生物基聚酯是一类源自可再生生物资源的聚合物，对于减轻当前资源浪费与环境污染具有重要意义。然而生物基聚酯的传统合成方法常使用有机溶剂和金属催化剂，这不仅会危害生态环境，也对人类健康构成潜在威胁。低共熔溶剂（DES）作为一种新型的绿色溶剂，在有机合成、萃取分离和聚合反应等领域已有广泛的应用。目前基于DES制备生物基聚酯的研究主要集中于将DES作为分散介质，实现生物基聚酯的合成。本论文提出了一种在DES中制备两种生物基聚酯的方法，所合成的DES具有分散介质与催化合成聚酯的双功能，为实现生物基聚酯的绿色合成提供了新思路。主要工作如下：

1. 选用1种氢键受体（氯化胆碱）和7种不同的氢键供体（尿素、乙二醇、乳酸、苯磺酸、甲烷磺酸、草酸和对甲苯磺酸）组合制得了7种二元DES和5种基于氯化胆碱、草酸和对甲苯磺酸的三元DES。利用核磁共振氢谱、傅里叶变换红外光谱和理论计算的方法深入探讨了DES的分子间相互作用、分子结构和静电势分布。利用紫外可见吸收光谱的结果计算了DES的Hammett酸度（H₀），H₀越小，酸性越强。其中二元DES的酸性大小顺序为ChCl-2Urea < ChCl-2EG < ChCl-LA < ChCl-2BSA < ChCl-3MSA < ChCl-OA < ChCl-2TsOH。利用热重分析、流变粘度测试分析等手段表征了DES的热稳定性和粘度特性，DES的热稳定性较好（热分解温度大于200 ℃），粘度适中（部分DES的粘度低于1000 mpa·s）。相关DES结构和性质的研究为后续在生物基聚酯合成的应用奠定了基础。

2. 在上述7种二元DES和5种三元DES中系统地研究了聚丁二酸丁二醇酯（PBS）的合成。改变DES种类、DES用量、反应温度和反应时间等条件，制得了不同重均分子量的PBS，整个反应过程中不需要额外添加金属催化剂和传统有机溶剂。通过分析核磁共振氢谱和凝胶渗透色谱的结果，发现ChCl-3TsOH-OA体系具有优异的催化效果，在该体系内获得了重均分子量较高的PBS（43900 g/mol）。通过理论计算证明了在ChCl-3TsOH-OA体系中制备PBS的作用机制，即DES的酸性组分提供了部分氢质子，使反应的活化能下降，缩聚反应更容易进行。

3. 在DES中制备了聚2,5-呋喃二甲酸己二醇酯（PHF）。以生物基2,5-呋喃二甲酸二甲酯（DMFD）和1,6-己二醇（1,6-HDO）为单体，通过对DES用量、反应温度和反应时间等反应条件进行优化，在ChCl-3TsOH-OA体系中制备了数均分子量3800 g/mol的PHF。通过核磁共振氢谱表征和理论计算的方法，探究了DES在酯交换聚合反应中的作用机制，ChCl-3TsOH-OA体系不仅能提供氢质子催化酯交换反应，还能与1,6-HDO形成氢键，进而活化了1,6-HDO的羟基氧原子，有利于进攻DMFD的羰基碳原子。理论计算表明引入TsOH后，体系的反应活化能降低，证明了ChCl-3TsOH-OA体系在合成PHF的反应中兼具分散和催化的双重功能。

Bio-based polyesters, as renewable biological polymers, play a crucial role in mitigating current resource depletion and environmental degradation. However, conventional methods for their synthesis often rely on organic solvents and metal catalysts, posing risks to both ecosystems and human health. In contrast, deep eutectic solvents (DESs), recognized for their eco-friendly properties, have found widespread applications in organic synthesis, extraction, separation, and polymerization reactions. Current research on the synthesis of bio-based polyesters using DES primarily focuses on employing DES as a dispersing medium to facilitate the synthesis of these polyesters. This paper proposes a method for synthesizing two types of bio-based polyesters in DESs, where the DES serves a dual function as both a dispersing medium and a catalyst for the polyester synthesis. This approach provides a novel perspective for the green synthesis of bio-based polyesters.

Firstly, seven binary DESs were prepared with one hydrogen bond acceptor (choline chloride) and seven different hydrogen bond donors (urea, ethylene glycol, lactic acid, benzenesulfonic acid, methanesulfonic acid, oxalic acid, and p-toluenesulfonic acid). In addition, five ternary DESs based on choline chloride, oxalic acid, and p-toluenesulfonic acid with varying compositions were prepared. The analyses of ¹H NMR, FTIR and theoretical calculations were used to deeply investigate the intermolecular interactions, molecular structures, and electrostatic potential distributions of DESs. The measurements of DESs acidity were conducted by Hammett acidity functions using 4-nitrodiphenylamine as an indicator by UV–vis spectroscopy. The acidity of binary DESs increases in the following order: ChCl-2Urea < ChCl-2EG < ChCl-LA < ChCl-2BSA < ChCl-3MSA < ChCl-OA < ChCl-2TsOH. The thermostability and viscosity of DESs were measured by thermal gravimetric analyses and rheological measurements. The DESs showed good thermal stability when the decomposition temperature greater than 200 ℃ and moderate viscosity (viscosity of partial DESs lower than 1000 mpa·s).

The syntheses of polybutylene succinate (PBS) were systematically investigated in seven binary DESs and five ternary DESs. Various conditions, including DES type, DES concentration, reaction temperature and reaction time, were modified to obtain PBS with different weight-average molecular weights. This method eliminates the need for metal catalysts and additional organic solvents. Analysis of ¹H NMR spectra and GPC revealed that the ChCl-3TsOH-OA system exhibited outstanding catalytic performance, yielding PBS with a high weight-average molecular weight (43900 g/mol). Theoretical calculation results demonstrated that in the ChCl-3TsOH-OA system, the acidic components of DES provided partial hydrogen protons, reducing the activation energy of the reaction.

Poly(hexamethylene-2,5-furanoate) (PHF) was synthesized using DESs. Bio-based dimethyl 2,5-furandicarboxylate (DMFD) and 1,6-hexanediol (1,6-HDO) were used as polymerization monomers. In this work, polymerization conditions including DES concentration, reaction temperature and reaction time were optimized. Consequently, in the ChCl-3TsOH-OA system, PHF with a relatively high number-average molecular weight of 3800 g/mol was successfully synthesized. The mechanism of DES in transesterification polymerization was investigated by analyzing ¹H NMR spectra and theoretical calculations. It was found that the ChCl-3TsOH-OA system not only catalyzed the transesterification reaction by providing hydrogen protons but also formed hydrogen bonds with 1,6-HDO. These hydrogen bonds activated the hydroxyl oxygen atom of 1,6-HDO, facilitating its attack on the carbonyl carbon atom of DMFD. Theoretical calculation results indicated that the addition of TsOH reduced the reaction activation energy, confirming the dual dispersion and catalysis functions of the ChCl-3TsOH-OA system in PHF synthesis.