SURFACE MODIFICATION OF POLYOLEFINS THROUGH NITROXIDE-MEDIATED PHOTOGRAFTING

Control and design of surface properties of polymer materials play an important role in expanding their range of employment and defining their applications. A limited change in the physico-chemical characteristics of a solid surface has, in fact, many advantages including (1) improvement of the surface properties of a material without affecting its bulk properties; (2) elimination of the need to redesign the bulk material to achieve a target surface performance; and (3) reduction of costs since all necessary chemistry is confined to the outer layer1. To modify the polymer surface, several methods have been described such as flame treatment2, plasma and corona treatment among the others3. Such surface modification techniques are difficult to control, and often cause problems regarding uniformity and reproducibility combined with another disadvantage that is they require a short time between treatment and application of the coating4. An efficient and fast way to modify a polymer surface is based on surface grafting reactions initiated by ultraviolet irradiation5. This technique shows advantages as: fast reaction rate, low cost of processing, simple equipment, easy industrialization and the distribution of the grafted molecules is limited to a shallow region near the surface1. Usually the mechanism of surface photografting implicates the presence of a photoiniator that, after excitation, by absorption in UV light at a specific wavelength, abstracts an hydrogen atom from the substrate, thereby producing a macroradical. This radical site acts as an initiator for polymerization and/or grafting depending on the structure/reactivity of the used functional moiety. In this communication we report the synthesis of 4-(1-naphthoate)-2,2,6,6-tetramethylpiperidine-1-oxyl (NfO-TEMPO) and 2,2,6,6-tetramethylpiperidine-1-oxyl-4-yl 4,4,5,5,6,6,7,7,8,8,9,9-tridecafluorononanoate (Fluo-TEMPO), the photografting of these molecules onto a copolymer of ethylene/1-octene (Et-co-Ot), the characterization of the functionalized samples by ATR-IR, TGA and XPS and the study of surface properties by means of fluorescence emission and contact angle. Furthermore, by considering that the reaction of nitroxides photografting can be shifted towards the radical species with temperature, the polymerization of styrene by a simple thermal activation was studied, with the aim to investigate the possibility to graft polymer chains starting from the activated surface.