Photoassisted oxypolymerization of alkyd resins: Kinetics and mechanisms

A new three-component system for photoassisted oxypolymerization of alkyd resins containing a drier, a photosensitizer and a radical generator was investigated. Polymerization profiles were recorded by real-time infrared spectroscopy for a thin film exposed for 1 h to simulated sunlight radiation. The kinetic results showed that the system follows complex kinetics. Multiple regression analysis was used to model the influence of the drier, the photosensitizer and the radical generator on the final conversion and total polymerization rate during photooxidation. The mechanisms involved were studied through laser spectroscopies. Laser flash photolysis was used to measure the rate constants of reaction between the radicals formed from the photodissociation of the radical generator and the model compounds of alkyd resins, leading to the rapid formation of hydroperoxides. The photosensitizer was expected to produce singlet state molecular oxygen that reacts on the alkyd resin, and time-resolved chemiluminescence technique was used to determine the quenching rate constant of singlet oxygen by model compounds. On the basis of these results, a mechanism for the photoassisted oxypolymerization of alkyd resins is proposed that account for the all the different reaction pathways.

► The photoassisted oxypolymerization of alkyd resins was studied by RT-FTIR.
► The effet of Cobalt salt, radical generator and photosensitizer was demonstrated.
► The specific role of BAPO and Rose Bengal on alkyd resin drying was pointed out.
► The radical reactivity toward alkyd resins model compounds are characterized.
► The singlet oxygen reactivity toward alkyd resins model compound was measured.