Carbonatation of [ethylene–glycidyl methacrylate]-based copolymers with carbon dioxide as a reagent: from batch to solvent-free reactive extrusion

Abstract

The carbonatation of semi-crystalline [ethylene–glycidyl methacrylate]-based polymers (Lotader® grades) was achieved using carbon dioxide as a reagent and quaternary ammonium salts as organocatalysts to transform the polymers’ epoxide pendant groups into cyclic carbonate moieties. A batch reactor allowed us to assess the kinetics, dependence on a catalyst and overall potential of this carbonatation. The influence of the ammonium salt composition (anion/cation) was studied in toluene at 110 °C to circumvent the high melting temperatures of these ethylene unit-rich copolymers and obtain a homogeneous medium. The amount of catalyst, CO₂ pressure and temperature were also optimized (TBAB, 5 mol% vs. epoxy content, 4.0 MPa, 110 °C) to allow for quantitative conversion of epoxides into cyclic carbonates. Subsequently, the reaction was transposed, for the 1^st time, to reactive extrusion under CO₂ using a dedicated co-rotating twin-screw extruder to allow for CO₂ containment within the polymer melt. This solvent-free reactive process is perfectly adapted to semi-crystalline and/or high-T_g polymers. After optimization, a yield of up to 78% of cyclic carbonate, in addition to orthogonal epoxide, could be obtained with THAB (7.5 mol% vs. epoxy content, ∼30 g h⁻¹ of cat.) at 150 °C with an industry-compliant polymer flow rate of 2 kg h⁻¹. The respective reactivities of Lotader® grades were compared in batch and in an extruder, unveiling this trend towards carbonatation: AX8840 < AX8700 < AX8900. Sustainability and enhanced productivity of the carbonatation methodology developed herein relies on the use of CO₂ as a C1 reagent for the functionalization of epoxide-bearing polymers harnessing a continuous and clean reactive extrusion process allowing, in a single operation and a few minutes, the production of functional polymers at the kilogram scale under solvent-free conditions.