Most commodity polyesters are synthesized via melt polycondensation of dicarboxylic acid and diol using metallic catalysts; however, the resultant metal residues can pose toxic effects on human and environment. Although polyesters can be synthesized through autocatalysis of dicarboxylic acid without additional catalysts, high molecular weight (HMW) products cannot be obtained by this strategy, which was previously attributed to the low equilibrium constant of esterification and the difficulty of removing water. Herein, we get a new understanding that the kinetic deviation of dicarboxylic acid/diol monomers is the only reason for the low molecular weight of polyesters by autocatalysis. Accordingly, we introduce a dynamic stoichiometric strategy to overcome this difficulty using anhydride-formable dicarboxylic acids as monomers through a tandem mechanism involving proton transfer, anhydride formation and re-esterification. A series of catalyst-free HMW polyesters, including poly(butylene succinate) (PBS), poly(ethylene succinate) (PES), poly(butylene succinate--butylene adipate) (PBSA), and poly(ethylene succinate--ethylene terephthalate) (PEST), were thereby synthesized. This new approach not only enables large-scale production of HMW polyesters comparable to commercial products, but also avoids the problems associated with catalysts, which is very promising for the applications with high safety requirements.

中文翻译：

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通过传统熔融缩聚无催化剂合成聚酯

大多数商品聚酯是通过二羧酸和二醇使用金属催化剂熔融缩聚合成的；然而，由此产生的金属残留物会对人类和环境造成有毒影响。虽然聚酯可以通过二元酸自催化合成，无需额外的催化剂，但通过这种策略无法获得高分子量（HMW）产品，此前这归因于酯化平衡常数低和除水困难。在此，我们得到了新的认识：二元羧酸/二醇单体的动力学偏差是自催化聚酯低分子量的唯一原因。因此，我们引入了动态化学计量策略来克服这一困难，使用可形成酸酐的二羧酸作为单体，通过涉及质子转移、酸酐形成和再酯化的串联机制。系列无催化剂高分子量聚酯，包括聚丁二酸丁二醇酯（PBS）、聚丁二酸乙二醇酯（PES）、聚丁二酸丁二醇酯-己二酸丁二醇酯（PBSA）、聚丁二酸乙二醇酯-对苯二甲酸乙二醇酯）（PEST），由此合成。这种新方法不仅能够实现与商业产品相当的高分子量聚酯的大规模生产，而且避免了与催化剂相关的问题，这对于安全要求高的应用来说非常有前景。