The antioxidant behavior of functional nitroxide grafted polyethylene samples

In this work, the thermo- and photo-oxidation stability of functional nitroxide grafted polyethylene (PE) samples was tested. TEMPO derivatives bearing hydroxyl, benzoyl, 1-naphthoyl, and a hindered phenol group as substituents were covalently grafted on the polymer chains by nitroxide radical coupling (NRC) reaction carried out in the melt using a peroxide as a radical initiator. The method enabled polymer crosslinking to be limited and the number of grafted groups to be tuned. The antioxidant behavior of the dual-functionalized PE samples (the alkoxyamine group in quasi-equilibrium with the nitroxide radical, and the functional group attached to the 4-position of the TEMPO ring) was evaluated determining the oxidation induction time (OIT) via DSC measurements and monitoring the carbonyl index via FT-IR before and after thermal and UV aging. The results evidenced only a partial resistance towards the photo-oxidation, whereas the samples functionalized with the hindered phenol substituted TEMPO showed improved thermal oxidation stability.