Bio-based polyamide 56 is a new type of bio-based polyamide that is regarded as a most promising material for the textile industry. High-quality polymer materials require first high-quality monomers. In this report, we investigated the solid–liquid equilibrium of polyamide 56 salt (an ionic solid compound used to prepare polyamide 56), thermodynamic parameters of the dissolution process, and the crystallization process, and screened out a favorable crystallization system to obtain a high-quality product. The dissolution was shown to be endothermic and not a spontaneous process; entropy was the overall driving force for the dissolution. The crystallization process and the effect of impurities were investigated. Cooling crystallization in pure water was beneficial to the nucleation and crystal growth of polyamide 56 salt, and is a good choice from the perspective of economy and the stability of the product. Additionally, the crystal structural characteristics and thermal behavior were systematically characterized by single crystal X-ray diffraction (SSRD), powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). It was found that there were two crystal forms of polyamide 56 salt, dihydrate and anhydrate. The dihydrate was a stable crystal form, and the anhydrous form could be converted into the dihydrate by absorbing moisture. The temperature 183.7 °C was the onset of 1,5-pentanediamine cation deprotonation and adipic acid anion protonation rather than their degradation. These contributions provide a potential industrial preparation strategy for high-quality polyamide 56 salt, as well as laying a foundation for its polymerization.

中文翻译：

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生物基聚酰胺56盐的晶体结构，热力学和结晶

生物基聚酰胺56是一种新型的生物基聚酰胺，被认为是纺织工业中最有希望的材料。高质量的聚合物材料首先需要高质量的单体。在本报告中，我们研究了聚酰胺56盐（用于制备聚酰胺56的离子型固体化合物）的固液平衡，溶解过程的热力学参数以及结晶过程，并筛选出有利的结晶体系以获得较高的优质的产品。溶出度是吸热的，不是自发过程。熵是溶解的总体驱动力。研究了结晶过程和杂质的影响。在纯水中冷却结晶有利于聚酰胺56盐的形核和晶体生长，从经济性和产品稳定性的角度来看，这是一个不错的选择。另外，通过单晶X射线衍射（SSRD），粉末X射线衍射（PXRD），差示扫描量热法（DSC）和热重分析（TGA）系统地表征了晶体的结构特征和热行为。发现聚酰胺56盐有两种晶体形式，二水合物和无水物。二水合物是稳定的晶体形式，无水形式可以通过吸收水分而转化为二水合物。183.7°C是1,5-戊二胺阳离子去质子化和己二酸阴离子质子化的开始，而不是它们的降​​解。这些贡献为高品质聚酰胺56盐的工业制备提供了潜在的策略，