Traditional polymers such as plastics are widely utilized for their chemical inertness and durability. However, these very properties make them non-degradable in nature and cause long-term environmental damage due to their persistence. In this light, biodegradable polymers that can be broken down by microbes have gained a lot of attention and scientists have turned towards cyclic ketene acetals (CKAs), a group of organic compounds containing carbon atoms and oxygen arranged in a ring-like structure, to develop biodegradable polymers.
CKAs have the remarkable ability to undergo radical ring-opening polymerization (RROP), a chemical process which allows specific organic groups to be introduced into the polymer backbone, and are ideal monomer candidates for designing polyesters with tunable degradation properties. However, the exact influence of CKA monomer structure on the overall polymerization process remains unclear.
To address this gap, a team of researchers, including Assistant Professor Shin-nosuke Nishimura and Professor Tomoyuki Koga, both from the Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, Doshisha University, Japan, has conducted a new study. Their research findings were published online in the journal Macromolecules on August 19, 2025.
Explaining the motivation behind their study, Dr. Nishimura says, “In the field of RROP, the role of monomer asymmetry had remained largely unexplored, despite its potential to unlock new levels of control over polymer microstructure and degradability. I was motivated to address this knowledge gap by combining experimental polymer synthesis with a detailed kinetic model, aiming to bring a new dimension to the structure–reactivity–function relationship in degradable polymer design.
Initially, the research team synthesized a series of 5-membered CKAs containing alkoxymethyl substituents at the 4-position. These novel compounds were then subjected to nuclear magnetic resonance (NMR) spectroscopy to determine their exact chemical structures. Subsequently, the researchers studied one representative monomer called 5a in detail using different chemical conditions and temperatures. NMR spectroscopy revealed that polymers made from 5a contained polyester structures, indicative of their degradability. To further test the degradability of 5a polymers, they conducted OECD 301F testing, a standard biodegradability test, and compared the results to those of cellulose, a common biodegradable polymer. 5a polymers had a degradation rate of 20% compared to a rate of 40% observed in cellulose.
The scientists then shifted their focus to assess the impact of chemical modification of the alkoxymethyl group at the 4-position of CKAs. To this end, they utilized 5a monomer and a non-substituted 5-membered CKA called C5, and modified the concentrations of monomers and temperatures during the polymerization reaction. They found that 5a did not form backbiting structures (unstable chemical structures that affect a polymer’s properties) under high temperatures or varying monomer concentrations.
Finally, they further confirmed the effect of chemical modification of the alkoxymethyl group at the 4-position through NMR spectroscopic analyses of reaction solutions. Ring retention during polymerization can lead to the introduction of inert chemical groups that cannot be cleaved and reduce the overall biodegradability of a polymer. Results showed that 5a CKA had less than 10% of ring-retaining fractions across different chemical conditions.
Inspired by their findings, the research team went a step further and developed a kinetic simulation model using density functional theory (DFT) calculations—a quantum mechanical framework to study the properties of an atomic system. Notably, their kinetic model could verify the results obtained through experimental analysis of 5a and provided insights into the exact mechanisms by which 5a CKAs react during RROP.
Sharing the impact their findings may have, Dr. Nishimura explains, “Our findings may contribute to the development of practical degradable materials such as environmentally friendly packaging that reduces microplastic formation, agricultural mulch films that break down after a defined period, and biomedical materials that degrade safely in the body.”
“In the next 5 to 10 years, our kinetic model could serve as a foundational tool for the rational design of radical polymerization processes that are both synthetically robust and environmentally responsive,” concludes Dr. Nishimura, highlighting the potential applications of the present study.
In summary, this study advances our current understanding of the reaction pathways during RROP and can contribute to the development of novel, degradable polymer materials that are also environmentally friendly.
About Assistant Professor Shin-nosuke Nishimura from Doshisha University, Japan
Dr. Shin-nosuke Nishimura serves as an Assistant Professor in the Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, Doshisha University, Japan. He completed his PhD from Doshisha University in 2019. His main research interests include polymer chemistry, biomaterials, organic chemistry, nanotechnology, and environmental chemistry. Over the years, he has published 42 papers in high Impact Factor journals that have been cited 495 times. Furthermore, he has received several awards for his research excellence, such as the Japanese and Korean Biomaterials Societies Young Scientist Exchange Program Award and the President's Award, Doshisha University.
About Professor Tomoyuki Koga from Doshisha University, Japan
Dr. Tomoyuki Koga is a professor in the Department of Molecular Chemistry and Biochemistry, Faculty of Science and Engineering, Doshisha University, Japan. He was educated at Doshisha University, where he earned his PhD in engineering in 2001. After working as a postdoctoral fellow at the National Institute of Advanced Industrial Science and Technology (AIST), Nagoya Institute of Technology, and California Institute of Technology, he moved to Doshisha University. Since 2014, he has been at Doshisha University as a full professor.
Lab page: https://polymerchem-lab.doshisha.ac.jp/en/
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