Polyesters | 聚酯

📚 Polyesters | 聚酯

Polyesters are an important family of condensation polymers. They contain many ester linkages and are formed when monomers with hydroxyl and carboxyl groups react together with the elimination of small molecules, usually water. The most familiar example is polyethylene terephthalate, widely used in fibres and drink bottles.

聚酯是一类重要的缩聚物。它们含有许多酯键，由带有羟基和羧基的单体发生反应并脱去小分子（通常是水）形成。最常见的例子是聚对苯二甲酸乙二酯，广泛用于纤维和饮料瓶。

1. What are polyesters? | 什么是聚酯？

A polyester is a polymer whose repeating units are joined by ester linkages (–COO–). These ester groups are formed by the reaction between a hydroxyl group (–OH) and a carboxylic acid group (–COOH).

聚酯是重复单元通过酯键（–COO–）连接起来的高分子。这些酯基由羟基（–OH）与羧基（–COOH）反应形成。

Because each esterification step releases a small molecule, polyesters are classified as condensation polymers rather than addition polymers.

由于每一步酯化反应都会释放一个小分子，聚酯被归类为缩聚物，而不是加聚物。

2. Condensation polymerisation basics | 缩聚反应基础

Condensation polymerisation involves monomers with at least two functional groups. When an –OH group and a –COOH group react, they form an ester link and eliminate one water molecule.

缩聚反应涉及至少带有两个官能团的单体。当 –OH 基团与 –COOH 基团反应时，会形成一个酯键并脱去一分子水。

A general polyester formation from a diol and a dicarboxylic acid is shown below.

n HO–R–OH + n HOOC–R’–COOH → [–O–R–O–CO–R’–CO–]ₙ + 2n H₂O

二醇和二羧酸形成聚酯的一般反应如下：n HO–R–OH + n HOOC–R’–COOH → [–O–R–O–CO–R’–CO–]ₙ + 2n H₂O

The reaction must be carried out with monomers that each have two reactive groups, otherwise only a small ester molecule would form.

反应必须使用每个分子带两个反应基团的单体，否则只能形成小分子酯。

3. Common monomers: diols and dicarboxylic acids | 常见单体：二醇与二羧酸

The most common A-level example uses ethane-1,2-diol and benzene-1,4-dicarboxylic acid. Ethane-1,2-diol provides two –OH groups, while benzene-1,4-dicarboxylic acid provides two –COOH groups.

A-level 中最常见的例子使用乙二醇（ethane-1,2-diol）和对苯二甲酸（benzene-1,4-dicarboxylic acid）。乙二醇提供两个 –OH 基团，对苯二甲酸提供两个 –COOH 基团。

The diol is often called ethylene glycol, and the dicarboxylic acid is commonly called terephthalic acid. Both names are acceptable, but IUPAC names are preferred in exam answers.

这种二醇通常称为乙二醇，二羧酸通常称为对苯二甲酸。两种名称都可接受，但考试答案中优先使用 IUPAC 名称。

4. Formation of PET / Terylene | PET / 涤纶的形成

When ethane-1,2-diol and terephthalic acid undergo condensation polymerisation, the product is polyethylene terephthalate, also known as PET or Terylene.

当乙二醇与对苯二甲酸发生缩聚反应时，产物是聚对苯二甲酸乙二酯，也称 PET 或涤纶（Terylene）。

n HO–CH₂CH₂–OH + n HOOC–C₆H₄–COOH → [–O–CH₂CH₂–O–CO–C₆H₄–CO–]ₙ + 2n H₂O

n HO–CH₂CH₂–OH + n HOOC–C₆H₄–COOH → [–O–CH₂CH₂–O–CO–C₆H₄–CO–]ₙ + 2n H₂O

Notice that water is the only small molecule eliminated. The backbone of PET contains both aliphatic CH₂CH₂ units and aromatic C₆H₄ rings, which influences its strength and stiffness.

注意，水是唯一脱去的小分子。PET 的主链中既有脂肪族 CH₂CH₂ 单元，也有芳香族 C₆H₄ 环，这影响了它的强度和刚性。

5. Repeating unit and structure | 重复单元与结构

The repeating unit of PET is [–O–CH₂CH₂–O–CO–C₆H₄–CO–]ₙ. The ester linkage is the –O–CO– part, where the oxygen atom is attached to the carbonyl carbon.

PET 的重复单元是 [–O–CH₂CH₂–O–CO–C₆H₄–CO–]ₙ。酯键是 –O–CO– 部分，其中氧原子连接在

Published by TutorHao | A-Level Chemistry Revision Series | aleveler.com

更多咨询请联系16621398022（同微信）