Exploiting the tuneable density of scCO2 to improve particle size control for dispersion polymerisations in the presence of poly(dimethyl siloxane) stabilisers

The dispersion polymerisation of methyl methacrylate (MMA) is a widely employed method for producing discrete, spherical PMMA particles from traditional solvents, which cover a broad particle size range. With environmental impact becoming an ever more widespread concern, there is increasing demand for greener solvents with advantageous characteristics. Supercritical carbon dioxide (scCO ₂) offers the potential of a greener solvent for dispersion polymerisations, with uniquely tuneable solvent properties and the ability to avoid energy and cost intensive drying steps. In this work, the tuneable density of scCO ₂ was exploited to influence the solubility of poly(dimethyl siloxane) stabilisers in the dispersion polymerisation of methyl methacrylate as a proof-of-concept. By varying the reactor pressure at the start of polymerisation, the final particle size was altered, without the need for cosolvent systems used in traditional solvents. Finally, this additional particle size control mechanism was exploited to achieve a PMMA particle size range far beyond what was previously attainable with this stabiliser. Thus, further enhancing the potential use of scCO ₂ as a green solvent for industrial polymer production.