Photoaging of polyoctenamer: Influence of the initial microstructure

The photooxidation of two polyoctenamers with different initial microstructures has been investigated through irradiation at lambda > 300 nm at 35 degreesC. Chemical changes were detected using conventional techniques based on FTIR spectroscopy and specific chemical titration. In parallel, the physical evolution was monitored using viscoelastic experiments with the aim of establishing the relationship between chemical and physical changes. Our finding is that the initial microstructure influences the stoichiometric ratio of oxidative byproducts. Moreover, dynamic oscillatory measurements underline an evolution of the molecular structure of the materials from the start of the UV exposure, involving rapid cross-linking. Whereas, at the same time, no chemical change was detected by FTIR spectroscopy. We point out that the physical evolution is independent on the initial microstructure. The critical gel characteristics are quite identical for both samples (gel time t(gel) = 125 min, relaxation exponent n = 0.4).