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Role of flexible spacers in achieving photoinduced phase transitions of azobenzene-based liquid-crystalline polymers at room temperature

Polymer Journal volume 56, pages 1061–1067 (2024)Cite this article

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Abstract

The photoinduced solid‒liquid phase transition is a fascinating phenomenon that can be utilized for a range of applications, including debondable adhesives, photolithography, and soft actuators; however, developing polymers with this function is not trivial. In this work, we report an azobenzene (Azo)-containing polymer capable of rapid room-temperature photoliquefaction upon UV irradiation and elucidate the design principles for photoliquefying polymers that harness the photothermal effect. We prepare a series of Azo polymers by coupling diacrylate Azo with dithiol-functionalized flexible spacers of different lengths, such as ethylene glycol (EG), hexa(ethylene glycol) (HEG), and poly(ethylene glycol) (PEG). EG-Azo, with the shortest spacer, has a high melting temperature (Tm) of 78 °C due to the strong interactions among the liquid-crystalline Azo molecules. Owing to the high Tm, EG-Azo does not exhibit a photoinduced solid‒liquid phase transition, although it has the greatest photothermal effect among the polymers (temperature rise to 50 °C). The incorporation of the longer spacers effectively decreases the Tm of the Azo polymers. For example, PEG-Azo possesses a reduced Tm of 40 °C, thereby enabling photoliquefaction at room temperature after only 1 min of UV irradiation. PEG-Azo can be reversibly returned to a solid-state within 5 min after the UV light is turned off.

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Acknowledgements

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MSIT) (RS-2023-00212143). This work was also supported by the H2KOREA funded by the Ministry of Education (2022Hydrogen fuel cell-003, Innovation Human Resources Development Project for Hydrogen Fuel Cells). This work was also supported by the Chung-Ang University Research Scholarship Grants in 2022. We would like to thank Prof. Dae Seok Kim and Hye Joo Lee at Pukyong National University for their help with the GPC measurements.

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  1. Department of Chemical Engineering, Chung-Ang University, Seoul, 06974, Republic of Korea

    Yujin Kang, Donguk Kim & Changyeon Lee

  2. Department of Polymer Science and Engineering, Kumoh National Institute of Technology, Gumi, Gyeongbuk, 39177, Republic of Korea

    Wonho Lee

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  1. Yujin Kang
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  2. Donguk Kim
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Correspondence to Wonho Lee or Changyeon Lee.

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Kang, Y., Kim, D., Lee, W. et al. Role of flexible spacers in achieving photoinduced phase transitions of azobenzene-based liquid-crystalline polymers at room temperature. Polym J 56, 1061–1067 (2024). https://doi.org/10.1038/s41428-024-00946-1

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