Lewis acid ionic liquid catalysed synthesis of bioderived surfactants from β-pinene

Abstract

Cationic polymerisation of β-pinene (βP) via earth abundant catalysis has been investigated as a route to low molar mass poly(β-pinene) (PBP) for surfactant applications. As a ‘greener’ alternative to the often hazardous and poorly abundant Lewis acid catalysts reported for the cationic polymerisation of βP, imidazolium-based Lewis acid ionic liquids have been used as catalysts for the polymerisation, yielding polymers of up to M_n = 2560 g mol⁻¹. Iron(III) chloride (FeCl₃) proved to be an effective catalyst for the transformation in a scaled-up, industrially applicable polymerisation resulting in polymers of slightly higher molar mass (M_n = 5680 g mol⁻¹). Supercritical carbon dioxide (scCO₂) proved to be an effective solvent for the purification of the polymers on a large scale, efficiently removing unreacted monomer and solvent. The unsaturated nature of the polymer has been exploited via post-polymerisation functionalisation reactions (epoxidation/hydrolysis and radical thiol–ene), endowing the polymers with hydrophilic groups. The functionalised PBPs were fully characterised, demonstrating variations in thermal properties compared to the unfunctionalised polymer. Finally, with careful balancing of the amphiphilicity, the functionalised polymers were shown to stabilise oil/water emulsions for up to two weeks, demonstrating the potential of these bioderived materials in several surfactant applications.