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<p>Quantifying the hydrogen bond (H-bond) strength of polymers is essential for rational design of advanced materials. However, direct measurement remains challenging because of the structural complexity of polymers and the weak nature of H-bonds. Vacuum-based single-molecule force spectroscopy (Vac-SMFS) offers a new and precise approach for such measurements. Using polyallylamine (PAAm) as a model polymer, the intrinsic strength (<i>i.e.</i>, strength without external influences) of representative N—H⋯N H-bonds was quantified to be about 5.25 kJ·mol<sup>−1</sup>. Comparative Vac-SMFS analysis across different polymer systems revealed that the N —H⋯N H-bonds in PAAm are unexpectedly stronger than the N—H⋯O H-bonds in poly(<i>N</i>-isopropylacrylamide) (PNIPAM) and the O—H⋯O H-bonds in poly(hydroxyethyl methacrylate) (PHEMA). This trend contrasts with that of established small-molecule systems. These results highlight how side-chain length and spatial configuration dictate polymer H-bond strengths, expanding the fundamental knowledge of polymer interactions and enabling the rational design of next-generation functional materials.</p>

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Unexpectedly Robust N–H⋯N Hydrogen Bonds in an Individual Polyallylamine Chain

  • 期刊论文

  • 发表日期：

    2026年1月15日

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  • Yu-Chen Wang,
  • Ming-Han Hu,
  • Dong Ding,
  • Wen-Tao Yuan,
  • Yu Bao,
  • Shu-Xun Cui

摘要

Quantifying the hydrogen bond (H-bond) strength of polymers is essential for rational design of advanced materials. However, direct measurement remains challenging because of the structural complexity of polymers and the weak nature of H-bonds. Vacuum-based single-molecule force spectroscopy (Vac-SMFS) offers a new and precise approach for such measurements. Using polyallylamine (PAAm) as a model polymer, the intrinsic strength (i.e., strength without external influences) of representative N—H⋯N H-bonds was quantified to be about 5.25 kJ·mol−1. Comparative Vac-SMFS analysis across different polymer systems revealed that the N —H⋯N H-bonds in PAAm are unexpectedly stronger than the N—H⋯O H-bonds in poly(N-isopropylacrylamide) (PNIPAM) and the O—H⋯O H-bonds in poly(hydroxyethyl methacrylate) (PHEMA). This trend contrasts with that of established small-molecule systems. These results highlight how side-chain length and spatial configuration dictate polymer H-bond strengths, expanding the fundamental knowledge of polymer interactions and enabling the rational design of next-generation functional materials.