The Role of Pressure at the Limit of the Dispersion Stability in the Polymerization of Methyl methacrylate in Supercritical Carbon Dioxide
Sustainable process-product development & green chemistry
SCF as Solvent Substitutes (T1-8)
Keywords: supercritical, calorimetry, MMA, polymerization
The past two decades have seen an unprecedented scientific interest on the application of supercritical fluids as solvents for polymerization reactions. The motivation has been the effort to substitute many of the organic solvents used today, having been classified as volatile organic compounds, by more environmentally friendly substances like supercritical carbon dioxide. Numerous systems have been investigated but the dispersion polymerization of methyl methacrylate is without doubt the one that has attracted the most attention.
In our study we employ the well-established technique of reaction calorimetry to observe the effect of the pressure on the evolution of the polymerization reaction of methyl methacrylate in supercritical carbon dioxide. The heat released during the separate phases of the reaction, e.g. the coagulative nucleation period and the controlled coagulation period, is monitored and quantified. The region where the dispersion is at its limit of formation is also identified. It demonstrates a particulate interest since a step in the reaction acceleration is observed and it is shown how this is strongly connected to the reaction rates of the two formed phases, namely the CO2-rich phase and the polymer-rich phase.
The same analysis leads to the explanation of the pressure evolution during the reaction. It is shown how the difference between the initial and the final pressure switches from positive values to negative ones depending on the initial pressure and its effect on the dispersion stabilization. The pressure evolution is also explained based on the partitioning of the monomer in the two phases and its negative mixing volume with supercritical CO2.
Presented Monday 17, 16:20 to 16:40, in session SCF as Solvent Substitutes (T1-8).
