Synthesis and characterization of thermally stable quinoxaline-based polyamides

A novel diacid monomer, 2,3-Bis-[4′-(4″-carboxymethylene)phenoxyphenylene] (BCPPQ), featuring a rigid cardo-type quinoxaline core and flexible ether-methylene linkages, was synthesized via a two-step process from 4,4′-difluorobenzil. Structural confirmation was achieved through FT-IR, 1 H and 13 C NMR (including DEPT), and HRMS. BCPPQ was then polymerized with various aromatic diamines using triphenyl phosphate in an NMP/pyridine/LiCl system to yield a series of high molecular weight polyamides. These polyamides exhibited excellent solubility in polar aprotic solvents (e.g., DMF, DMAc, NMP) and showed inherent viscosities ranging from 0.16 to 0.25 dL/g. FT-IR analysis confirmed amide bond formation. Thermal studies (TGA/DSC) revealed high thermal stability with decomposition temperatures above 395 °C and glass transition temperatures between 173 and 198 °C. XRD patterns showed broad halos, confirming their amorphous nature. The incorporation of a bulky quinoxaline unit and flexible linkages improved solubility without significantly compromising thermal performance, suggesting their potential for high-performance material applications.