Polymers: Key Concepts for A-Level Edexcel Chemistry | A-Level Edexcel 化学：聚合物考点精讲

📚 Polymers: Key Concepts for A-Level Edexcel Chemistry | A-Level Edexcel 化学：聚合物考点精讲

Polymers are everywhere – from the plastics in our everyday lives to the biological macromolecules that make up living organisms. In Edexcel A-Level Chemistry, polymerisation is a core topic that bridges organic chemistry and real-world applications. Understanding how small monomers join to form long chains, the differences between addition and condensation polymerisation, and how to deduce structures from repeat units is essential for exam success. This article breaks down every key concept you need, with paired English and Chinese explanations, worked examples, and targeted exam tips.

聚合物无处不在——从日常生活中的塑料到构成生物体的生物大分子。在 Edexcel A-Level 化学中，聚合是一个连接有机化学与现实应用的核心主题。理解小分子单体如何连接形成长链、加成聚合与缩合聚合的区别，以及如何从重复单元推导结构是考试成功的关键。本文逐一解析你需要的每一个关键概念，配有中英文对照讲解、实例分析和应试技巧。

1. Introduction to Polymerisation | 聚合反应简介

A polymer is a long-chain molecule made from many small repeating units called monomers. The process of linking monomers together is polymerisation. Polymers can be natural, like proteins and DNA, or synthetic, like polythene and nylon. The physical properties of a polymer depend on the monomer structure, chain length, branching, and intermolecular forces between chains.

聚合物是由许多称为单体的小重复单元组成的长链分子。将单体连接起来的过程称为聚合。聚合物可以是天然的，如蛋白质和 DNA，也可以是合成的，如聚乙烯和尼龙。聚合物的物理性质取决于单体结构、链长、支化程度以及链之间的分子间作用力。

There are two principal types of polymerisation: addition polymerisation, which involves unsaturated monomers (usually alkenes), and condensation polymerisation, which involves monomers with two functional groups and typically releases a small molecule such as water or HCl. Edexcel requires you to identify the type, draw the repeat unit, and predict the polymer structure from given monomers, and vice versa.

聚合主要有两种类型：加成聚合，涉及不饱和单体（通常是烯烃）；缩合聚合，涉及带有两个官能团的单体，通常释放小分子如水或 HCl。Edexcel 要求你能够识别聚合类型、绘制重复单元，并根据给定的单体预测聚合物结构，反之亦然。

2. Addition Polymerisation | 加成聚合

Addition polymerisation occurs when unsaturated monomers (alkenes or substituted alkenes) open their double bonds and join together in a chain through a free-radical mechanism. No other product is formed; the empirical formula of the polymer is the same as that of the monomer. The reaction is initiated by heat, UV light, or peroxide initiators, which generate radicals that attack the C=C bond.

加成聚合发生时不饱和单体（烯烃或取代烯烃）打开双键，通过自由基机理连接成链。没有其他产物生成；聚合物的经验式与单体相同。反应由热、紫外光或过氧化物引发剂引发，产生自由基攻击 C=C 键。

The general equation for addition polymerisation of ethene is:

n CH₂=CH₂ → (-CH₂-CH₂-)ₙ

乙烯加成聚合的通式为：

n CH₂=CH₂ → (-CH₂-CH₂-)ₙ

The repeat unit is shown inside square brackets with a subscript n. When drawing the repeat unit, you must show the extension bonds through the brackets. For poly(ethene), it is -[CH₂-CH₂]-. For substituted alkenes like chloroethene, the repeat unit is -[CH₂-CHCl]-.

重复单元写在方括号内，下标为 n。绘制重复单元时，必须显示穿过括号的延伸键。对于聚乙烯，重复单元是 -[CH₂-CH₂]-；对于氯乙烯等取代烯烃，重复单元是 -[CH₂-CHCl]-。

3. Examples of Addition Polymers | 加成聚合物实例

Common addition polymers you must know include poly(ethene) (polythene), poly(propene), poly(chloroethene) (PVC), poly(phenylethene) (polystyrene), and poly(tetrafluoroethene) (PTFE, Teflon). Table 1 summarises the monomer and its polymer repeat unit:

