Reaction calorimetry in supercritical fluids : a study of the dispersion polymerization of methyl methacrylate in supercritical carbon dioxide

This thesis is devoted to the study of the dispersion polymerization of methyl methacrylate in supercritical carbon dioxide (scCO2), using a poly(dimethylsiloxane) macromonomer (PDMS macromonomer) as stabilizer. Supercritical fluids (SCF) and SCF mixtures are characterized by a temperature and a pressure above their critical point(s), which is the last point on the vaporization line of a pure component. This means that these fluids operate from moderate to high pressure. They can be used in various processes ranging from extractions, nanoparticle formation for controlled drug release, chemical reactions and polymer processing. Nowadays, the best candidate for SCF processing is carbon dioxide. The fundamental motivation of using scCO2 as a solvent is based on its potential to replace harmful chemical organic volatile compounds (VOCs) in order to develop more sustainable and environmentally friendly chemical processes. At this point, the crucial role of CO2 in the development of the so-called "green chemistry" comes on the stage. CO2 is a natural abundant compound with low toxicity exhibiting no inflammability. This last property is very advantageous considering the cost investments spent by the chemical industry to control the safety of the chemical processes using highly flammable compounds like VOC solvents. As expected, environmental arguments are not sufficient to motivate the development of new chemical process routes. Therefore, additional arguments to use SCFs have to be found, and they do exist. As supercritical fluids are compressible fluids they can exhibit liquid-like and gas-like properties, which can be tuned easily by varying the operating conditions, like pressure and temperature. This fundamental behavior of SCF is their main asset and demonstrates their superiority to develop more flexible processes. The polymer industry is one of the industries that uses the largest volumes of organic solvents and sometimes halogenated ones, well known to destroy the ozone layer. The use of scCO2 gives to chemists and engineers the opportunity to develop more sustainable polymer processes, considering the numerous chemical and physical advantages of carbon dioxide. The processing of scCO2 for polymer production is no more than fifteen years-old. This means that a certain quantity of knowledge has been acquired but still a lot of unknowns hinder their promotion at industrial level. This work is inserted in this context and finds there its main motivations. This thesis is composed of two different but intrinsically connected approaches of the dispersion polymerization of the methyl methacrylate (MMA) in scCO2. A part of this thesis is devoted to the development of techniques allowing the on-line monitoring of polymerizations in scCO2 at "larger" scale, conducted from an engineering approach. The intrinsically connected part is devoted to the understanding of the fundamental phenomena that govern the dispersion polymerization of MMA in scCO2, its ki