Nylon 5T is one of the bio‐based nylons, its raw material 1,5‐pentanediamine is derived from biomass resources and produced by biological methods. 1,5‐pentanediamine‐terephthalate (PDA‐TPA) is the monomeric salt for nylon 5T polymerization, and its own product quality has a significant impact on the performance of nylon 5T. PDA‐TPA was prepared by anti‐solvent crystallization in this study. It exists in two solid forms, a monohydrate [form (I)] and an anhydrous phase [form (II)]. The transition temperature of the two phases was around 65°C in the given ethanol–water binary (7:1) mixture. The characterization of monohydrate and anhydrate phases regarding structures and stabilities was carefully carried out using powder X‐ray diffraction, single crystal X‐ray diffraction, differential scanning calorimetry, thermogravimetric analysis, hot‐stage microscopy and Fourier transform infrared spectroscopy. The relationship between the molecular interactions of monohydrate and anhydrate phases under different packing architectures and their thermal behaviours was analysed and established. In addition, the relationships between the structures and thermal behaviours for the two solid forms were analysed and established. In addition, the effect of solvent on phase conversion, the relationships between the temperature and water activity, as well as the relative stability of monohydrate and anhydrate phases under different thermodynamic conditions, were investigated by solid–solid transformation and solvent‐mediated transformation experiments. It was obvious that the transition temperature of monohydrate and anhydrate phases of PDA‐TPA was significantly influenced by water activity, and the larger the value of water activity is, the higher is the transition temperature. These studies give insight into the transformation of nylon 5T monomer salt and contribute to the control of target crystal preparation.

中文翻译：

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1,5-戊二胺对苯二甲酸酯的晶体形式和相变：一种生物基尼龙5T单体。

尼龙5T是一种生物基尼龙，其原料1,5-戊二胺来源于生物质资源，并通过生物方法生产。1,5-戊二胺对苯二甲酸酯（PDA-TPA）是尼龙5T聚合反应的单体盐，其自身的产品质量对尼龙5T的性能有重大影响。本研究中通过反溶剂结晶制备了PDA‐TPA。它以两种固体形式存在：一水合物[形式（I）]和无水相[形式（II）]。在给定的乙醇-水二元（7：1）混合物中，两相的转变温度约为65°C。使用粉末X射线衍射，单晶X射线衍射，差示扫描量热法，热重分析法对一水合物和无水物相的结构和稳定性进行了表征 热台显微镜和傅里叶变换红外光谱。分析并建立了不同堆积结构下一水合物和无水物相的分子相互作用与它们的热行为之间的关系。此外，分析并建立了两种固体形式的结构与热行为之间的关系。此外，通过固-固转化和溶剂介导的转化实验研究了溶剂对相转化的影响，温度与水活度之间的关系以及一水合物和无水物在不同热力学条件下的相对稳定性。显然，PDA-TPA的一水合物相和无水物相的转变温度受水分活度的显着影响，水分活度值越大，转变温度越高。这些研究深入了解了尼龙5T单体盐的转化，并有助于控制目标晶体的制备。