Guidotti Giulia, Soccio Michelina, García-Gutiérrez Mari Cruz, Ezquerra Tiberio, Siracusa Valentina, Gutiérrez-Fernández Edgar, Munari Andrea, Lotti Nadia
Civil, Chemical, Environmental and Materials Engineering Department, University of Bologna, Via Terracini 28, 40131 Bologna, Italy.
Instituto de Estructura de la Materia IEM-CSIC, Consejo Superior de Investigaciones Científicas, Calle Serrano 121, 28006 Madrid, Spain.
ACS Sustain Chem Eng. 2020 Jun 29;8(25):9558-9568. doi: 10.1021/acssuschemeng.0c02840. Epub 2020 Jun 1.
In the present paper, four fully biobased homopolyesters of 2,5-furandicarboxylic acid (2,5-FDCA) with a high molecular weight have been successfully synthesized by two-stage melt polycondensation, starting from the dimethyl ester of 2,5-FDCA and glycols of different lengths (the number of methylene groups ranged from 3 to 6). The synthesized polyesters have been first subjected to an accurate molecular characterization by NMR and gel-permeation chromatography. Afterward, the samples have been successfully processed into free-standing thin films (thickness comprised between 150 to 180 μm) by compression molding. Such films have been characterized from the structural (by wide-angle X-ray scattering and small-angle X-ray scattering), thermal (by differential scanning calorimetry and thermogravimetric analysis), mechanical (by tensile test), and gas barrier (by permeability measurements) point of view. The glycol subunit length was revealed to be the key parameter in determining the kind and fraction of ordered phases developed by the sample during compression molding and subsequent cooling. After storage at room temperature for one month, only the homopolymers containing the glycol subunit with an even number of -CH- groups (poly(butylene 2,5-furanoate) (PBF) and poly(hexamethylene 2,5-furanoate) (PHF)) were able to develop a three-dimensional ordered crystalline phase in addition to the amorphous one, the other two appearing completely amorphous (poly(propylene 2,5-furanoate (PPF) and poly(pentamethylene 2,5-furanoate) (PPeF)). From X-ray scattering experiments using synchrotron radiation, it was possible to evidence a third phase characterized by a lower degree of order (one- or two-dimensional), called a mesophase, in all the samples under study, its fraction being strictly related to the glycol subunit length: PPeF was found to be the sample with the highest fraction of mesophase followed by PHF. Such a mesophase, together with the amorphous and the eventually present crystalline phase, significantly impacted the mechanical and barrier properties, these last being particularly outstanding for PPeF, the polyester with the highest fraction of mesophase among those synthesized in the present work.
在本文中，以2,5-呋喃二甲酸（2,5-FDCA）的二甲酯和不同长度的二醇（亚甲基的数量范围为3至6）为原料，通过两步熔融缩聚成功合成了四种高分子量的全生物基均聚聚酯。首先通过核磁共振（NMR）和凝胶渗透色谱法对合成的聚酯进行了精确的分子表征。之后，通过压缩成型将样品成功加工成独立的薄膜（厚度在150至180μm之间）。从结构（通过广角X射线散射和小角X射线散射）、热性能（通过差示扫描量热法和热重分析）、力学性能（通过拉伸试验）和气体阻隔性能（通过渗透率测量）等角度对这些薄膜进行了表征。结果表明，二醇亚基的长度是决定样品在压缩成型和随后冷却过程中形成的有序相的种类和比例的关键参数。在室温下储存一个月后，只有含有偶数个-CH-基团的二醇亚基的均聚物（聚（2,5-呋喃二甲酸丁二醇酯）（PBF）和聚（2,5-呋喃二甲酸己二醇酯）（PHF））除了非晶相外还能够形成三维有序的结晶相，另外两种则完全呈现非晶态（聚（2,5-呋喃二甲酸丙二醇酯）（PPF）和聚（2,5-呋喃二甲酸戊二醇酯）（PPeF））。通过使用同步辐射的X射线散射实验，可以证明在所研究的所有样品中存在第三种相，其特征是有序度较低（一维或二维），称为中间相，其比例与二醇亚基的长度密切相关：发现PPeF是中间相比例最高的样品，其次是PHF。这种中间相，连同非晶相和最终可能存在的结晶相，对力学性能和阻隔性能有显著影响，对于PPeF来说，这些性能尤其突出，它是本工作中合成的中间相比例最高的聚酯。
