Applicazione di un anodo sacrificale di Al in eATRP semplificata

Electrochemically mediated ATRP (eATRP), usually performed in a two-compartment cell with Pt. A significant improvement of the traditional setup was achieved by using inexpensive non noble metals as cathode. Also, the two-compartment cell was replaced with an undivided cell with a sacrificial aluminum anode. However, there are still some unclear mechanisms about the effects of metal ions released from the sacrificial anode on catalyst stability and polymerization efficiency. These issues have been addressed in this thesis work and the obtained results will be presented as described below. Chapter I is a review on the long development history of RDRP and simultaneously introduces several CRP methods such as NMP, OMRP, RAFT and ATRP. Chapter II provides a detailed description of the development of eATRP and progresses on the understanding of its dynamics and determination of several important parameters. Subsequently, simplified eATRP (seATRP) is introduced with special emphasis on some unclear issues about the effects of the anodic dissolution of Al on the stability and performance of copper-based catalysts, a subject that was deeply investigated during the PhD thesis and will be fully treated in Chapters IV-VIII. The used reagents, instruments and corresponding principles, and related experimental methods are listed in Chapter III. Chapter IV discusses the influences of Al3+ ions generated from anodic dissolution of Al wire on two widely used ATRP catalysts ([CuIIL]2+, L= TPMA and Me6TREN) in DMF, DMSO, and MeCN. Both voltametric analysis and evolution of UV-vis-NIR spectra proved that TPMA forms more stable complexes with Cu2+ and Cu+ than with Al3+ in DMF and DMSO. But [CuITPMA]+ is destroyed via replacement of Cu+ by Al3+. Conversely, copper complexes coordinated with Me6TREN suffer from a competition in all investigated solvents. The ligand showed higher affinity for Al3+ than for Cu2+ and Cu+. However, addition of enough ligand to form complexes with both Al and Cu ions could effectively suppress the competition and allow maintaining the stability of [CuIIL]2+ in the studied solvents. Investigations on the problem of competition were extended to typical ATRP conditions for n-BA. Chapter V confirmed the results obtained in pure solvents. The negative interference of Al3+ ions during eATRP could be suppressed by adding excess amine ligand. Using a two-fold excess of Br without excess ligand, was found to be beneficial although it could not fully restore the efficiency of the Cu catalysts. Besides organic media, investigations were also carried out in aqueous solutions, as discussed in Chapter VI. In this system, no remarkable changes occurred to [CuIITPMA]2+ stability, while [CuIIMe6TREN]2+ disappeared through exchange of the ligand with Al3+ and reduction of Cu2+ and [CuIIMe6TREN]2+ by active Al. Reduction of Cu2+ to metallic Cu by Al was proved by the UV-vis-NIR spectra of the complexes and SEM-EDX characterization of the Al surface. The competitive equilibria between Cu and Al ions for the ligands were effectively suppressed by adding excess ligand over Cu2+. In Chapter VII, we also took account of the pH effects caused by the formation of aluminum hydroxides during the anodic dissolution process. When more Me6TREN was added to the solution, the initial pH could be restored but not [CuIIMe6TREN]2+; only a small parameters. In Chapter VIII, the possibility of using low-cost Na2CO3 to suppress the competitive equilibria was explored. Addition of Na2CO3 not only could effectively suppress the competitive complexation equilibria in both organic solvents and aqueous media, but was also capable of recovering the pH in aqueous solutions and hence effectively enhance the polymerization rate. The amount of CO32- must be strictly controlled with respect to Al3+ ions, , otherwise, it can combine with [CuIIMe6TREN]2+ to form a new more stable complex [CO3CuIIMe6TREN] with a more negative redox potential.