The new material, christened ISSATE for Isosorbide-Succinic anhydride-Tetra epoxy, begins its life as isosorbide, a rigid bicyclic sugar alcohol produced industrially from starch, and succinic anhydride, a bio-based chemical readily obtained from furan derivatives. In a three-step synthetic route, the researchers first reacted the two hydroxyl groups of isosorbide with succinic anhydride at 120 degrees Celsius without any solvent, yielding a diacid intermediate in 87 percent yield. This intermediate was then coupled with an allyl-functional trimethylolpropane derivative using a carbodiimide-mediated esterification, and finally the four pendant allyl groups were converted into epoxide rings through oxidation with meta-chloroperoxybenzoic acid. The result is a colorless, viscous liquid bearing four epoxy groups arranged around the rigid isosorbide core, a molecular architecture that no previously reported isosorbide-based diepoxide has matched.

The tetrafunctional design is the heart of the innovation. Where DGEBA carries only two reactive epoxide ends, ISSATE presents four, dramatically increasing the density of reactive sites available for crosslinking. When cured, this higher functionality translates into a tighter, more densely connected polymer network. At the same time, the succinic linkages threaded through the molecule act as flexible spacers, softening what would otherwise be an excessively brittle structure. The calculated biomass resource carbon content of the resin itself stands at 36.8 percent, and when combined with its curing agent in a complete formulation, the bio-based carbon fraction climbs to approximately 50 percent, compared with a mere 19.2 percent for the conventional DGEBA formulation it was benchmarked against.

Crucially, the researchers did not stop at a bio-based resin; they also chose a bio-based hardener. The curing agent, 1,8-p-menthanediamine or MTDA, is derived from turpentine sourced from pine gum and pine wood. Mixing the resin and hardener in stoichiometric proportions, degassing, and curing through a staged thermal schedule of 80, 120, and finally 160 degrees Celsius produced a rigid, high-performance thermoset. Fourier-transform infrared spectroscopy confirmed the chemistry: the characteristic epoxide peak near 910 wavenumbers nearly vanished after curing, while a new secondary hydroxyl band emerged, the unmistakable signature of the epoxy-amine reaction. A faint residual epoxide signal remained, which the team attributes to the 85 percent purity of the MTDA mixture of cis and trans isomers rather than to incomplete network formation.

One of the most practically significant findings concerns processability. At room temperature, ISSATE flows at a viscosity of 3175 centipoise, substantially lower than the 4763 centipoise measured for DGEBA. Lower viscosity matters enormously in industrial settings, where resins must wet fibers in composite manufacturing, fill intricate molds, and mix uniformly with hardeners without the addition of reactive diluents or solvents. The extended succinic segments appear to be responsible, granting the molecule enough conformational freedom to slide past its neighbors. Differential scanning calorimetry, analyzed with both the Kissinger and Ozawa kinetic methods, revealed a further bonus: the activation energy of the ISSATE-MTDA curing reaction is lower than that of the DGEBA-MTDA system. The researchers attribute this to the tetrafunctional structure providing more reactive sites, the enhanced molecular mobility imparted by the succinic extender, and the improved accessibility of the epoxide groups to the amine hardener, in contrast to the sterically restrictive aromatic backbone of DGEBA.

Mechanical testing told an equally encouraging story. Tensile specimens prepared according to ASTM D638 type V standards showed that the ISSATE-MTDA thermoset achieves a tensile strength of 73.33 megapascals, edging out the 70.67 megapascals recorded for DGEBA-MTDA. More striking still is the elongation at break: the bio-based material stretched 15.68 percent before failing, versus 9.41 percent for the conventional system, a roughly 66 percent improvement in ductility. The stress-strain curve of the ISSATE sample even displays a yield point, a behavior more typical of tough engineering thermoplastics than of brittle epoxy networks. The flexible succinic segments act as built-in tougheners, absorbing deformation energy that would otherwise propagate cracks. Tensile modulus, a measure of stiffness, came in at 892 megapascals for the bio-based system against 911 megapascals for DGEBA, a negligible penalty that keeps the new resin firmly in the realm of structural materials.

