Industrial application of supercritical carbon dioxide soluble polymers

Carbon capture has become a major global process, carbon dioxide (CO2) can be separated as a by-product in the industrial production of ammonia and ethanol using different methods such as cryogenic separation or the use of membranes, reducing the carbon footprint of the process. Our aim is to make positive use of the captured carbon dioxide as an alternative green solvent for polymer synthesis. Dispersion polymerisation is an industrially relevant technique that provides polymer particles with defined morphology and size that are used in various applications from drug delivery to electronics. However, the main limitation for using supercritical carbon dioxide (scCO2) as solvent in this technique is the lack of highly soluble, environmentally friendly and affordable stabilisers. In this thesis the synthesis of hydrocarbon based stabilisers for dispersion polymerisation is explored. Until very recently, only fluorocarbon and silicone based (polydimethylsiloxane, PDMS) polymers showed any significant solubility in scCO2 but these are expensive and not environmentally friendly. Hydrocarbon stabilisers such as poly(vinyl acetate-stat-vinyl pivalate) (P(VAc-stat-VPi)) constitute a viable alternative. However they have only worked successfully for one monomer, N-vinyl pyrrolidone (NVP). The application of P(VAc-stat-VPi) based stabilisers in dispersion polymerisation of methyl methacrylate (MMA) is thus explored in this work. A range of P(VAc-stat-VPi)-block-PNVP block copolymers with different molar masses and compositions were synthesised using controlled radical polymerisation (RAFT/MADIX) and characterised by different techniques such as nuclear magnetic resonance (NMR) spectroscopy and size exclusion chromatography (SEC) showing narrow dispersities. Solubility of the stabilisers was tested using a variable volume view cell. Block copolymers of different DP of PNVP were tested in dispersion polymerisation of MMA. Although none of the reactions proceeded to high conversion as expected for this kind of process, micron sized polymer particles of spherical morphology could be observed by scanning electron microscopy (SEM) for some of the stabiliser materials, making them a very promising alternative