Synthesis and properties of some aromatic polyamides with coumarin chromophores

A novel monomer diacid, 6,6′-methylenebis{2-oxo-8-{2-[(2-oxo-2H-chromen-7-yl)oxy]acetoxy}-2H-chromene-3-carboxylic acid}, having two substituents (2-oxo-2H-chromen-7-yl)oxyacetate in the aromatic moiety, was synthesized and used in a direct polycondensation reaction with various aromatic diamines using triphenyl phosphite and pyridine as condensing agents to give a series of new aromatic polyamides with photosensitive coumarin pendent groups. Polyamide properties were investigated by DSC, TGA, GPC (gel permeation chromatographic analysis), and wide-angle X-ray scattering, viscosity and solubility measurements. The introduction of bulky side chains in the structure of aromatic polyamides led to moderate inherent viscosity values (0.40-0.87 dLg−1) and increased solubility of these polymers in aprotic polar solvents such as NMP (N-methylpyrrolidone), DMAc, DMSO and DMF, and in less polar solvents like Py and THF. The good solubility of these polyamides was in agreement with their amorphous character as evidenced by X-ray diffraction diagrams. Gel permeation chromatography evidenced high molecular weights (49,400-63,900 gmol−1) which allowed transparent, flexible and tough films to be cast from polymer solutions. These aromatic copolyamides showed good thermal properties associated with glass transition temperatures (Tg) in the range of 221-257 °C and the onset of decomposition in air above 390 °C. UV illumination (λ > 300 nm) of the polymer films induced crosslinking between polyamide molecules through a [2π + 2π] photocycloaddition at the CC bond of coumarin moieties. Information concerning the photoreactive property of coumarin-containing polymers was obtained by studying the changes in the UV absorption spectra and IR spectra of irradiated polymeric films.