Functionalized bio-polyesters by nitroxide radical coupling

The preparation of functionalized bio-polyesters by radical grafting of functional molecules is a controversial issue. The well known approach of functionalizing polyolefins, which is the peroxide-initiated melt grafting of maleic anhydride, has been described as a method to improve miscibility and thereby thermal and mechanical properties of polyester blends and composites. Nonetheless, the covalent grafting of functional moieties on polyester chains has not been fully characterized. The major difficulties encountered are due to the inability of IR spectroscopy to differentiate the C=O stretching signals of covalent grafted moieties with those of the polyester chains. In addition, data are not available about the control of chain degradation and crosslinking side reactions during the functionalization process. The radical functionalization of polymers by nitroxyl derivatives is a powerful tool to obtain functionalized materials by keeping under control the side reaction that can affect the process. In fact, nitroxyl free radicals can quickly couple with carbon-centered radical species, such as the macroradicals, and if they are bearing specific functionalities, these can be covalently inserted onto the backbone of a polymer1. For example molecules bearing nitroxides covalently linked to fluorophore moieties (profluorescent nitroxides) have been synthesized and used, as probe of polypropylene degradation2 .Moreover photo-responsive polyolefin were prepared by the simple radical reaction between macroradicals and 4-(1-naphthoate)- 2,2,6,6-tetramethylpiperidine-1-oxyl (NfO-TEMPO)3.