Novel Epoxy-Amine Vitrimers with Built-in Catalytic Functionality

Vitrimers uniquely merge the desirable attributes of thermosets, such as high mechanical strength and dimensional stability, with thermoplastic features such as repairability, reprocessability, and recyclability. This combination arises from associative dynamic bond-exchange reactions. Consequently, vitrimers represent an attractive materials platform for lowering resource consumption and waste generation, both central objectives of a circular economy.

Here, epoxy-amine vitrimers are introduced that can be processed, repaired, and recycled without sacrificing thermomechanical performance. During curing, tertiary amines formed in situ function as internal transesterification catalysts, avoiding the use of external catalysts that may plasticize the network or leach over time. By adjusting diamine structures, the network properties were tuned to obtain materials with T_onset up to 260 °C, T_g up to 145 °C, characteristic relaxation times (τ*) of about 15–20 min at 180 °C, and storage modulus E′ up to 2 GPa.

The optimal formulation formed a liquid precursor that cured readily at ambient conditions. This composition was further investigated as a feedstock for material-extrusion additive manufacturing (MEX). To adjust viscosity for printing, two silica fillers (fumed silica and PDMS-modified silica) were incorporated. Increasing silica loading from 5 to 15 wt% raised viscosity by three orders of magnitude and produced beneficial shear-thinning behavior suitable for MEX processing. Consequently, diverse complex geometries (bars, honeycombs, dog-bone specimens, and dice) were printed with high resolution, excellent dimensional accuracy (<2%), strong interlayer adhesion, and minimal shrinkage (<2%).

This research was supported by the Luxembourg National Research Fund (FNR) through the SusPoCo (PRIDE21/16748260) project.