate and pyridine. Aromatic polyamides and poly(amide-imide)s had inherent viscosities of 0.60-0.85 dL/g and 0.52-1.44 dL/g, respectively. All synthesized polymers showed excellent solubility in amide-type solvents such as N-methyl-2-pyrrolidinone, N,N-dimethylacetamide (DMAc) and N-dimethylforamide and afford transparent and tough films by DMAc solvent casting. These polymer films had tensile strengths of 87-135 MPa, elongations to break of 8-22%, and initial moduli of 2.0-3.0 GPa. Glass transition temperature of these polymers were in the range of 259-317 degrees C, and the poly(amide-imide)s had better thermal stability than aromatic polyamides. In comparison with the isomeric X series, the IX series exhibited less coloring and showed a lower b* (yellowness index) values than the corresponding IX series.