Synthesis and properties of some aromatic polyamides with coumarin chromophores

A novel monomer diacid, 6,6′-methylenebis{2-oxo-8-{2-[(2-oxo-2 H-chromen-7-yl)oxy]acetoxy}-2 H-chromene-3-carboxylic acid}, having two substituents (2-oxo-2 H-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 [2 π + 2 π] photocycloaddition at the C C 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.