Thin crystal melting produces the low-temperature endotherm in ethylene/methacrylic acid ionomers

Yueh Lin Loo, Katsuyuki Wakabayashi, Y. Evelyn Huang, Richard Alan Register, Benjamin S. Hsiao

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53 Scopus citations


Upon extended aging at room temperature, ethylene/methacrylic acid (E/MAA) ionomers develop an endotherm near 50 °C in their differential scanning calorimetry traces. The origin of this low-temperature endotherm has been the subject of considerable debate, in part because direct structural probes have been little applied to its study. Here, we use in situ small-angle X-ray scattering and wide-angle X-ray diffraction to show that this endotherm reflects the melting of thin polyethylene crystals, which gradually develop following primary crystallization. These secondary crystals form within the amorphous layers separating primary crystals. When the framework of primary crystals is oriented by crystallization during flow, the secondary crystals follow this orientation, indicating that the secondary crystals are not isometric fringed micelles but instead have a substantial lateral extent.

Original languageEnglish (US)
Pages (from-to)5118-5124
Number of pages7
Issue number14
StatePublished - Jun 27 2005

All Science Journal Classification (ASJC) codes

  • Organic Chemistry
  • Polymers and Plastics
  • Materials Chemistry


  • Ionomer
  • Secondary crystals
  • Small-angle X-ray scattering


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