Vitrimers are a class of polymer networks featuring dynamic covalent crosslinks that can undergo associative bond exchange. These dynamic polymer networks hold a notable promise as recyclable thermosets with self-healing capabilities, provided by network rearrangements at the molecular level, allowing for macroscopic flow. When the relaxation time is sufficiently short, vitrimer material behaves like a thermoplastic even though it is covalently crosslinked. However, temperature-induced malleability remains limited by the high-viscous nature of vitrimers. Therefore, the present article explores the cure dependence of structural relaxation and vitrimer transition phenomena of a dynamic disulfide-containing epoxy vitrimer. Stress relaxation measurements reveal that intermediate cure states—accompanied by lower crosslinking density—exhibit bond exchange and segmental relaxation rates exceeding those of fully cured networks over an order of magnitude. This enhanced dynamics facilitates lower viscosities and residual times during high-temperature malleability processing. Advanced methods combining rheology, cure kinetics, and thermomechanical analysis are utilized to assess the cure dependence of the vitrimer transition temperature (Formula presented.). We outline a distinct cure dependence of (Formula presented.), which may be approximated by a linear correlation, suggesting that viscoelastic flow can be initiated at significantly lower temperatures in undercured networks. These findings provide valuable guidance for enhancing material and processes, contributing to opening doors to the “melt processing” of this family of materials.

The present article introduces a high-performance epoxy vitrimer to target structural composite applications. By utilizing a reactive diluent derived from biobased feedstock, the maximum glass transition is tailored to maintain a sufficient temperature window for reprocessing, avoiding the degradation of permanent bonds. Different fractions of permanent cross-links are imbued into the network structure, and the hybrid network is elucidated by creep and stress relaxation. The creep behavior at service temperatures below 150 °C remains unaffected, while slower bond exchange dynamics and higher extrapolated topology freezing temperatures T_v are reported for an increasing number of permanent cross-links. Comprehensive studies of physicochemical, thermo-rheological, and curing reactions are carried out and summarized in a conversion-temperature phase diagram first reported for a vitrimer. The vitrimers show great malleability, even with permanent cross-link fractions above the theoretical limit for a percolated network formation, and we demonstrate recycling by comminuting and subsequent reconsolidation. These findings provide valuable guidance for enhancing material and process development of high-performance vitrimer resins and lay the groundwork for advancing composites built on vitrimer matrix systems.

The development of epoxy resin formulations from renewable feedstocks has been thoroughly explored in the chemical literature. A simple one-pot chemical reaction involving sustainable phenolic molecules and epichlorohydrin results in the production of renewable epoxy monomers. These monomers can be cured with amines or anhydrides to yield cross-linked thermosetting resins. Although a wide variety of recipes exist, there is a notable gap in the application of these sustainable resin formulations to engineering contexts. This gap is primarily due to the lack of comprehensive, standardized analyses of these resin recipes, which impede their potential use in advanced composite applications. In this study, we reveal a high-performance resin formulation utilizing epoxidized phloroglucinol derived from brown algae in combination with an aerospace-grade amine hardener. The resin processing and thermomechanical properties are investigated using ASTM standard tests including tensile strength, flexural strength, fracture toughness, and interlaminar shear strength. Given the detailed comparative analysis, the partially renewable resin recipe outperforms petroleum derived analogues.

The present study describes the development of cure kinetics and chemo-rheological models for an epoxy vitrimer based on polyimine exchange to elucidate the potential in terms of processing and accurate process selection. Reaction kinetics is investigated using differential scanning calorimetry. A good agreement between the model and data can be demonstrated for different stoichiometries by selecting a parallel reaction approach consisting of an nth-order and an autocatalytic approach. The suggested chemo-rheological model captures the intrinsically high viscosity of the resin over a broad temperature and curing range, even after the gelation point. The Di-Benedetto equation represents the glass transition temperature advancement with cure while combining the rheological Winter-Chambon criterion and the kinetic model determines the degree of cure at the gelation. These results give important advice for improved process modeling of vitrimeric resins, facilitate accurate process selection, and pave the way towards the development of composites based on the matrix system investigated in this work.