The common knowledge of the crystal structures of nylons dates back to the early 1950s with the work of Bunn and Garner. It describes the packing of sheets made of hydrogen-bonded stems in an extended chain conformation. These alpha phase structures have a specific powder X-ray diffraction pattern with reflections at 4.4 Å and 3.7 Å. On heating, reflections transform progressively and merge at ≈ 4.2 Å at the so-called “Brill transition”. Other diffraction patterns have been recorded for different types of nylons and thermal histories. These patterns were interpreted only as indicating the existence of “variants” of the alpha phase. However, neither their structure, nor the origin of the Brill transition were established. Recent structural analyses and molecular modeling approaches have provided new insights in these long-standing structural puzzles. The “variants” feature chain conformations that are “pleated”. The Brill transition does not involve the standard extended chains of the alpha phase but corresponds to a dynamic interconversion (≈ 10¹⁰/s) between mirror conformations of these pleated stems.

Graphic abstract

中文翻译：

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重新审视尼龙的结构和 Brill 过渡

尼龙晶体结构的常识可以追溯到 1950 年代早期 Bunn 和 Garner 的工作。它描述了由延伸链构象的氢键茎制成的薄片的堆积。这些 α 相结构具有特定的粉末 X 射线衍射图，在 4.4 Å 和 3.7 Å 处有反射。在加热时，反射逐渐转变并在 ≈ 4.2 Å 处合并，称为“布里尔转变”。对于不同类型的尼龙和热历史记录了其他衍射图案。这些模式仅被解释为表明存在 alpha 阶段的“变体”。然而，它们的结构和 Brill 过渡的起源都没有确定。最近的结构分析和分子建模方法为这些长期存在的结构难题提供了新的见解。“变体”具有“褶皱”的链构象。Brill 转变不涉及 alpha 阶段的标准扩展链，但对应于动态互变（≈ 10¹⁰ / s) 在这些褶状茎的镜像构象之间。

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