The Next Generation of Recyclable Epoxy-anhydride Networks Combining Metallic Ionic Liquid (MIL) and Epoxidized IL-Based Monomers

According to the political and ethical demands of our times, scholars and industries are pushed to search for sustainable solutions, i.e., to design recyclable, reusable, or degradable materials. The challenge is to go beyond conventional epoxy networks based on visphenol A diglycidyl ether (DGEBA), which firstly contain bisphenol A (BPA) and secondly cannot be recycled. Here, a generation of recyclable epoxy thermosets was designed and developed for the first time from the copolymerization between tri- and tetra-IL based monomers containing cleavable bonds with conventional anhydride (MTHPA) with our without the presence of a metallic ionic liquid (MIL). Thus, the influence of these monomers and the MIL on the curing kinetics, the epoxy conversion, and the physical properties of the resulting networks was assessed. In particular, the combination of the two has proved to be a powerful tool to tailor the architecture–physical property relationships of the resulting IL-modified epoxy networks and to produce recyclable networks. As a consequence, the glass transition temperature T_g of the networks ranged from 60 to 140 °C, while the mechanical performances varied from 2.5 to 3.5 GPa, combined with a thermal stability up to 330 °C. Then, the epoxy networks were subjected to physical recycling (a solvent-free method, i.e., hot-pressed process) and a chemical recycling process using dissolution in ethylene glycol and repolymerization at 150 °C. Finally, all the epoxy networks showed their ability to be recycled, which was highly dependent on the network architecture.