Epoxy Vitrimer Materials by Lipase-Catalyzed Network Formation and Exchange Reactions

Abstract

The preparation and reprocessing of an epoxy vitrimer material is performed in a fully biocatalyzed process wherein network formation and exchange reactions are promoted by a lipase enzyme. Binary phase diagrams are introduced to select suitable diacid/diepoxide monomer compositions overcoming the limitations (phase separation/sedimentation) imposed by curing temperature inferior than 100 °C, to protect the enzyme. The ability of lipase TL, embedded in the chemical network, to catalyze efficiently exchange reactions (transesterification) is demonstrated by combining multiple stress relaxation experiments at 70−100 °C and complete recovery of mechanical strength after several reprocessing assays (up to 3 times). Complete stress relaxation ability disappears after heating at 150 °C, due to enzyme denaturation. Transesterification vitrimers thus designed are complementary to those involving classical catalysis (e.g., using the organocatalyst triazabicyclodecene) for which complete stress relaxation is possible only at high temperature.

An effective approach for the preparation of epoxy vitrimers by in situ formation of dynamic and permanent linkages in a one-pot curing reaction

“…This result might indicate uneven curing of the X_MA-Pae-8 network arising from the two-step reactions (amine/epoxy and ketene/–OH addition reactions). 38 The heterogeneous curing network could be improved by the preparation of the crosslinked resin in a one-step curing process, and this was supported by the one tan δ peak found with X_MAMA/BE188-V (Fig. 2(c)).…”

Thermolatent Heterogeneous Epoxy–Acid Formulation for the Manufacture of Preimpregnated Sheets and Composites with Vitrimer Properties

“…At 25 °C, its mixture with PPGEF shows the carbonyl vibration in ATR. Effective dissolution at 25 °C induces a drop in viscosity, detrimental to prepregs’ manipulation (Figure S4), and the epoxy–acid system is known to be reactive at 100 °C once dissolved …”

“…Effective dissolution at 25 °C induces a drop in viscosity, detrimental to prepregs' manipulation (Figure S4), and the epoxy−acid system is known to be reactive at 100 °C once dissolved. 43 However, heterogeneous formulations bring challenges in obtaining homogeneous samples: fast curing at high temperatures led to samples with bubbles and a high quantity of unreacted CHDA crystals. Meanwhile, with a temperature too low, the slow curing unfavorably allows time for sedimentation of CHDA at the bottom of the samples.…”

Time–Temperature Superposition of Polybutadiene Vitrimers

“…As a consequence, the network maintains connectivity and constant cross-link density, thereby preventing the dissolution of polymer in a good solvent at all temperatures below backbone degradation conditions. At the same time, however, cross-link exchange enables the network topology to fluctuate and the material to flow. − This combination of solvent resistance and processability makes vitrimers not only appealing for improving plastic sustainability and high-performance applications, − but also as a platform for investigating how dynamic cross-links impact the physics of the underlying polymer chains.…”