Catalyst-Free Epoxy Vitrimers Based on Transesterification Internally Activated by an α–CF₃ Group

TLDR

Vitrimers are polymer networks that undergo associative exchange reactions, enabling reprocessability, and recent catalyst‑free variants avoid leaching, aging, and sintering while maintaining properties after repeated reshaping. The study reports a catalyst‑free epoxy vitrimer incorporating α‑CF3‑substituted ester groups. A tetra‑acid precursor was synthesized via a catalyst‑free thia‑Michael addition, then ring‑opening polymerized with DGEBA or BDGE to form ester‑linked networks, whose curing was monitored by rheology, DSC, and FTIR, and the α‑CF3 group’s accelerating effect on transesterification was demonstrated by stress‑relaxation experiments and computational modeling. The vitrimer exhibited over 70 % gel content after 24 h in THF, retained mechanical and thermal properties after 2 h reprocessing at 150 °C, and confirmed fluorinated groups as potent internal activators for transesterification vitrimers.

Abstract

Vitrimers are polymer networks in which associative exchange reactions can take place under specific conditions, thus conferring reprocessability to insoluble materials. Recently, catalyst-free vitrimers have emerged as a new generation of vitrimers able to overcome potential leaching, aging, and sintering issues of catalysts and to ensure the preservation of vitrimer properties after numerous reshaping processes. Here, a catalyst-free epoxy vitrimer featuring α-CF3-substituted ester functions is reported. First, a new tetra-acid precursor was synthesized via a catalyst-free thia-Michael addition. A catalyst-free ring-opening polymerization was then performed on two different diepoxy monomers (DGEBA and BDGE) to obtain polymer networks composed of ester linkages. Curing was evaluated by rheology, differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR) monitoring of the polymerization kinetics. A gel content of over 70% was measured after 24 h in tetrahydrofuran (THF). Finally, the accelerating effect of the α-CF3 group on transesterification reactions was highlighted by stress-relaxation experiments and analyzed computationally on a molecular model system. Reprocessability tests were carried out at 150 °C for 2 h. The mechanical and thermal properties of the reshaped materials were similar to those of the initial ones. This study demonstrates the potential of fluorinated groups as powerful internal activators for transesterification vitrimers.