Molecular, Macromolecular and Nanostructured Antioxidants

During the past decades, the key role of Reactive Oxygen Species (ROS) in different pathologies has been indicated to take part to many physiological and pathological processes including aging, cancer, neurodegenerative and cardiovascular diseases. The role of ROS is not delimited inside living organisms, but affects also synthetic polymers limiting their commercial use. Indeed, common polymers like polyolefins are subjected to deterioration by oxygen-promoted oxidative processes both during processing and end-use conditions. In biological systems the detrimental action of free radicals is continuously balanced by the action of specific enzymes and dietary antioxidants able in transforming ROS in non-oxidant species. The oxidative degradation of polymers is generally prevented or retarded by adding low concentration (0.05-0.5 wt%) of antioxidants, such as hindered phenols or amines and organo-phosphorous compounds. However, when pro-oxidant species overwhelm antioxidant defenses, oxidative stress and oxidative degradation take place in biological systems and polymers, respectively. The research of new antioxidants with an improved efficacy respect to the already used is then very important and was the central topic of this PhD thesis. In Chapter 1 the oxidation phenomena and the most important antioxidants, both natural and synthetic ones, are briefly introduced. In Chapter 2 is reported our work concerning the preparation and evaluation of the antioxidant activity of 7-hydroxy dihydrobenzo[b]thiopenes and 7-hydroxy benzo[b]thiophenes developed by both the structure of Vitamin E and that of sulfur containing antioxidants previously synthesized by our research group. Part of this work was published in the journal Organic Letters (Organic Lett. 2016, 18, 5464-5467). In Chapter 3 is described the use of polymeric antioxidants, obtained from the copolymerization of a polymerizable antioxidant with appropriate monomers, as better stabilizing additives (respect to low molecular weight molecular antioxidants) for polyolefins. This work was also published on the Polymer Degradation and Stability journal (Polym. Degrad. Stab. 2017, 144, 167-175). In the same chapter it is also reported the synthesis of new antioxidant derivatives suitable for the preparation of polymeric antioxidants through copolymerization reactions or reactive blending. The stabilization of polyolefins is also the subject of Chapter 4, where are reported the outcomes of my work in the research group of professor S. Al-Malaika at the Aston University, Birmingham (UK), that was focused on the direct linking of a phenolic antioxidant on polyethylene trough grafting reactions. Finally, in Chapter 5 is described the modification of commercially available molecular antioxidants (Trolox, Catechin and BHT) for the preparation of metallic nanostructured antioxidants (Au, γ-Fe2O3, Co) in order to reduce their toxicity in biomedical applications, for the treatment of stress related pathologies and as additives for ether solvents stabilization.