Synthesis and Properties of Diels–Alder-Based Covalent Adaptable Networks from CO2 and 1,3-Butadiene Derived Polyesters

Abstract

α-Ethylidene-δ-vinyl-δ-valerolactone (EVL), a trifunctional monomer derived from CO₂ and 1,3-butadiene, provides a versatile platform for the construction of functional polyesters. A furan-functionalized monomer (EVL-FML), synthesized via thiol–Michael addition of EVL, exhibits a low ceiling temperature (T_c = −102.4°C) that precludes its homopolymerization. To overcome this thermodynamic limitation, EVL-FML is copolymerized with the Michael adduct of EVL and 1-propanethiol (EVL-SPr), which possesses a higher T_c of −2.4°C. Catalyzed by 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD), the ring-opening copolymerization (ROCP) yields polyesters bearing furan groups (PF-x, 0–50 mol%) with number-average molecular weights up to 13.1 kg mol⁻¹, and narrow distributions (Р< 1.2). Kinetic studies reveal that the ROCP follows pseudo-first-order kinetics, with a reaction order of 0.37 with respect to TBD. The reactivity ratios are determined to be r_EVL-SPr = 0.94 and r_EVL-FML = 0.75. Subsequently, maleimide-functionalized (13–59 mol%) polyesters (PM-y) are prepared via post-polymerization modification of PEVL-SPr. Thermally reversible covalent adaptable networks (CANs) are constructed through the Diels–Alder reaction between PF-x and PM-y, exhibiting cross-link densities ranging from 110 to 572 mol m⁻³ and tensile strengths between 0.42 and 12.45 MPa. These networks demonstrate excellent self-healing, reprocessability, and inherent degradability, offering a promising pathway toward sustainable functional materials.