FUNCTIONALIZED POLYMERS BY NITROXIDE RADICAL COUPLING REACTION

Design and preparation of functionalized polymeric materials bearing covalently linked functional moieties, such as chromophores, stabilizers, drugs, etc, has drawn great interest in recent years. Functionalized polymers can be prepared by polymerization or by post-polymerization reactions. Direct polymerization often required to use protected monomers and specific polymerization techniques and can be rather expensive. Differently, post-polymerization modification is an attractive approach to extend the applications and convert commodity plastics into products with new, desirable and tunable properties. Among the post-polymerization modification methods, the nitroxide radical coupling (NRC) reaction is a very interesting tool to graft specific functionalities onto polymer chains. It also provides excellent control of macroradical formation versus grafting of functional molecules thus limiting the radical-induced crosslinking/branching and degradation and retaining structural properties of parent material. This talk discusses examples of preparation and covalent grafting of functional nitroxide derivatives (RO-TEMPO) on polyolefins and biodegrable aliphatic polyesters. Emphasis is given to evidence the functional properties of modified materials. A profluorescent nitroxide was used to obtain fluorescent polymers with a complete transfer of the optical properties of the chromophore to the polymer matrix. Azo-aromatic TEMPO derivatives able to isomerize under UV irradiation were also successfully synthesized and bond to polyolefins. It was found that the isomerization process of modified polymers can be controlled by modulating the irradiation wavelength and that the isomerization kinetics depend on the mobility of both chromophore and polymer chains. Moreover, the surface of these materials showed a change in the wettability after isomerization. Macroalkoxy amines bearing a hindered phenol unit inducing an antioxidant response were also prepared by NRC reaction. In this case the functionalized polymers showed a remarkable improvement of both thermal and photo-oxidation stability and migration test demonstrated that the oxidative stability is mostly retained under leaching conditions