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Crystal structure of the nylon-6 α form as established by wide-angle X-ray and neutron diffraction data analyses

Polymer Journal (2025)Cite this article

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Abstract

About 70 years ago, the crystal structure of the nylon 6 α form was proposed by Bunn et al. (Bunn’s model) on the basis of wide-angle X-ray diffraction (WAXD) data analysis. The nearly extended planar-zigzag chains with alternating upward and downward orientations are regularly connected by intermolecular hydrogen bonds to form a sheet plane. These sheets are stacked regularly under the space group symmetry of P21. The quantitative analyses of WAXD and WAND data, which were measured for the first time in the present study, revealed the following. (i) Bunn’s model can be constructed using the space group P21/n of higher symmetry (this revision is important in the structure‒property discussion), (ii) but their regular model cannot reproduce both WAXD and WAND data without any issues. Moreover, (iii) the introduction of a statistically disordered up/down chain packing concept can reproduce these observed diffraction data consistently. As one local structure, the aggregation of domains has been proposed, where the domain itself consists of regular chain packing, but these domains are randomly aggregated together with the ±a/2 shift and a small c-axial shift to form a crystalline lamella. In this way, the crystal structure of the nylon-6 α form has been conclusively established.

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Acknowledgements

This work was performed with kind support from the staff of the BIX-3 and i-BIX facilities at JAEA, Tokai, Japan. The TOF experiments were performed under the proposals 2022PX3002, 2023PX3002, and 2024PX3001 of the Ibaraki Prefecture Project. This study was supported by the Grant-in-Aid for Scientific Research (B) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan (No. 22H02151).

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Authors and Affiliations

  1. Department of Future Industry-oriented Basic Science and Materials, Toyota Technological Institute, Nagoya, Japan

    Kohji Tashiro

  2. Comprehensive Research Organization for Science and Society (CROSS), Ibaraki Quantum Beam Research Center, Naka, Ibaraki, Japan

    Kohji Tashiro, Katsuhiro Kusaka & Terutoshi Sakakura

  3. Aichi Synchrotron Radiation Center Knowledge Hub Aichi, Seto, Aichi, Japan

    Kohji Tashiro

  4. Institute for Quantum Life Science, National Institutes for Quantum Science and Technology, Tokai, Ibaraki, Japan

    Kazuo Kurihara

  5. Institute for Quantum Life Science, National Institutes for Quantum Science and Technology, Chiba, Japan

    Taro Tamada

  6. Center of Quantum Life Science for Structural Therapeutics, Chiba University, Chiba, Japan

    Taro Tamada

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Tashiro, K., Kurihara, K., Tamada, T. et al. Crystal structure of the nylon-6 α form as established by wide-angle X-ray and neutron diffraction data analyses. Polym J (2025). https://doi.org/10.1038/s41428-025-01094-w

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