CHAPTER 11: Solubility and Synthesis of Polymers Using Supercritical Carbon Dioxide

In this chapter, the authors attempt to illustrate the utilisation of supercritical carbon dioxide (scCO₂) as a suitable alternative to conventional organic solvents in numerous different synthetic polymerisation processes by giving an overview of recent literature in this area. There are a host of opportunities in polymer science as a result of the unique characteristics associated with scCO₂. The use of this solvent leads to the generation of polymeric products possessing well-defined structures (particles with well-defined morphologies) and properties. The literature has shown the versatility of scCO₂, with its successful implementation in a variety of different polymerisation processes including step-growth polymerisation, chain-growth homogeneous polymerisation, precipitation polymerisation, dispersion polymerisation, suspension polymerisation and emulsion polymerisation. It is a particularly attractive medium for precipitation and dispersion polymerisations due to the insolubility of numerous high molecular weight polymers in scCO₂. It has been shown that scCO₂ is ideal for conducting heterogeneous controlled living radical polymerisation (CLRP) since the monomer, control reagents and initiator are completely soluble in scCO₂ but the resultant polymer is not and precipitates out. This results in the polymer only being able to continue to grow in the particle phase, leading to a living polymer having a microstructure that is controlled and well-defined.