Side substitution is an effective way of functionalizing and modifying the properties of polyamides. Meanwhile, side substitution would significantly influence the crystallization kinetics and polymorphic phase transition of polyamides, which, however, has not been well elucidated. Herein, we synthesized the side-substituted long-chain polyamides with various content of methyl pendent groups and investigated their crystallization and phase transition behaviors. We find that the thermal parameters of side-substituted polyamides vary linearly with the side group content, analogous to the isomorphic crystallization of random copolymers. All the solution-crystallized polyamides experience the α–γ Brill transition during heating, with the Brill transition temperature linearly decreasing as the side group content increases. Intriguingly, the γ–α transition of polyamides during cooling is suppressed with the presence of side methyl groups due to the difficulty in H-bond reorganization and gauche–trans conformational changes. This work has demonstrated the critical role of side substitution in the polymorphic crystallization and phase transition of long-chain polyamides.

中文翻译：

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甲基侧基取代的长链聚酰胺的线性变化的热行为和抑制的布里奇转变

侧取代是功能化和改性聚酰胺性能的有效方法。同时，侧取代会显着影响聚酰胺的结晶动力学和多晶型相变，然而这一点尚未得到很好的阐明。在此，我们合成了具有不同甲基侧基含量的侧取代长链聚酰胺，并研究了它们的结晶和相变行为。我们发现侧取代聚酰胺的热参数随侧基含量线性变化，类似于无规共聚物的同晶结晶。所有溶液结晶的聚酰胺在加热过程中都会经历α-γ布里尔转变，布里尔转变温度随着侧基含量的增加而线性降低。有趣的是，由于氢键重组和低反式构象变化的困难，聚酰胺在冷却过程中的γ-α转变因侧甲基的存在而受到抑制。这项工作证明了侧取代在长链聚酰胺的多晶型结晶和相变中的关键作用。