Solvent processable and recyclable covalent adaptable organogels based on dynamic trans-esterification chemistry: separation of toluene from azeotropic mixtures

Abstract

New covalent adaptable networks (CANs) possessing processability and recyclability to monomers are desirable as an alternative to traditional plastics to address plastic waste-related issues. Moreover, conventional polymeric networks are generally insoluble in organic solvents. Herein, we report a set of CANs that can be dissolved in alcoholic solvents via reactive depolymerization and fully recycled to monomers. In this study, we have utilized trans-esterification of α-substituted β,β′-diesters with multi-hydroxy compounds under moderate temperature conditions (110–140 °C) to develop a set of polyester-based CANs. The synthesized CANs showed ultimate tensile strength (UTS) and elongation at break values up to ∼1.1 MPa and ∼595%, respectively. These CANs showed thermal stability up to 215 °C. The films were stable under acidic and basic conditions. These CANs readily depolymerized and dissolved in an alcoholic solvent at ∼120 °C within 15 h via competitive trans-esterification with the solvent. The films re-formed on evaporation of the solvent followed by curing at 140 °C. The reprocessed CANs exhibited UTS (∼1.0 MPa) and Young's modulus (∼1.8 MPa) values comparable to the original samples. Due to their simple synthesis, solvent processability, recyclability, economically reliable starting materials and moderate processing temperature, these polyester CANs may be suitable for various commercial applications. The CANs swiftly and selectively absorbed aromatic compounds compared to other organic solvents and swelled by ∼750 wt% in toluene within 90 min. These properties were utilized to efficiently separate aromatics from various azeotropic mixtures involving toluene, methanol and water.