Dynamic mechanical analysis added nuance to the picture. The storage modulus of the ISSATE-MTDA network at room temperature and its calculated crosslinking density both marginally exceed those of the DGEBA reference, consistent with its higher functionality. However, the flexible succinic segments cause the storage modulus to decline more rapidly with temperature, and the glass transition temperature of the bio-based thermoset falls below that of its petroleum counterpart. Interestingly, both systems exhibited dual peaks in their damping curves, which the researchers link to the cis and trans configurations of the MTDA hardener. The trans isomer, with its extended molecular shape, creates regions of greater free volume and chain mobility that depress the transition temperature, while the more compact cis isomer contributes to the higher-temperature relaxation. This subtle interplay between hardener stereochemistry and network architecture offers a tunable handle for future formulation design.

Thermal stability, often the Achilles heel of bio-based polymers, proved robust. Thermogravimetric analysis showed that the ISSATE-MTDA system begins to lose mass at 315.42 degrees Celsius, defined at 2 percent weight loss, compared with 332.15 degrees Celsius for DGEBA-MTDA. The slightly earlier onset stems from the ester linkages in the ISSATE backbone, which are inherently more susceptible to thermal cleavage than the aromatic ether bonds of DGEBA. Yet at the 5 percent mass-loss threshold, the bio-based resin still withstands approximately 335 degrees Celsius, comfortably within the high-temperature range expected of serious epoxy thermosets. For adhesives, coatings, and composite matrices that rarely see sustained service above 150 degrees Celsius, this margin is more than adequate, and the trade-off buys sustainability without sacrificing the thermal envelope that matters in practice.

The implications reach well beyond a single laboratory synthesis. Epoxy thermosets are notoriously difficult to recycle because their crosslinked networks resist melting and reshaping, which means that the two million tons produced annually eventually end up in landfills or incinerators. Replacing even a fraction of that volume with resins built from isosorbide, succinic anhydride, and turpentine-derived amines would shift a substantial slice of the thermosetting industry away from fossil carbon and away from bisphenol A, a compound whose endocrine-disrupting reputation has already prompted regulatory restrictions in consumer products worldwide. The Korean team, supported by the Ministry of Trade, Industry, and Energy, frames ISSATE as a promising sustainable alternative to DGEBA-based systems, and the data support that framing: comparable or superior tensile strength, modulus, and elongation, high decomposition temperatures, lower viscosity, faster curing kinetics, and a formulation that is half renewable carbon by composition.

Challenges remain before ISSATE can challenge DGEBA at industrial scale. The multi-step synthesis involves column chromatography purification, a technique that is economical in the laboratory but costly at the ton scale, and the overall yield across three steps must be optimized for commercial viability. The lower glass transition temperature may also disqualify the current formulation from the hottest service environments, such as aerospace primary structures, where DGEBA-based systems with aromatic amine hardeners still reign. Nevertheless, the study demonstrates a principle that resonates across green chemistry: molecular design, not merely feedstock substitution, can close the performance gap between bio-based and petroleum-derived materials. By pairing a tetrafunctional sugar-derived epoxide with a flexible succinic extender and a pine-derived diamine, the researchers have shown that the next generation of epoxies need not ask industry to choose between performance and planetary responsibility. As pressure mounts to decarbonize the chemical sector, resins like ISSATE offer a concrete, measurable path forward, one epoxy group at a time.

Subject of Research: Synthesis and characterization of a tetrafunctional bio-based epoxy resin from isosorbide and succinic anhydride as a sustainable alternative to DGEBA

Article Title: A tetrafunctional bio-based epoxy from isosorbide and succinic anhydride: synthesis, properties and DGEBA comparison

Article References: Toan, M., Kwon, K., & Shin, S. (2025). A tetrafunctional bio-based epoxy from isosorbide and succinic anhydride: synthesis, properties and DGEBA comparison. Advances in Industrial and Engineering Chemistry, 1(1), Article 5. https://doi.org/10.1007/s44405-025-00006-z

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00006-z

Keywords: bio-based epoxy resin, isosorbide, succinic anhydride, DGEBA, tetrafunctional epoxy, thermoset, 1,8-p-menthanediamine, renewable polymers, mechanical properties, thermal stability, curing kinetics, sustainable materials