你必须熟悉的常见加成聚合物包括聚乙烯、聚丙烯、聚氯乙烯 (PVC)、聚苯乙烯和聚四氟乙烯 (PTFE, 特氟龙)。表1总结了单体及其聚合物重复单元：

Monomer	Polymer repeat unit	Uses
CH₂=CH₂ (ethene)	-CH₂-CH₂-	Plastic bags, bottles
CH₂=CHCH₃ (propene)	-CH₂-CH(CH₃)-	Ropes, carpets, medical devices
CH₂=CHCl (chloroethene)	-CH₂-CHCl-	Window frames, pipes
CH₂=CH(C₆H₅) (phenylethene)	-CH₂-CH(C₆H₅)-	Packaging, insulation
CF₂=CF₂ (tetrafluoroethene)	-CF₂-CF₂-	Non-stick coatings

You must be able to draw the repeat unit given the monomer, and vice versa. Remember that the repeat unit is the smallest part of the chain that repeats; you do not include the terminal groups. For poly(propene), the repeat unit is -CH₂-CH(CH₃)- not -CH(CH₃)-CH₂- because the orientation follows the carbon backbone.

你必须能够根据单体画出重复单元，反之亦然。记住重复单元是重复的最小部分；不包括末端基团。对于聚丙烯，重复单元是 -CH₂-CH(CH₃)- 而非 -CH(CH₃)-CH₂-，因为方向遵循碳骨架。

4. Condensation Polymerisation | 缩合聚合

Condensation polymerisation involves monomers with two reactive functional groups per molecule. Each time two monomers join, a small molecule such as water or hydrogen chloride is eliminated. The empirical formula of the polymer is not the same as that of the monomers because atoms are lost in the condensation. This type of polymerisation produces polyesters and polyamides.

缩合聚合涉及每个分子带两个反应性官能团的单体。每次两个单体连接时，都会脱去一个小分子，如水或氯化氢。聚合物的经验式与单体的不同，因为缩合过程中失去了原子。这类聚合反应生成聚酯和聚酰胺。

For a condensation polymer, the repeat unit is derived from the two monomers linked by the functional group that forms the backbone. When drawing the repeat unit, you show the ester or amide link and the extension bonds at both ends. Edexcel often tests drawing the repeat unit from given monomer structures, especially for diols + dicarboxylic acids or diamines + dicarboxylic acids.

对于缩合聚合物，重复单元由两个单体通过形成主链的官能团连接而成。绘制重复单元时，要显示酯键或酰胺键以及两端的延伸键。Edexcel 经常考查根据给定单体结构绘制重复单元，尤其是二醇+二羧酸或者二胺+二羧酸的组合。

5. Polyesters | 聚酯

A polyester is formed from a diol and a dicarboxylic acid (or a diacyl chloride) through esterification. Each ester link forms with the loss of a water molecule. The most common example is Terylene, made from benzene-1,4-dicarboxylic acid and ethane-1,2-diol. The repeat unit contains the ester group -CO-O- (often written as -COO-).

聚酯由二醇和二羧酸（或二酰氯）通过酯化反应形成。每形成一个酯键就失去一个水分子。最常见的例子是涤纶，由苯-1,4-二甲酸和乙-1,2-二醇制成。重复单元包含酯基 -CO-O-（常写作 -COO-）。

Equation for Terylene formation:

n HOOC-C₆H₄-COOH + n HO-CH₂-CH₂-OH → (-OC-C₆H₄-COO-CH₂-CH₂-O-)ₙ + 2n H₂O

涤纶生成的方程：

n HOOC-C₆H₄-COOH + n HO-CH₂-CH₂-OH → (-OC-C₆H₄-COO-CH₂-CH₂-O-)ₙ + 2n H₂O

When drawing the repeat unit for a polyester, always show the ester link clearly: -COO- with the carbonyl oxygen double-bonded to carbon. Also, you can form polyesters from a single monomer containing both hydroxyl and carboxyl groups, like lactic acid forming poly(lactic acid) (PLA), a biodegradable polymer.

在绘制聚酯的重复单元时，要清晰地显示酯键：-COO-，其中羰基氧与碳双键连接。也可以由同时含有羟基和羧基的单一单体形成聚酯，例如乳酸形成聚乳酸 (PLA)，一种可生物降解的聚合物。

6. Polyamides | 聚酰胺

A polyamide is formed from a diamine and a dicarboxylic acid, or from a single amino acid. Each amide link (-CONH-) forms with the loss of a water molecule. Nylon-6,6 is a classic example, made from 1,6-diaminohexane and hexane-1,6-dioic acid. The name ‘6,6’ refers to the number of carbon atoms in each monomer.

