Photochemical behaviour of semi-aromatic polyamides

Abstract

Semi-aromatic polyamides were irradiated with monochromatic light of short wavelength ( λ = 254 nm) or polychromatic light of long wavelength ( λ > 300 nm), in the presence or the absence of oxygen. The changes of the irradiated samples were characterized by both UV-visible and FTIR spectroscopies. It was observed that in short wavelength irradiation, a direct homolysis of the NHCO bond of the amide function occurred, leading to the formation of the amine and aldehyde. The crotonization of the aldehydes led to unsaturated aldehydes, which were responsible for the reversible discoloration phenomena observed. The long-wavelength irradiation in the presence of oxygen was shown to provoke a photoinduced oxidation of the methylene adjacent to the aromatic ring. The determination of the photooxidation profiles showed that the oxidation was limited to the superficial layers of the samples. The formation of imide groups and thermally unstable N-1 hydroxyl-acid groups was observed. The photooxidation as well as the hydrolysis of imide groups was shown to produce primary aliphatic or aromatic amides and carboxylic acid functions.