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<p>Adjusting the structure of the hard segment (HS) represents a key method for manipulating the mechanical properties of thermoplastic polyurethane (TPU). This study developed a novel molecular design strategy to tailor TPU’s mechanical performance through altering the terminal diisocyanate structure of HS. The typical HDI-BDO based TPU was chosen as a model. Replacing HS’s terminal HDI residues with aromatic PPDI, TODI, and MDI (the corresponding TPUs are named as 2P, 2TO, and 2M, respectively) enabled broad tuning of TPU’s Young’s modulus while maintaining high tensile strength and elongation. Compared with linear PPDI and TODI, the bent and unsymmetrical MDI exhibits greater deviation from the central axis of the middle HDI-BDO segment, which reduces HS’s capability of three-dimensionally ordered packing. Therefore, 2P and 2TO show higher hydrogen bond content and crystallinity, stronger physical crosslinking network, and thus much higher Young’s modulus than 2M (75.6 MPa). Besides geometric structure, <i>π</i>–<i>π</i> stacking between HS’s terminal aromatic diisocyanates critically governs TPU’s physical crosslinking network. In 2P, <i>π</i>–<i>π</i> stacking induces torsion of the middle HDI-BDO segment and disrupts the neighboring hydrogen bonds, leading to a dense network with fine hard blocks. In contrast, the lateral methyl groups in TODI hinder <i>π</i>–<i>π</i> stacking, resulting in a sparse network with large hard blocks. Accordingly, 2TO exhibits a higher Young’s modulus (146.2 MPa) than 2P (124.0 MPa), but greater strain-rate sensitivity.</p>

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A Strategy to Tailor Mechanical Properties of Thermoplastic Polyurethane through Altering the Terminal Diisocyanate Structure of Hard Segment

  • 期刊论文

  • 发表日期：

    2025年11月19日

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  • Ze-Hao Wang,
  • Chen-Ding Wang,
  • Xiao-Li Zhao,
  • Xiao-Niu Yang

摘要

Adjusting the structure of the hard segment (HS) represents a key method for manipulating the mechanical properties of thermoplastic polyurethane (TPU). This study developed a novel molecular design strategy to tailor TPU’s mechanical performance through altering the terminal diisocyanate structure of HS. The typical HDI-BDO based TPU was chosen as a model. Replacing HS’s terminal HDI residues with aromatic PPDI, TODI, and MDI (the corresponding TPUs are named as 2P, 2TO, and 2M, respectively) enabled broad tuning of TPU’s Young’s modulus while maintaining high tensile strength and elongation. Compared with linear PPDI and TODI, the bent and unsymmetrical MDI exhibits greater deviation from the central axis of the middle HDI-BDO segment, which reduces HS’s capability of three-dimensionally ordered packing. Therefore, 2P and 2TO show higher hydrogen bond content and crystallinity, stronger physical crosslinking network, and thus much higher Young’s modulus than 2M (75.6 MPa). Besides geometric structure, π–π stacking between HS’s terminal aromatic diisocyanates critically governs TPU’s physical crosslinking network. In 2P, π–π stacking induces torsion of the middle HDI-BDO segment and disrupts the neighboring hydrogen bonds, leading to a dense network with fine hard blocks. In contrast, the lateral methyl groups in TODI hinder π–π stacking, resulting in a sparse network with large hard blocks. Accordingly, 2TO exhibits a higher Young’s modulus (146.2 MPa) than 2P (124.0 MPa), but greater strain-rate sensitivity.