Effect of ultraviolet radiation on vinyl ester network based on bisphenol A
A vinyl ester resin (VER) based on bisphenol A (BA) was synthesized starting from a commercial epoxy resin (Ropoxid 501) and acrylic acid (AA). The synthesized VER was transformed into a vinyl ester network (VEN) in the presence of benzoyl peroxide. The behavior of VEN on UV radiation (λ > 300 nm), up to 200 h exposure time, was investigated using surface gloss measurements, differential scanning calorimetry (DSC), optical microscopy (OM), Fourier transform-infrared spectroscopy (FT-IR), UV–vis spectroscopy and weight loss. The UV radiation produces important modifications of VEN sample. Both the gloss index variation and OM micrographs show the presence of the roughnesses on the surface of VEN film. The decrease of the glass transition temperature with an increase of the irradiation time indicates the scission of the VEN chains under UV action. FT-IR and UV–vis spectroscopy evidence the presence of the photo-oxidative degradation products (hydroxyl and carbonyl groups, peroxides and hydroperoxides). The unstable hydroperoxides decompose by producing radicals that may attack the VEN chains. A possible mechanism of VEN photo-oxidative degradation was suggested.
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 194, Issues 2–3, 20 February 2008, Pages 275–282