CNR-IPCF, National Research Council - Institute for Chemical and Physical Processes, Via Moruzzi 1, 56124 Pisa, Italy.
Department of Civil, Chemical, Environmental, and Materials, University of Bologna, Via Terracini 38, 40131 Bologna, Italy.
Biomacromolecules. 2020 Jul 13;21(7):2622-2634. doi: 10.1021/acs.biomac.0c00039. Epub 2020 Apr 28.
Furandicarboxylate-based polyesters are considered an interesting class of bio-based polymers due to their improved properties with respect to the petrol-based terephthalate homologs. An in-depth analysis of the crystal structure of poly(propylene 2,5-furandicarboxylate) (PPF), after maximum possible removal of the catalyst, was carried out. The study disclosed that purified PPF presents two different crystalline phases after crystallization from the melt. Crystallizations at temperatures lower than 120 °C lead to growth of a single crystal form (β-form), whereas two different crystal forms (α and β) were found to coexist at higher s. This behavior is opposite to that previously observed for unpurified PPF. The possibility that the catalyst nucleates the α-phase, which therefore becomes the kinetically favored modification at low crystallization temperatures in the presence of a higher amount of catalyst residue, has been considered as a feasible explanation. Two concomitantly different spherulitic morphologies were observed and connected to the β- and α-phase, respectively. The association between polymorphism and melting behavior was studied. The origin of the peaks that compose the multiple melting endotherm recorded at conventional heating rates was determined by combined wide-angle X-ray scattering, differential scanning calorimetry, fast scanning chip calorimetry, and polarized light optical microscopy measurements. The higher thermal stability of the α-crystals in comparison with the β-form was thus demonstrated.
基于呋喃二甲酸酯的聚酯由于其相对于石油基对苯二甲酸酯同系物具有改善的性能，被认为是一类有趣的生物基聚合物。对经过最大程度去除催化剂后的聚（2,5-呋喃二甲酸丙二醇酯）（PPF）的晶体结构进行了深入分析。研究表明，从熔体中结晶后，纯化的 PPF 呈现出两种不同的结晶相。在低于 120°C 的温度下结晶会导致单一晶体形式（β-形式）的生长，而在较高的温度下发现两种不同的晶体形式（α 和 β）共存。这种行为与以前观察到的未纯化的 PPF 相反。考虑到催化剂成核α相的可能性，这使得在存在更高量催化剂残留物的情况下，在较低的结晶温度下成为动力学上有利的改性，这被认为是一种可行的解释。观察到了两种同时存在的不同球晶形态，并分别与β相和α相相关联。研究了多态性和熔融行为之间的关系。通过广角 X 射线散射、差示扫描量热法、快速扫描芯片量热法和偏光显微镜测量相结合，确定了在常规加热速率下记录的多重熔融吸热峰组成的来源。因此，证明了α-晶体比β-形式具有更高的热稳定性。
