From the Design of Novel Tri- and Tetra-Epoxidized Ionic Liquid Monomers to the End-of-Life of Multifunctional Degradable Epoxy Thermosets

Abstract

The design and development of multifunctional epoxy thermosets have recently stimulated continuous research on new degradable epoxy monomers. Herein, tri-and tetra-epoxidized imidazolium monomers were rationally designed with cleavable ester groups and synthesized on a multigram scale (up to 100 g), yielding room-temperature ionic liquids. These monomers were used as molecular building blocks and cured with three primary amine hardeners having different reactivities, leading to six different network architectures. Overall, the resulting epoxy−amine networks exhibit high thermal stability (>350 °C), excellent mechanical properties combined with a shape memory behavior, glass transition temperatures (T g s) from 55 to 120 °C, and complete degradability under mild conditions. In addition, nonpolarizable, all-atom molecular dynamics simulations were applied in order to investigate the molecular interactions during the polyaddition reaction-based polymerization and then to predict the thermomechanical and mechanical properties of the resulting networks. Thus, this work employs computational chemistry, organic synthesis, and material science to develop high-performance as well as environmentally friendly networks to meet the requirements of the circular economy.

Theoretical Analysis of Physical and Chemical CO2 Absorption by Tri- and Tetraepoxidized Imidazolium Ionic Liquids

“…The CL&Pol forcefield has previously been shown to accurately simulate experimental properties such as density for base anions and cations used in this study, thus making it ideal to use as a base forcefield to apply. , From the applied forcefield, the density values found by our fundamental and theoretical investigation corroborate the magnitude of density experimentally obtained for a library of imidazolium-based IL monomers, including the tri- and tetra-epoxy monomers bearing the anion NTf 2 – instead of Cl – . − In the current contribution, the densities predicted were 1.24 and 1.28 mg/mL for tri- and tetra-epoxy monomers. Similarly, our co-workers found 1.25 ∓ 0.05 mg/mL and 1.33 ∓ 0.06 mg mL –1 for the identical backbone monomers bearing NTF 2 – as a counterion instead of Cl – …”

“…Similarly, our co-workers found 1.25 ∓ 0.05 mg/mL and 1.33 ∓ 0.06 mg mL −1 for the identical backbone monomers bearing NTF 2 − as a counterion instead of Cl − . 28 When producing radial distribution functions (RDFs) with TRAVIS, the center of mass (COM) was used for all groups. Coordination numbers were calculated using these RDFs and taking the integral until the first minima, signaling the end of the first solvation shell.…”

“…This methodology was shown to be sufficient for convergence of diffusion coefficients in analogous IL systems using the same forcefield and converging the mean-squared displacement, as shown in the Supporting Information. − System were constructed containing 500 of each component (epoxyimidazolium cation, Cl anion, and CO 2 ; the epoxyimidazolium cations being shown in Figure ). Water was not included in the system due to prior experimental characterization studies on epoxy-ILs indicating that water impurities are below 1% for both the tri- and tetra-exoxy imidazolium monomers, being 0.6 and 0.2% respectively . The temperature used for simulations was 300 K, controlled with a Nosé–Hoover thermostat.…”

“…Water was not included in the system due to prior experimental characterization studies on epoxy-ILs indicating that water impurities are below 1% for both the tri-and tetra-exoxy imidazolium monomers, being 0.6 and 0.2% respectively. 28 The temperature used for simulations was 300 K, controlled with a Nose−Hoover thermostat.…”

“…New ILs including epoxy groups as a sidechain in imidazolium cations have been previously investigated as monomers for epoxy–amine polyaddition, leading to (multi)­functional-dedicated polymers. , To further increase the thermal stability and mechanical performances and to obtain networks with higher glass transition temperatures, additional epoxy groups were incorporated in tri- and tetraepoxidized imidazolium bistriflimide (NTf 2 ) ILs being synthesized and used for polymerization . These additional epoxy sites were shown to be thermodynamically accessible for polymerization reactions with steric hindrance not significantly reducing reactivity.…”