Heavy-Metal-Free Epoxy Vitrimers Enhanced with Liquid Crystalline Phase

A new, heavy-metal-catalyst-free epoxy vitrimer system modified with a liquid crystalline epoxy resin (LCER) is presented. A critical innovation in this work was the replacement of conventional toxic transesterification catalysts, such as zinc compounds, with an excess of a bio-based compound: glycerol. Two anhydrides, maleic anhydride (MA) and phthalic anhydride (PA), were evaluated as curing agents to determine their impact on the thermal and self-healing properties of the resulting networks. The study revealed that the systems cured with an aliphatic anhydride exhibited superior self-healing characteristics compared to their aromatic counterparts. Moreover, the use of MA allowed for a lower curing temperature. Differential scanning calorimetry (DSC) was employed to analyze the thermal behavior of the resin and its compatibility with the epoxy vitrimer network, as well as the curing process itself and the thermal characteristics of the obtained polymer network. Hot-stage-polarized optical microscopy (HS-POM) was used to confirm the formation of liquid crystalline phases of the LCER and to track the healing process. Furthermore, it was observed that in selected formulations, the addition of LCER itself was sufficient to induce self-healing capabilities without the necessity of adding multi-hydroxyl alcohol.