聚酰胺由二胺和二羧酸形成，或由单一氨基酸形成。每个酰胺键 (-CONH-) 形成时失去一个水分子。尼龙-6,6 是经典例子，由 1,6-二氨基己烷和己烷-1,6-二酸制成。名称中的 ‘6,6’ 指每个单体中的碳原子数。

Repeat unit of Nylon-6,6: (-NH-(CH₂)₆-NH-CO-(CH₂)₄-CO-)ₙ. Notice the amide group orientation; it can also be drawn as -NH-CO- linking the two monomer residues. The repeat unit does not include the water molecules eliminated.

尼龙-6,6 的重复单元：(-NH-(CH₂)₆-NH-CO-(CH₂)₄-CO-)ₙ。注意酰胺基的方向；也可以画成 -NH-CO- 连接两个单体残基。重复单元不包括脱去的水分子。

Proteins are natural polyamides (polypeptides) formed from amino acids. The amide links are called peptide bonds. If you see a polyamide question on the exam, treat it like a nylon-type structure unless it is explicitly biological.

蛋白质是由氨基酸形成的天然聚酰胺（多肽）。酰胺键称为肽键。如果在考卷上遇到聚酰胺问题，除非明确是生物型的，否则按尼龙类结构处理。

7. Proteins and Amino Acids | 蛋白质与氨基酸

Proteins are condensation polymers of amino acids. An amino acid contains an amine group (-NH₂) and a carboxylic acid group (-COOH) attached to the same carbon atom. The simplest is glycine (H₂N-CH₂-COOH). In a peptide bond formation, the amine group of one amino acid reacts with the carboxyl group of another, eliminating water and forming -CONH-.

蛋白质是氨基酸的缩合聚合物。氨基酸含有连接在同一碳原子上的氨基 (-NH₂) 和羧酸基 (-COOH)。最简单的是甘氨酸 (H₂N-CH₂-COOH)。在肽键形成过程中，一个氨基酸的氨基与另一个氨基酸的羧基反应，脱去水，形成 -CONH-。

You must be able to draw the dipeptide formed from two given amino acids, showing the peptide link. The backbone has the repeating pattern -NH-Cα-CO- with varied side chains (R groups). Hydrolysis of proteins yields the constituent amino acids; in the lab, this is done by heating with 6 mol dm⁻³ HCl under reflux.

你必须能够画出两个给定氨基酸形成的二肽，显示肽键。主链具有重复模式 -NH-Cα-CO-，侧链 (R 基) 各异。蛋白质水解生成组成氨基酸；实验室中通过用 6 mol dm⁻³ HCl 回流加热来实现。

8. DNA and Nucleotides | DNA 和核苷酸

DNA (deoxyribonucleic acid) is a natural condensation polymer made of nucleotide monomers. Each nucleotide consists of a phosphate group, a deoxyribose sugar, and a nitrogenous base (adenine, thymine, cytosine, or guanine). The polymerisation occurs between the phosphate group of one nucleotide and the sugar of the next, forming a phosphodiester link.

DNA（脱氧核糖核酸）是由核苷酸单体构成的天然缩合聚合物。每个核苷酸由一个磷酸基团、一个脱氧核糖和一个含氮碱基（腺嘌呤、胸腺嘧啶、胞嘧啶或鸟嘌呤）组成。聚合发生在一个核苷酸的磷酸基团与下一个核苷酸的糖之间，形成磷酸二酯键。

The sugar-phosphate backbone is held together by covalent phosphodiester bonds, while the two antiparallel strands of the double helix are held by hydrogen bonds between complementary base pairs: A=T (two H-bonds) and C≡G (three H-bonds). You don’t need to draw the full structure, but you should recognise the condensation polymer aspect: H₂O is eliminated when each sugar-phosphate link forms.

糖-磷酸骨架通过共价磷酸二酯键连接在一起，而双螺旋的两条反平行链则由互补碱基对之间的氢键维系：A=T（两个氢键）和 C≡G（三个氢键）。不需要画出完整结构，但应认识到缩合聚合的特征：每个糖-磷酸键形成时脱去 H₂O。

9. Hydrolysis of Condensation Polymers | 缩合聚合物的水解

Because condensation polymers contain polar functional groups like ester or amide links, they can be broken down by hydrolysis. Acidic or alkaline hydrolysis breaks polyesters back into diol and dicarboxylic acid (or their salts). Polyamides hydrolyse to diamine and dicarboxylic acid under acidic conditions, or to diamine and carboxylate salt under alkaline conditions. Proteins hydrolyse to amino acids; DNA hydrolyses to nucleotides.

