The study of the photooxidation mechanism of crosslinked polyesters used for flat steel coating can be based on the analysis of photoproducts at the molecular scale: these photoproducts are formed in the matrix under exposure in an accelerated photoageing chamber SEPAP 12–24. Hydroxy functionalized aliphatic polyesters crosslinked with highly methoxy methylated melamines or aliphatic blocked polyisocyanates have been examined. The different photoproducts involved in the oxidative evolution have been identified using FTIR spectroscopy and chemical derivatization treatments. Physical changes have been examined by DMTA analysis on free polymer films. Mechanisms accounting for the photooxidation of each crosslinked system was proposed, involving both chain oxidation and crosslink scissions. Crosslinking due to radical recombinations have been shown to occur in the oxidized matrix.

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