DESIGN OF PERFLUORINATED AMINOMACROLIGANDS FOR THE IMPLEMENTATION OF ATOM TRANSFER RADICAL POLYMERIZATION IN SUPERCRITICAL CARBON DIOXIDE

摘要

In the 1990's, an explosion of the researches on radical polymerization has been observed in the academic laboratories since the discovery of controlled processes, namely the Nitroxide Mediated Polymerization (NMP), the Reversible Addition-Fragmentation chain Transfer (RAFT) and Atom Transfer Radical Polymerization (ATRP). In each process, the control of the polymerization relies on an equilibrium between active and dormant species. This equilibrium being shifted toward the formation of the dormant species, the radical concentration in the polymerization medium decreases, that favors the propagation step compared to the termination reaction. This characteristic makes the synthesis of polymers with well defined molecular weight, architecture and chain-end functionality easy. Nowadays, because of environmental regulations, green processes are imposing themselves in chemistry, material science and industry. In the past decades, extensive researches have been devoted to the use of supercritical carbon dioxide (scCO_2) as reaction medium in the field of chemistry. Compared to others supercritical fluids, scCO_2 exhibits many advantages as low critical parameters (p_c = 73.8 bar, T_c = 31.1°C), low cost, non toxicity, non flammability and easy recyclability. In the field of polymer synthesis, others factors make scCO_2 an attractive medium. Indeed, CO_2 is easily available in high purity on an industrial scale and, more importantly, CO_2 is relatively inert, except towards anionic species, thus eliminating chain transfer to the solvent as side reaction, and the low viscosity of scCO_2 removes issues of Tromsdorf effect and autoacceleration. As a consequence, scCO_2 is an ideal alternative solvent for polymers to be prepared by free-radical polymerization, cationic polymerization, condensation polymerization, oxidative coupling, transition metal catalysis and in some cases coordination-insertion polymerization. Until recently, conventional free radical polymerization has been extensively studied since it was discovered that amorphous or low crystalline fluoropolymers and silicones exhibit high solubility at easily accessible temperature (＜ 100°C) and pressure (＜ 350 bar) in scCO_2. This observation opened up news areas of research in this medium, mainly in homogeneous as well as in dispersion, suspension and emulsion free radical polymerizations. Nevertheless, only limited attention was paid to the development of controlled radical polymerization, and especially Atom Transfer Radical Polymerization (ATRP).