We report the first known instance where the formation of layered crystals in long-spaced polyesters is bypassed on rapid quenching. Aliphatic polyesters spaced by 18–48 carbons in both the diol and diacid components of the repeating unit form orthorhombic, highly symmetric, layered crystals on relatively slow or isothermal crystallization. Though the unit cell is maintained on rapid quenching to 0 °C and lamellar crystals still form, the X-ray reflection of the ester layer disappears in PE-48,48 and weakens in the shorter-spaced polyesters. Since all crystal thicknesses are larger than the distance between the two consecutive esters, the esters must be inside the crystals in a random distribution. On heating, such unlayered crystals transform into the layered type at temperatures between 45 and 60 °C, which further melt at 98–115 °C with an increasing methylene spacer in the polyester. Rapidly quenched PE-48,48 develops only the unlayered structure, while shorter-spaced polyesters form mixed unlayered and layered crystals, indicating that a larger depth of quenching is required for the development of the unlayered form with decreasing CH₂ spacer length. We posit that on fast crystallization, metastable lamellar crystals form via staggering of chain segments and random chain folding, locking a structure where the ester groups are unlayered, while on slower crystallization, ester layering is facilitated by maximizing packing of the full length of CH₂ units via van der Waals interactions and intermolecular dipolar interactions of ester units. The discovery of unlayered, metastable structures of polyethylene-like materials developed under fast cooling from the melt is important for applications that mimic those which currently utilize commercial polyethylenes and that would benefit from sustainable monomer sources and material recyclability.

中文翻译：

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可回收长间隔脂肪族聚酯中的无层-层状晶变

我们报告了第一个已知的实例，其中长间隔聚酯中层状晶体的形成在快速淬火时被绕过。重复单元的二醇和二酸组分中间隔 18-48 个碳的脂肪族聚酯在相对缓慢或等温结晶时形成正交、高度对称的层状晶体。尽管晶胞保持在快速淬火至 0 °C 并且仍然形成层状晶体，但酯层的 X 射线反射在 PE-48,48 中消失，在间隔较短的聚酯中减弱。由于所有晶体厚度都大于两个连续酯之间的距离，因此酯必须以随机分布的方式位于晶体内部。加热时，这种非层状晶体在 45 至 60 °C 的温度下转变为层状，它在 98-115°C 进一步熔化，聚酯中的亚甲基间隔物增加。快速淬火的 PE-48,48 仅形成非层状结构，而间距较短的聚酯形成混合的非层状和层状晶体，表明随着 CH 的降低，非层状形式的发展需要更大的淬火深度₂间隔长度。我们假设在快速结晶时，亚稳态层状晶体通过链段的交错和随机链折叠形成，锁定酯基未分层的结构，而在较慢的结晶中，通过最大化 CH ₂全长的堆积促进酯分层通过范德华相互作用和酯单元的分子间偶极相互作用形成单元。发现在熔体快速冷却下开发的类聚乙烯材料的非层状亚稳态结构对于模拟目前使用商业聚乙烯的应用非常重要，这些应用将受益于可持续的单体来源和材料可回收性。