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<p>Poly(fumarate)s, which lack a methylene spacer, exhibit high glass transition temperatures because of their rigid backbone while showing unusually intense <i>β</i> relaxation in the glassy state. The microscopic origin of this seemingly paradoxical behavior remains unclear. Herein, we investigated the picosecond molecular dynamics of poly(diethyl fumarate) (PDEF) and poly(diisopropyl fumarate) (PDiPF), together with poly(methyl methacrylate) (PMMA), using quasielastic neutron scattering (QENS). PMMA exhibited larger mean square displacements (MSDs) at low temperatures because of ester methyl-group rotations, whereas poly(fumarate)s showed a steeper temperature dependence and exceeded PMMA at higher temperatures. The QENS spectra exhibited <i>Q</i>-independent linewidths, which are consistent with localized dynamics. Elastic incoherent structure factor (EISF) analysis revealed distinct behaviors for PDEF and PDiPF. PDiPF remained largely consistent with the methyl-group rotation model, whereas PDEF showed increasing deviations at higher temperatures, implying additional localized motions beyond simple methyl-group rotation. PDiPF exhibited narrower linewidths than PDEF, reflecting slower dynamics due to steric constraints of bulkier isopropyl groups. These findings suggest that the coexistence of high glass transition temperatures and strong <i>β</i> relaxation in poly(fumarate)s may arise from heterogeneous amorphous packing, where rigid regions coexist with less efficiently packed regions that accommodate localized mobility in the glassy state.</p>

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Quasielastic neutron scattering study of poly(diethyl fumarate) and poly(diisopropyl fumarate) with insights into fast dynamics and glassy relaxations

  • 期刊论文

  • 发表日期：

    2026年8月4日

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  • Sota Inagaki,
  • Hiroshi Akiba,
  • Yoshinori Ohmasa,
  • Takeshi Yamada,
  • Maiko Kofu,
  • Osamu Yamamuro,
  • Akikazu Matsumoto,
  • Yasuhito Suzuki

摘要

Poly(fumarate)s, which lack a methylene spacer, exhibit high glass transition temperatures because of their rigid backbone while showing unusually intense β relaxation in the glassy state. The microscopic origin of this seemingly paradoxical behavior remains unclear. Herein, we investigated the picosecond molecular dynamics of poly(diethyl fumarate) (PDEF) and poly(diisopropyl fumarate) (PDiPF), together with poly(methyl methacrylate) (PMMA), using quasielastic neutron scattering (QENS). PMMA exhibited larger mean square displacements (MSDs) at low temperatures because of ester methyl-group rotations, whereas poly(fumarate)s showed a steeper temperature dependence and exceeded PMMA at higher temperatures. The QENS spectra exhibited Q-independent linewidths, which are consistent with localized dynamics. Elastic incoherent structure factor (EISF) analysis revealed distinct behaviors for PDEF and PDiPF. PDiPF remained largely consistent with the methyl-group rotation model, whereas PDEF showed increasing deviations at higher temperatures, implying additional localized motions beyond simple methyl-group rotation. PDiPF exhibited narrower linewidths than PDEF, reflecting slower dynamics due to steric constraints of bulkier isopropyl groups. These findings suggest that the coexistence of high glass transition temperatures and strong β relaxation in poly(fumarate)s may arise from heterogeneous amorphous packing, where rigid regions coexist with less efficiently packed regions that accommodate localized mobility in the glassy state.