Deep eutectic solvents for Cu-catalysed ARGET ATRP under an air atmosphere: A sustainable and efficient route to poly(methyl methacrylate) using a recyclable Cu(ii) metal-organic framework

Abstract

Atom Transfer Radical Polymerisation (ATRP) is one of the most important techniques to synthesize well-defined polymers with predetermined molecular weight, designed microstructure and tailor-made functionalities. Although ATRP has been extensively studied in a variety of common Volatile Organic Solvents (VOCs) and water, there is significantly less work done using fashionable and environmentally friendly Deep Eutectic Solvents (DESs). Aiming to develop greener ATRP routes by allowing the recycling of the employed transition metal catalyst, we herein present the homogeneous and heterogeneous Cu-catalysed ARGET variation of the ATRP processes using methyl methacrylate (MMA) as the model monomer and a DES as a green solvent. The homogeneous ARGET ATRP was performed employing CuCl2 as a catalyst and FDA-approved tin(ii) 2-ethylhexanoate [Sn(EH)2] as a reducing ARGET agent, under an air atmosphere. The polymerisations proceeded in a controlled/"living" fashion according to reversible deactivation radical polymerisation (RDRP) standards. Heterogeneous ARGET ATRP was carried out by using a DES-insoluble Cu(ii) Metal-Organic Framework (MOF) as a recyclable catalyst in the absence of organic ligands, employing Sn(EH)2 as a reducing agent, under an air atmosphere. Under these experimental conditions, well-defined poly(methyl methacrylate) (PMMA) was obtained (Đ ≈ 1.2) under controlled RDRP conditions. Importantly, both the MOF catalyst and DES were successfully recycled up to 6 consecutive catalytic cycles to synthesize PMMAs with comparable macromolecular features and yields.