📚 Polyesters: Synthesis, Properties and Applications | 聚酯：合成、性质与应用
Polyesters are an important class of condensation polymers, formed by the reaction between monomers containing two reactive functional groups, such as dicarboxylic acids and diols, or by self-condensation of hydroxycarboxylic acids. The ester linkage (-COO-) is the characteristic feature of these polymers. They are widely used in textiles, packaging, and engineering plastics due to their versatility and recyclability.
聚酯是一类重要的缩聚物，由含有两个活性官能团的单体（如二元羧酸与二元醇）反应生成，或通过羟基羧酸的自身缩合而成。酯键（-COO-）是这类聚合物的特征。由于其多功能性和可回收性，它们广泛用于纺织、包装和工程塑料领域。
1. What are Polyesters? | 什么是聚酯？
Polyesters are polymers that contain ester functional groups in their main chain. They are formed by condensation polymerisation, a process in which monomers join together with the elimination of small molecules, usually water. The repeating units are linked by ester bonds (-COO-). This differs from addition polymers, which form without the loss of small molecules.
聚酯是主链中含有酯官能团的聚合物。它们通过缩聚反应形成，这一过程中单体相互结合并脱去小分子（通常是水）。重复单元通过酯键（-COO-）相连。这与加聚物不同，后者形成时不脱去小分子。
2. Condensation Polymerisation Mechanism | 缩聚反应机理
In condensation polymerisation, each monomer must have at least two functional groups so that the chain can grow in two directions. For polyester formation, the reaction involves the hydroxyl group (-OH) of a diol and the carboxyl group (-COOH) of a dicarboxylic acid, or both groups present in the same molecule (a hydroxycarboxylic acid). Each ester link formed releases one water molecule.
在缩聚反应中，每个单体必须至少有两个官能团，使得链可以在两个方向上增长。对于聚酯的形成，反应涉及二醇的羟基（-OH）和二元羧酸的羧基（-COOH），或存在于同一分子中的两种基团（羟基羧酸）。每形成一个酯键会释放一个水分子。
3. Monomers: Dicarboxylic Acids and Diols | 单体：二元羧酸与二元醇
Typical dicarboxylic acids used include terephthalic acid (benzene-1,4-dicarboxylic acid) and ethane-1,2-diol (ethylene glycol). These are the monomers for the most common polyester, PET. The acid provides two -COOH groups, while the diol provides two -OH groups. By alternating these monomers, a long polymer chain with ester linkages is built.
常用的二元羧酸包括对苯二甲酸（1,4-苯二甲酸）和乙二醇（1,2-乙二醇）。它们是最常见的聚酯PET的单体。该酸提供两个羧基，而二醇提供两个羟基。通过这些单体的交替连接，构建出具有酯键的长聚合物链。
The general equation for the reaction between a dicarboxylic acid (HOOC-R-COOH) and a diol (HO-R'-OH) is shown below. For every repeat unit, two water molecules are produced, as two ester bonds are formed between each pair of monomers.
二元羧酸（HOOC-R-COOH）与二元醇（HO-R'-OH）反应的通式如下。每生成一个重复单元，产生两分子水，因为每对单体之间形成了两个酯键。
n HOOC—R—COOH + n HO—R'—OH → —(—O—R'—O—CO—R—CO—)ₙ— + 2n H₂O
4. Monomers: Hydroxycarboxylic Acids | 单体：羟基羧酸
c acid) or glycolic acid. The polymerisation of lactic acid produces poly(lactic acid) (PLA), a biodegradable polyester. The reaction is: n HO-R-COOH → -[O-R-CO]n- + (n-1) H2O.
聚酯也可以由同时含有羟基和羧基的单一种类单体制成，例如乳酸（2-羟基丙酸）或乙醇酸。乳酸的聚合生成可生物降解的聚酯——聚乳酸（PLA）。反应式为：n HO-R-COOH → -[O-R-CO]ₙ- + (n-1) H
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