Infrared analysis of the photochemical behaviour of segmented polyurethanes .1. Aliphatic poly(ester-urethane)

The photochemical behaviour of aliphatic-based poly(ester-urethanes) is investigated. Polymer samples are submitted to irradiation in the presence of oxygen in conditions of long wavelength irradiation (lambda > 300 nm) or short wavelength irradiation (lambda = 254 nm). The evolution of the structure of photooxidized polymers is monitored by FTi.r. analysis of thin samples and the different photoproducts formed are identified. It is shown that long wavelength irradiations provoke an induced oxidation of urethane functions. This reaction is initiated by hydrogen atom abstraction on the methylene groups in the alpha position of nitrogen atoms. On irradiation at short wavelength, the results provide evidence for a dual mechanism for photooxidation: induced oxidation and direct photolysis of the urethane groups following three possible photoscissions that involve the homolysis of C-N and C-O bonds. (C) 1997 Elsevier Science Ltd.