POLYMER SURFACE MODIFICATION BY PHOTO-GRAFTING OF FUNCTIONAL NITROXIDES

The modification of polymer surfaces by UV-induced graft polymerization is a powerful method to change the surface characteristics of a polymer without altering its bulk features [1]. In this work an alternative approach to modify the surface properties of an ethylene-octene copolymer (EOC) and of a polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) block copolymer is described. X-TEMPO derivatives were used as functional species in place of unsaturated monomers. Indeed TEMPO radicals can react with macroradicals by coupling giving rise to the functionalization of polymers in a peroxide-initiated radical process [2, 3]. In an UV photo-grafting process, the excited photo-initiator gives rise to macroradicals by H-abstraction from the polymer chains, and the X-TEMPO derivatives react with the carbon-centered macroradicals by coupling leading to the surface functionalization of the polymer material (Fig. 1). The 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (BzO-TEMPO), the 4-(1-naphthoate)-2,2,6,6-tetramethylpiperidine-1-oxyl (NfO-TEMPO) and the 4-(4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluoro-nonanoate)-2,2,6,6-tetramethyl-piperidine-1-oxyl (Fluo-TEMPO) were used as functional X-TEMPO radicals, whereas the 4-methoxybenzophenone (MeOBP) was used as a photo-initiator. The resulting functionalized polymers were characterized by ATR-FTIR spectroscopy, Electron Paramagnetic Resonance (EPR) and thermogravimetric analysis (TGA). Data confirmed the grafting of X-TEMPO derivatives and allowed the evaluation of the amount of grafted species. The fluorescence emission spectroscopy was used to investigate the optical properties of the NfO-TEMPO functionalized samples, while the contact angle measurements highlighted the wettability of the polymer surface modified with Fluo-TEMPO. Results show that the properties of the free X-TEMPO derivatives were transferred to the polymer surface thus giving "functional" polymer films.