Synthesis and properties of novel soluble aromatic polyamides containing 4-aryl-2,6-diphenylpyridine moieties and pendant fluorinated phenoxy groups

Three diamine monomers containing pyridine groups were prepared via the modified Chichibabin reaction of aromatic aldehydes with 4'-nitroacetophenone, followed by reduction with hydrazine hydrate in the presence of Pd/C. Novel aromatic polyamides containing 4-aryl-2,6-diphenylpyridine moieties and pendant fluorinated phenoxy groups were synthesized from these diamines and two fluorinated isophthaloyl dichlorides by the low temperature solution polycondensation in N, N-dimethylacetamide (DMAc). All the polymers are amorphous and readily soluble in strong polar organic solvents such as DMAc, N-methyl-2-pyrrolidinone (NMP), N, N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) at room temperature. The resulting polymers showed glass transition temperatures between 270 and 314 degrees C and 5% weight loss temperatures ranging from 442 degrees C to 475 degrees C, and char yields at 800 degrees C higher than 53 % in nitrogen. These polyamides could be cast into transparent, flexible and strong films from DMAc solution with tensile strengths of 72.5-87.3 MPa, tensile moduli of 2.35-2.87 GPa, and elongations at break of 5.3-9.5 %. The polyamide films exhibited low dielectric constants of 3.21-3.54 (1 MHz), low water uptakes in the range of 1.17-1.38 %, and high transparency with an ultraviolet-visible absorption cutoff wavelength in the 380-391 nm range.