The compounds at the heart of the study are far from laboratory curiosities. Lactones serve as feedstocks for biodegradable plastics and polyurethanes, while epoxides are essential building blocks for adhesives, coatings, and the epoxy resins found throughout electronic materials. Both classes of molecules are also widely used as intermediates in pharmaceutical and fine-chemical manufacturing. Any improvement in how they are made therefore resonates well beyond academic chemistry, pointing toward safer and more sustainable industrial processes that rely less on hazardous reagents and harsh conditions.

Organic electrosynthesis uses electricity to drive the formation of organic compounds, and it has attracted growing interest as a greener alternative to conventional synthesis because it can reduce the quantities of chemical oxidizing and reducing agents that traditional routes require. Yet, as Ryu’s team notes, most previous studies have concentrated on bulk-solution variables: the applied voltage, the choice of electrode materials, and the electrolyte composition. The microscopic environment immediately surrounding the electrode, the place where molecules actually exchange electrons and undergo transformation, has received comparatively little attention. The new study argues that this neglect has been a costly oversight, because the electrode surface is precisely where chemistry can depart most dramatically from what the bulk solution suggests.

The physical reason is straightforward but consequential. When protons, or hydrogen ions, are generated or consumed at an electrode faster than they can be transported away through the solution, the local pH can diverge sharply from the pH measured in the bulk liquid. The team found that this divergence affects not only the generation of the reactive oxygen species needed for the reaction, but also the reactivity of the organic molecules themselves and the stability of the products once formed. To gauge how widespread the phenomenon might be, the researchers analyzed more than 600 papers published since 2010 and found that in approximately 89 percent of the studies examined, the reaction at at least one electrode involved the transfer of protons as well as electrons. That figure suggests local acidity shifts are not a quirk of a few specialized reactions but a variable that should be considered across the entire field of organic electrosynthesis.

Electrochemical measurements made the scale of the divergence vivid. Even when the bulk solution was nominally neutral, the environment near the cathode was estimated to turn alkaline at around pH 11, while the region near the anode became acidic at roughly pH 2.5. Under such extreme local conditions, the supply of reactive oxygen species required for the reaction can fall, the chemical form of the starting material can change, and degradation of the desired product can accelerate. This explains why simply adjusting the pH of the bulk solution is not enough: the microscopic environment where the reaction actually takes place must be engineered as well.

To put the principle to work, the researchers chose the Baeyer–Villiger oxidation as a representative transformation. This classic organic oxidation inserts an oxygen atom into a ketone, converting it into an ester or a lactone, and lactones in particular are cyclic esters used in materials such as biodegradable plastics and polyurethanes. Conventional Baeyer–Villiger chemistry typically depends on highly reactive oxidants such as peroxyacids, which create challenges in reagent handling and byproduct disposal. Instead of adding such oxidants externally, the team established an electrochemical pathway in which oxygen gas is activated at the electrode and an oxygen atom is transferred directly to the organic molecule. Isotope-tracing experiments confirmed that the oxygen atom incorporated into the final product originated from oxygen gas rather than from water, a crucial mechanistic verification.

The team also uncovered an elegant cooperation between the two electrodes. Reactive oxygen species generated by oxygen reduction at the cathode initiate the oxygen-transfer reaction, while the hydrogen peroxide produced along the way is recycled back into reactive oxygen species at the anode. The two electrodes therefore do not perform entirely separate roles; they work in tandem to maintain the supply of reactive species the reaction demands. The researchers confirmed that this process is highly sensitive to local pH, which gave them a mechanistic basis for controlling acidity near the electrodes rather than merely observing it.

Combining computer simulations with electrochemical measurements, the team mapped how local pH changes under different operating conditions and then designed a reactor to exploit that understanding. The design narrows the distance between the electrodes and allows the electrolyte to flow between them, so that the acidic environment near the anode and the alkaline environment near the cathode can counterbalance one another, damping out the extreme deviations that otherwise sabotage the chemistry. The quantitative payoff was striking. Compared with conditions in which local pH deviations were not mitigated, the proportion of target product formed selectively rose from approximately 16 percent to approximately 97 percent. Production per unit time climbed steadily with electrolyte flow rate, showing an approximately 14-fold difference between the lowest and highest flow rates tested. Shrinking the electrode gap from 20 millimeters to 4 millimeters boosted the production rate by about 2.2-fold. Most tellingly, when the solution was not allowed to flow at all, almost none of the target product formed, even though the voltage and solution composition were identical, proof that reaction success can hinge on the local environment as much as on electrode material or applied potential.

