Glassy polymers are those whose chains become immobilized below their glass transition temperature. The immobilized chains make them hard and stiff, but also brittle, causing them to fracture when stretched. One promising strategy for overcoming this trade-off is to incorporate ionic groups whose reversible electrostatic attractions form physical crosslinks that improve toughness while maintaining stiffness. Although ionic liquid-based materials have demonstrated that uniformly distributed ionic interactions can improve toughness, this strategy has been difficult to apply to conventional glassy polymers. A more general molecular design strategy is therefore needed to create homogeneous ionic interactions in a wider range of glassy polymers.
Now, researchers from Tokyo University of Science (TUS), Japan, in collaboration with the Japan Science and Technology Agency (JST), Japan, developed an ionic comb polymer that combines a comb-shaped architecture with bulky 4-dimethylaminopyridine (DMAP) counterions to maintain a homogeneous nanostructure with uniformly distributed ionic interactions, enabling glassy polymers to become both stiff and tough.
The study was conducted by Dr. Daisuke Aoki (then a Junior Associate Professor in the Department of Pure and Applied Chemistry at TUS), alongside Kotaro Uchiyama (2024 graduate), Ryotaro Miyazawa (2025 graduate), and Professor Koji Arimitsu—all affiliated with TUS at the time of the research. This paper will be published in the journal Macromolecules on September 4, 2026.
"This research overturns the conventional wisdom that glassy polymers become brittle when designed using ionic interactions, demonstrating that a plastic that achieves both hardness and toughness can be created through the synergistic effect of an organic base DMAP and a comb-like structure," says Dr. Aoki.
The researchers synthesized comb polymers with poly(norbornene) backbones bearing triethylene glycol monomethyl ether side chains and carboxylic acid groups. They then neutralized the polymers with either bulky DMAP counterions or conventional sodium ions to compare how the two counterions affected the polymers' properties. Next, they evaluated the polymers' mechanical performance using tensile tests on dog-bone-shaped specimens. They then examined their thermal behavior, ionic interactions, and nanostructure using rheological measurements, Fourier-transform infrared spectroscopy, synchrotron small-angle and wide-angle X-ray scattering (SAXS/WAXS).
High concentrations of sodium ions made the polymers increasingly brittle. In contrast, DMAP improved mechanical performance across a broad range of counterion concentrations. The best-performing DMAP-neutralized ionic comb polymer achieved an exceptional toughness of approximately 137 MJ/m³ together with a high Young's modulus of approximately 0.9 GPa—approximately four times tougher and twice as stiff as the non-ionic precursor.
SAXS/WAXS revealed that DMAP forms a homogeneous nanostructure with no detectable nanoscale phase separation, while infrared spectroscopy confirmed ionization within the polymer. Rheological tests further revealed that DMAP lowers the glass transition temperature from 96 °C to 81 °C, allowing greater polymer chain mobility by acting as a plasticizer. Together, the comb-shaped polymer architecture and DMAP enabled the material to achieve both hardness and toughness.
"DMAP functions both as a plasticizer and a physical crosslinking point, creating a unique nanostructure that we call 'soft crosslinking', " says Dr. Aoki.
This approach provides an alternative to ionic liquid-based toughening strategies and establishes a new strategy for developing stronger and more durable glassy plastics.
"Applying this finding of achieving both hardness and toughness in glassy polymers to more widespread molecular designs will lead to the development of next-generation plastic materials that are less prone to breakage and have a longer lifespan. In the future, these longer-lasting materials could reduce plastic waste, and if used as structural materials for transportation equipment such as drones and automobiles, they could also contribute to lower carbon dioxide emissions and improved energy efficiency through lightweight designs," says Dr. Aoki.
Reference
Title of original paper: Anomalous Toughening of Glassy Ionic Comb Polymers: Retention of Homogeneity Achieved by Bulky 4-Dimethylaminopyridinium Counterions
Journal: Macromolecules
DOI: https://doi.org/10.1021/acs.macromol.6c00773
About The Tokyo University of Science
Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan's development in science through inculcating the love for science in researchers, technicians, and educators.
With a mission of "Creating science and technology for the harmonious development of nature, human beings, and society," TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today's most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.
Website: https://www.tus.ac.jp/en/mediarelations/
About Junior Associate Professor Daisuke Aoki from Tokyo University of Science
Dr. Daisuke Aoki was formerly a Junior Associate Professor in the Department of Pure and Applied Chemistry at Tokyo University of Science (TUS), Japan, where this research was conducted. He earned his Ph.D. in Engineering from the Nara Institute of Science and Technology in 2021. His research focuses on polymer chemistry, specifically developing elastic patterning for plastics based on neutralization reactions. Aoki has received numerous accolades, including the 2025 Award for Encouragement of Research in Polymer Science and multiple front cover features in prestigious journals like Macromolecular Rapid Communications and Polymer Journal. He was also recognized as a Rising Star in Polymer Science in 2025.
https://arilab.ci.noda.tus.ac.jp/
Funding information
This study was supported by the JSPS KAKENHI grant number JP23K13802 and JP25K18081 (Early-Career Scientists), JST ACT-X Grant Number JPMJAX24D1, the Joint Usage/Research Center for Catalysis (25AY0813), and the Tokyo University of Science.
