Synthesis and Characterization of Homogeneous Epoxy Networks: Development of a Sustainable Material Platform Using Epoxy-Alcohol Polyaddition

Abstract

Over the last decades, increasing industrial and scientific research focused on sustainable alternatives to replace petroleum-based epoxy resins. Next to the predicted scarcity of fossil resources, evermore social emphasis is shifted towards the environmental impact of such materials, as crosslinked petro-based polymers bear a large carbon footprint and are inherently non-recyclable or (bio)degradable. While thermal curing of epoxy monomers with polyfunctional amines and anhydrides has been intensively discussed, surprisingly, their polymerization behavior using alcohols as co-curing agents in a step-growth mechanism and the mechanical properties of the resulting materials is scarcely described in literature. Therefore, we developed a novel polyaddition system of epoxy and alcohol monomers with a high content on renewable carbon. The polymerization mode of bio-based epoxides with alcohols using imidazoles as catalysts was studied via 1H-NMR analysis, revealing a controlled alternating co-polymerization between difunctional epoxy and alcohol monomers. Furthermore, we were able to determine the theoretical heat of polymerization (100-120 kJ mol−1) for the polyaddition of di- and trifunctional monomers via differential scanning calorimetry. Additionally, a long-term stability study demonstrated desirable pot-life of the formulations of up to 28 days. By varying the core structure (aliphatic, alicyclic, aromatic) and functionality (di-, trifunctional) of the epoxy monomers, high-performance thermosets with a tunable TG (0−110 °C) and high tensile toughness of up to 18 MJ m−3 were obtained while simultaneously achieving high monomer conversions (over 90%). Finally, analysis of the network homogeneity revealed the formation of homogeneous and regulated epoxy-based polyadducts from sustainable resources that could enable the replacement of state-of-the-art petrochemical-derived epoxy resins.