This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: 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, have 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, Ryotaro Miyazawa and Professor Koji Arimitsu—all affiliated with TUS at the time of the research.
The paper was published in the journal Macromolecules. "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," Aoki said. 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 nonionic precursor.
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