New polymer designs for beyond-5G telecommunications

With the rollout of fifth-generation (5G) telecommunications networks and 6G looming on the horizon, the demand for advanced materials that can handle high-frequency signals is rising rapidly. These systems use electromagnetic waves ranging from tens to hundreds of gigahertz (GHz), where signals are highly sensitive to transmission loss, interference, and distortion. To address these issues, scientists and engineers rely on special insulating materials, known as dielectrics, which help guide signals with minimal loss.

Polymer-based dielectrics are particularly attractive. However, for high-frequency operation, they need two key traits: a low dielectric constant (D_k) and a low dissipation factor (D_f). This is important for minimizing signal transmission loss in the GHz frequency range. Until now, polymer designs that simultaneously achieve both a low D_k and a low D_f have been difficult to realize.

Addressing this challenge, a research team led by Professor Kenichi Oyaizu from the Department of Applied Chemistry, Research Institute for Science and Engineering at Waseda University in Japan has developed a new class of poly(phenylene sulfide) (PPS) derivatives with ultralow dielectric loss. “Based on our previous research on high refractive index polymers, we hypothesized that replacing oxygen with sulfur in certain polymers, such as PPO, could significantly reduce the dissipation factor,” explains Oyaizu. “Using this strategy, we succeeded in developing a new class of ultralow dielectric loss polymers.” The study, which also had contributions from Junior Researcher Seigo Watanabe of Waseda University, was published in Volume 6 of the journal Communications Materials on August 16, 2025.

Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) is currently known to offer the best balance of a low D_k and D_f. By replacing oxygen with sulfur in PPO, the researchers created poly(2,6-dimethyl-1,4-phenylene sulfide) (PMPS), a derivative of PPS. They studied the dielectric properties of PMPS at three different frequencies: 10 GHz, 40 GHz, and 80 GHz, and compared them with those of PPO. To further understand the role of sulfur, they also synthesized and studied two of its copolymers with PPO, referred to as P1 and P2, featuring an alternating sulfur and oxygen sequence.

PMPS achieved a D_k of 2.80 and an ultralow D_f of 0.00087 at 10 GHz, significantly lower than that of PPO. This improvement arises from the higher polarizability and smaller dipole moment (the measure of negative and positive charge separation) of the carbon–sulfur bond in PMPS compared to the carbon–oxygen bond in PPO. The copolymers also demonstrated excellent properties: P1 showed  a D_k of 2.76 and D_f of 0.00169, while P2 demonstrated a D_k of 2.64 and a D_f of 0.00130. A comparison of the properties of PPO, PMPS, and its copolymers indicates that increasing sulfur content is a promising strategy for reducing D_f.

The researchers also studied the frequency dependence of these properties over the 10–80 GHz range. While D_k values of all polymers did not change, D_f showed an increasing trend for PPO, PMPS and P2. Interestingly, P1 retained an almost constant D_f, achieving the lowest value among all polymers at 80 GHz. This was due to the reduced motion between its molecules. As Oyaizu explains, “The alternating sulfur-oxygen sequence in P1 and P2 results in increased intermolecular interactions, which reduce molecular mobility. Moreover, P1, specifically has a higher resistance to molecular rotation. Together, this resulted in a near-constant D_f across a wide frequency range.” Combined with strong thermal stability, this makes P1 a practical insulating material for future high-frequency telecommunications.

“Our study presents a breakthrough concept of replacing oxygen with sulfur for the design of ultralow dielectric polymers,” concludes Oyaizu. “We believe this is a first step toward practical materials that can power telecommunications beyond 5G.”

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Reference
Authors: Seigo Watanabe^1,2, Shuma Miura², Tomohiro Miura², Yoshino Tsunekawa², Daisuke Ito³ and Kenichi Oyaizu ^1,2
DOI: 10.1038/s43246-025-00917-w
Affiliations: ¹Research Institute for Science and Engineering, Waseda University, Japan
²Department of Applied Chemistry, Waseda University, Japan
³Daicel Corporation, Japan

             
About Waseda University
Located in the heart of Tokyo, Waseda University is a leading private research university that has long been dedicated to academic excellence, innovative research, and civic engagement at both the local and global levels since 1882. The University has produced many changemakers in its history, including eight prime ministers and many leaders in business, science and technology, literature, sports, and film. Waseda has strong collaborations with overseas research institutions and is committed to advancing cutting-edge research and developing leaders who can contribute to the resolution of complex, global social issues. The University has set a target of achieving a zero-carbon campus by 2032, in line with the Sustainable Development Goals (SDGs) adopted by the United Nations in 2015. 
To learn more about Waseda University, visit https://www.waseda.jp/top/en  

About Professor Kenichi Oyaizu from Waseda University, Japan
Dr. Kenichi Oyaizu is currently a Professor in the Department of Applied Chemistry at Waseda University. He obtained his PhD from Waseda University in 1995. His research focuses on the development of polymers for electron-transfer-based organic electronics and for wet-type energy storage, transport, and conversion devices. He has published approximately 300 papers on these topics. Notably, he received the Award for Encouragement of Research in Polymer Science from the Society of Polymer Science, Japan, in 2001 and the Chemical Society of Japan Award for Young Chemists in 2002.