Photochemical transformation of diketone dopants in polyester matrices: Effect of dopants concentration and polyester structure on changes in molecular characteristics and hydrolysis of the matrices

Photochemical transformations of photoactive diketone derivatives, 1,2-diphenylethane-1,2-dione (benzil, BZ) and 1,4-bis(benzoylcarbonyl)benzene (bisbenzil, BIS), and the effects of their transformations on changes in the molecular characteristics and hydrolytic properties of poly(ε-caprolactone) (PCL) and polylactide (PLA) matrices are reported. Studies were performed in a broad dopant concentration range of 0.2–7.5 wt%. Structural changes were observed by FTIR spectroscopy. FTIR spectroscopy proved the progressive transformation of BZ to benzoyl peroxides and, in the case of PCL, the formation of polar groups. Changes in molecular characteristics were observed in GPC traces. Irradiation of the doped polymer films at λ > 400 nm under an air atmosphere resulted mainly in the degradation of the polymer matrices. Additionally, high dopant concentrations in PCL led to partially crosslinked structures with gel contents up to 15%. The photochemical transformation of dopants had a large impact on the PCL matrices compared to that of the PLA matrices. A subsequent hydrolysis process was investigated by determining the extractable products as well as using GPC. Hydrolysis of irradiated PCL samples showed a significant acceleration of hydrolysis compared to that of nonirradiated samples. Furthermore, the hydrolysis rate gradually increased with increasing dopant concentration. The PCL crosslinking and degradation is adjustable by the type of dopant, concentration of dopant and intensity of light during irradiation of PCL. In contrast, a photochemical pretreatment had no observable effect on the hydrolysis of PLA under the investigated conditions.