Under the optimized conditions, the researchers synthesized lactones from 18 different ketone compounds, obtaining the representative product ε-caprolactone at an 82 percent yield. ε-Caprolactone is the feedstock for polycaprolactone, a biodegradable polymer used in medical materials including surgical sutures and drug-delivery systems. The same local pH control principle was then extended to epoxide synthesis, yielding products from six alkene substrates, which demonstrates the breadth of the approach across feedstocks used in adhesives, coatings, and resins for electronic materials. Notably, the entire process runs at room temperature and atmospheric pressure, eliminating the need for separate heating or pressurization equipment, and because electricity is the energy source, the approach could in principle be coupled with electricity generated from renewable sources in future chemical plants.

The industrial implications are considerable. Pharmaceutical and fine-chemical intermediates, which carry high added value and demand careful safety management, align well with the advantages of electrochemical processes: reduced reliance on hazardous oxidants and the ability to operate with relatively compact equipment. The authors caution, however, that further process optimization and validation at production scale will be required before commercial application. The broader significance of the study lies in reframing the discipline itself, shifting organic electrosynthesis beyond the optimization of voltage and solution composition toward what the researchers describe as designing the environment in which molecules actually react. Professor Ryu, who supervised the research, said the study transforms local pH near the electrode from a hidden variable into a controllable design principle, adding that to improve the efficiency of organic electrosynthesis, scientists need to design not only the reaction substrates and catalysts but also the environment in which the molecules actually react. Seonghyeon Min and Junghoon Lee, M.S. students in the department, participated as co-first authors, with integrated M.S./Ph.D. student Hanju Kim as co-author, and the team plans to extend the local-environment approach to a wide range of electrochemical reactions and processes. The research was supported by Seoul National University, the National Research Foundation of Korea, and the Institute for Basic Science.

Subject of Research: Local pH control in organic electrosynthesis for producing lactone and epoxide chemical feedstocks

Article Title: Producing plastic feedstocks with oxygen and electricity: SNU professor Jaeyune Ryu’s team uncovers a ‘hidden variable’ in organic electrosynthesis

Article References: Producing plastic feedstocks with oxygen and electricity: SNU professor Jaeyune Ryu’s team uncovers a ‘hidden variable’ in organic electrosynthesis. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: organic electrosynthesis, local pH, electrochemistry, Baeyer-Villiger oxidation, lactones, epoxides, epsilon-caprolactone, reactor design, reactive oxygen species, sustainable chemistry, Seoul National University, plastic feedstocks

The study, led by Watcharee Funfuenha and Wanich Limwanich of Rajamangala University of Technology Lanna, together with colleagues at Chiang Mai University, centered on a deceptively simple idea. Instead of using liquid titanium(IV) n-butoxide directly as an initiator, the researchers first allowed it to ring-open ε-caprolactone at 130 degrees Celsius with no solvent present, producing short living PCL chains that remain capped with reactive titanium-oxygen active centers. Three versions of these macroinitiators, dubbed TiCL2, TiCL4, and TiCL8, were prepared using 2, 4, and 8 mole percent of the titanium alkoxide respectively. Because the concentration of titanium determines how many chains grow from each metal center, the chain length and molecular weight of the macroinitiators increased as the titanium content decreased, giving the team a tunable family of initiators with precisely controlled architectures.

What distinguishes these materials from conventional initiators is that they are not merely catalysts but genuine macromolecular species, carrying living poly(ε-caprolactone) segments that can themselves seed further polymerization. The concept echoes earlier work with tin(II) macroinitiators, but titanium offers a compelling advantage: titanium compounds are generally regarded as low-toxicity and environmentally benign compared with organotin species, which have faced increasing regulatory scrutiny. By pre-forming the titanium-PCL adduct, the researchers create a species in which the reactive Ti-O bond sits at the end of an organic chain, ideally positioned to coordinate incoming monomer and insert it into the growing polymer, the classic coordination-insertion mechanism that underpins much of modern lactone polymerization chemistry.

To understand exactly how these macroinitiators behave, the team turned to differential scanning calorimetry, a technique more familiar for measuring melting points than for probing reaction kinetics. By monitoring the heat released as the polymerization proceeds under controlled heating rates of 4, 6, 8, and 10 degrees Celsius per minute, they were able, for the first time, to extract non-isothermal kinetic parameters for ε-caprolactone polymerization initiated by titanium macroinitiators. The approach follows recommendations from the ICTAC Kinetics Committee, the international body that sets standards for thermal analysis, lending rigor to the analysis. Intriguingly, only the most titanium-rich variant, TiCL8, proved effective at promoting the ring-opening polymerization under these dynamic heating conditions, suggesting that a minimum density of active centers is required for the reaction to proceed at an appreciable rate.

