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

Vitrimers are a special class of polymer networks that behave like conventional thermosets at service temperatures yet can rearrange their internal topology when heated. Unlike thermoplastics, which simply melt, vitrimers exchange covalent bonds in a controlled, associative manner, so the material flows and reforms without losing its network integrity. This bond-exchange capability is what enables self-healing and reprocessing. Chemists have exploited a variety of dynamic bonds for this purpose, including disulfide exchange, transesterification, imine formation, boronic esters and vinylogous urethanes. The Japanese team focused on vinylogous urethane bonds, which form when acetoacetate groups react with primary amines and can exchange through transamination reactions with free amino groups still present in the network.

The researchers assembled their vitrimers from four largely bio-based building blocks. Polyglycerol polyglycidyl ether, a multi-functional epoxy resin with a bio-based content above 99 percent, served as the crosslinking backbone. Glycerol tris(acetoacetate), synthesized by reacting glycerol with tert-butyl acetoacetate at 135 degrees Celsius for 24 hours, provided the acetoacetate groups needed for vinylogous urethane formation. Cystamine, a disulfide-containing diamine, introduced the second dynamic bond type, while dimer diamine, a flexible fatty-acid-derived diamine supplied by Cargill, acted as a soft, renewable co-monomer. By varying the molar ratio of cystamine to dimer diamine across four formulations, designated VUE-C/D-0/4 through VUE-C/D-3/1, the team could systematically tune the balance between stiffness, flexibility and dynamic bond content.

Characterization confirmed that the intended chemistry had taken place. Fourier-transform infrared spectroscopy showed the acetoacetate carbonyl bands weakening dramatically after curing, while new absorptions characteristic of vinylogous urethane bonds appeared at 1649 and 1604 reciprocal centimeters, alongside a broad hydroxyl stretch from the epoxy-amine reaction. Chloroform extraction experiments yielded gel fractions exceeding 91 percent for all films, evidence of well-formed crosslinked networks. The cured products emerged as transparent brown films with biomass contents of approximately 81 weight percent, a remarkably high figure for epoxy thermosets and a substantial improvement over earlier vinylogous urethane vitrimers that relied on petroleum-based polyamines.

Thermal and mechanical measurements revealed how the cystamine-to-dimer-diamine ratio shaped the final materials. Glass transition temperatures, measured by differential scanning calorimetry, ranged from 10 to 32 degrees Celsius and rose steadily as more cystamine replaced the flexible dimer diamine. Tensile modulus and strength followed the same trend, because the shorter, more rigid cystamine segments stiffened the network. Interestingly, the apparent crosslinking density derived from dynamic mechanical analysis moved in the opposite direction, decreasing with increasing cystamine content. The researchers attribute this counterintuitive result to residual primary amino groups and network heterogeneity, which complicate the interpretation of rubbery-state modulus measurements and show that glass-transition behavior cannot be explained by crosslink density alone.

The most striking results came from stress relaxation experiments, which probe how quickly the network can rearrange its topology. Tested at temperatures from 100 to 140 degrees Celsius, the dual-dynamic formulation VUE-C/D-1/3 relaxed far faster than a control material, VUE-H/D-1/3, in which cystamine was replaced by hexamethylene diamine so that only vinylogous urethane bonds remained. At 140 degrees Celsius, the dual-dynamic vitrimer reached its characteristic relaxation time in just 111.5 seconds, compared with 375.5 seconds for the control. Arrhenius analysis showed the dual-dynamic material had a higher activation energy of 71.1 kilojoules per mole versus 41.9 for the control, meaning its relaxation accelerated more steeply with temperature, a signature of two cooperative exchange mechanisms at work.

Self-healing tests translated this faster relaxation into concrete performance. Rectangular specimens were cut in half, pressed back together and hot-pressed at 140 degrees Celsius for three hours under a modest 0.5 megapascals of pressure. Every formulation healed successfully, with all healed samples strong enough to support a 200-gram load, and each film could be healed at least three times in succession. The dual-dynamic VUE-C/D-1/3 achieved the highest first-cycle healing efficiency, recovering 86 percent of its original tensile strength, while the single-dynamic control managed only 63 percent. Healing efficiencies declined over successive cycles for all films, and within the cystamine series the 1/3 ratio outperformed both 2/2 and 3/1, indicating that beyond an optimal composition the added network stiffness outweighs the benefit of more dynamic bonds.

The study also honestly documents the limits of the technology. When the researchers attempted bulk reprocessing by hot-pressing fragmented samples at 160 or 180 degrees Celsius under 30 megapascals, the pieces fused together but never formed homogeneous, flat specimens suitable for mechanical testing, and the recovered maximum stresses fell below 15 percent of the original values. Infrared spectra revealed that the vinylogous urethane carbon-carbon double bond band at 1604 reciprocal centimeters nearly vanished during this harsh treatment, showing that the dynamic chemistry itself had been chemically altered. By contrast, the same band remained intact after the gentler self-healing conditions, demonstrating that the network can heal under mild conditions that preserve its structure, even if full-scale recycling remains out of reach for now.

The implications reach well beyond one laboratory formulation. Epoxy thermosets are ubiquitous in coatings, adhesives, electronics and composites, and their inability to be repaired or recycled generates enormous waste. By showing that pairing vinylogous urethane and disulfide bonds measurably accelerates network rearrangement and boosts healing efficiency in a network that is roughly 81 percent biomass by weight, the Chiba Institute of Technology team has provided a clear design principle for the next generation of sustainable thermosets. The work also cautions that more dynamic bonds are not automatically better, since stiffness, residual amine content and network heterogeneity all conspire to determine real-world performance. As the field of bio-based vitrimers matures, studies like this one, which carefully isolate the contribution of each dynamic bond type, will be essential guides for engineers seeking materials that are simultaneously strong, renewable and, quite literally, able to heal themselves.

Subject of Research: Self-healing bio-based epoxy vitrimers with dual dynamic vinylogous urethane and disulfide bonds

Article Title: Self-healing bio-based epoxy vitrimers containing dual dynamic vinylogous urethane and disulfide bonds

Article References: Takeda, R., Sugane, K., & Shibata, M. (2026). Self-healing bio-based epoxy vitrimers containing dual dynamic vinylogous urethane and disulfide bonds. Polymer Bulletin, 83(12), Article 661. https://doi.org/10.1007/s00289-026-06726-6

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06726-6

Keywords: bio-based epoxy, vitrimer, self-healing, vinylogous urethane, disulfide bonds, dynamic covalent bonds, stress relaxation, renewable polymers, glycerol tris(acetoacetate), cystamine, dimer diamine, reprocessability