From the calorimetry data, the researchers applied the Kissinger-Akahira-Sunose isoconversional method, a well-established approach for extracting activation energies from experiments conducted at multiple heating rates. The results revealed a clear concentration dependence: the activation energy fell from 73.5 plus or minus 2.9 kilojoules per mole at 10 weight percent TiCL8 to 64.8 plus or minus 1.1 kilojoules per mole at 20 weight percent. In practical terms, a lower activation energy means the reaction proceeds more readily, requiring less thermal pushing to get over the energetic barrier. The frequency factor, determined by fitting an n-order reaction model to the data, followed the same trend, confirming that higher macroinitiator loadings genuinely accelerate the polymerization rather than merely shifting it within the experimental window.

The team went further, computing the activation enthalpy and activation entropy of the process through Eyring-type transition state analysis. At higher TiCL8 concentrations, the transition state formation was facilitated, but the activation entropy became more negative, indicating a more ordered activated complex. This is chemically intuitive: when many titanium centers coordinate monomer molecules simultaneously, the arrangement demands a greater degree of molecular organization than a sparse distribution of active sites would require. Together with a proposed coordination-insertion mechanism, in which the monomer coordinates to the titanium center before inserting into the Ti-O bond, these thermodynamic parameters paint a coherent picture of a reaction whose speed and efficiency can be dialed simply by adjusting the initiator architecture and loading.

Kinetics on a small scale, however, only matters if the chemistry survives scale-up. To test this, the researchers performed larger-scale polymerizations under the same solvent-free conditions using conventional heating. The outcome was striking: high molecular weight PCL was obtained from all three macroinitiators, with weight-average molecular weights reaching 7.18 by ten to the fourth, 7.81 by ten to the fourth, and 6.88 by ten to the fourth grams per mole for TiCL2, TiCL4, and TiCL8 respectively. Molecular weight in this range corresponds to robust, mechanically useful material suitable for film blowing, melt processing, and biomedical fabrication. Achieving it without any solvent not only eliminates a major source of waste and cost but also simplifies purification, since no residual reaction medium needs to be stripped from the product.

The green credentials of the process were then pushed further with microwave irradiation, an energy-transfer method that heats reaction mixtures volumetrically rather than through the vessel walls. Microwave-assisted polymerization sharply reduced reaction times and, crucially, rescued the performance of the less reactive macroinitiators. Under microwave conditions, TiCL2 and TiCL4, which had lagged behind in conventional runs, delivered PCL with weight-average molecular weights of 6.08 by ten to the fourth and 6.23 by ten to the fourth grams per mole respectively. This suggests that the energy profile of microwave heating preferentially benefits systems with fewer, less accessible active centers, potentially by promoting faster and more uniform activation of the Ti-O bonds. For manufacturers weighing energy costs against product quality, the ability to reach high molecular weights quickly at moderate power inputs could prove decisive.

The broader significance of the work lies in its convergence of several green chemistry principles into a single, practical platform. The monomer, ε-caprolactone, derives from a ring-strained cyclic ester that polymerizes without releasing small molecules, making the process atom-economical. The initiator is based on titanium, an abundant and comparatively harmless metal. The reaction proceeds in bulk, with no solvent, at a moderate 130 degrees Celsius, and can be accelerated further by microwave energy rather than prolonged heating. Each of these choices independently reduces the environmental footprint of PCL production; combined, they point toward a manufacturing route that could compete with conventional processes on cost while outperforming them on sustainability metrics.

There remain challenges ahead. The concentration dependence of the kinetics means that process designers must carefully balance initiator loading against molecular weight targets, since the macroinitiator chain length and the density of active centers pull in opposite directions. Understanding how residual titanium content affects the properties and biocompatibility of the final polymer will also be essential for medical applications. Nevertheless, by coupling rigorous non-isothermal kinetic analysis with demonstration-scale synthesis, the Thai team has provided exactly the kind of quantitative foundation that translates laboratory chemistry into industrial practice. As demand for biodegradable polyesters continues to climb amid global pressure on plastic waste, solvent-free titanium-catalyzed routes to PCL may well move from the pages of Polymer Bulletin into the factories of the circular economy.

Subject of Research: Solvent-free ring-opening polymerization of ε-caprolactone using titanium(IV) macroinitiators to produce biodegradable polycaprolactone

Article Title: Development of new titanium(IV)-macroinitiators towards the green and facile ring-opening polymerization of ε-caprolactone

Article References: Funfuenha, W., Cheechana, N., Meepowpan, P., Punyodom, W., & Limwanich, W. (2026). Development of new titanium(IV)-macroinitiators towards the green and facile ring-opening polymerization of ε-caprolactone. Polymer Bulletin, 83(12), Article 645. https://doi.org/10.1007/s00289-026-06707-9

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06707-9

Keywords: polycaprolactone, ring-opening polymerization, titanium(IV) macroinitiator, epsilon-caprolactone, biodegradable polyester, solvent-free synthesis, microwave-assisted polymerization, DSC kinetics, coordination-insertion mechanism, green chemistry, activation energy, polymer bulletin