由于缩合聚合物含有酯键或酰胺键等极性官能团，它们可以通过水解分解。酸性或碱性水解将聚酯分解回二醇和二羧酸（或其盐）。聚酰胺在酸性条件下水解为二胺和二羧酸，在碱性条件下水解为二胺和羧酸盐。蛋白质水解为氨基酸；DNA 水解为核苷酸。

Exam questions often ask you to write equations for the hydrolysis of a given repeat unit. You must add water (H₂O) across the ester or amide bond, reversing the condensation reaction. For example, hydrolysing a polyester repeat unit with HCl yields the original diol and dicarboxylic acid (or diacid chloride if that was the monomer).

考题常要求写出给定重复单元水解的方程式。你必须在酯键或酰胺键上加成水 (H₂O)，逆转缩合反应。例如，用 HCl 水解某聚酯重复单元，得到原来的二醇和二羧酸（或二酰氯，如果那是单体）。

10. Thermoplastic and Thermosetting Polymers | 热塑性与热固性聚合物

Addition polymers like poly(ethene) and PVC are thermoplastic. They consist of long chains with weak intermolecular forces (London forces or dipole-dipole). Heating softens them because the weak intermolecular forces are overcome; they can be remoulded and recycled. Thermosetting polymers, like Bakelite or vulcanised rubber, have covalent cross-links between chains, making them rigid and heat resistant. They do not soften on heating; instead they char and cannot be remoulded.

像聚乙烯和 PVC 这样的加成聚合物是热塑性的。它们由长链组成，链间有较弱的分子间力（伦敦力或偶极-偶极）。加热使它们软化，因为较弱的分子间力被克服；它们可以重塑和回收。热固性聚合物，如酚醛树脂或硫化橡胶，在链间具有共价交联，使其刚硬且耐热。加热时不会软化，而是焦化，无法重塑。

The distinction is crucial for recycling and applications. Edexcel may ask you to explain why certain polymers can be melted and remoulded while others cannot, linking back to the type of intermolecular or covalent bonds between chains.

这种区别对回收和应用至关重要。Edexcel 可能会要求你解释为什么某些聚合物可以熔融重塑而其他不行，需联系到链间分子间键或共价键的类型。

11. Disposal and Recycling of Polymers | 聚合物的处理与回收

Polyalkenes (addition polymers) are non-biodegradable because their saturated C-C backbone is inert. They persist in the environment, causing long-term pollution. Incineration can recover energy but releases CO₂ and toxic gases like HCl from PVC. Recycling involves melting and remoulding thermoplastics; sorting is a major challenge. Biodegradable polymers like PLA and polyhydroxyalkanoates (PHAs) are broken down by microorganisms, offering a more sustainable option.

聚烯烃（加成聚合物）不可生物降解，因为其饱和的 C-C 主链是惰性的。它们在环境中持久存在，造成长期污染。焚烧可以回收能量，但会释放 CO₂ 和有毒气体如 PVC 产生的 HCl。回收包括熔融和重塑热塑性塑料；分类是一大挑战。可生物降解聚合物如 PLA 和聚羟基烷酸酯 (PHA) 能被微生物分解，提供了更可持续的选择。

Feedstock recycling, where polymers are broken down back into monomers or useful chemicals, is an emerging technology. Condensation polymers can be hydrolysed under controlled conditions, but this is expensive. The exam may present a comprehension question on the environmental impact or life-cycle analysis of polymers; apply your knowledge of structure and bonding here.

原料回收，即将聚合物分解回单体或有用的化学原料，是一种新兴技术。缩合聚合物可在受控条件下水解，但成本很高。考试可能出现关于聚合物环境影响或生命周期分析的理解题；此时要运用结构和键合的知识。

12. Exam Tips and Common Mistakes | 考试技巧与常见错误

Always show extension bonds at both ends of the repeat unit when drawing polymers. They must go through the brackets. For condensation polymers, make sure you include the correct number of carbon atoms from each monomer in the repeat unit; missing a CH₂ group is a common error. When writing equations, balance the number of water molecules eliminated: two monomers form one ester/amide link and eliminate one H₂O, but in a long chain, the number of water molecules per repeat unit depends on the number of functional groups.

绘制聚合物时，务必在重复单元两端显示延伸键。它们必须穿过方括号。对于缩合聚合物，确保在重复单元中包含每个单体正确的碳原子数目；遗漏一个 CH₂ 基团是常见错误。写方程式时，要平衡脱去的水分子数目：两个单体形成一个酯/酰胺键并脱去一个 H₂O，但在长链中，每个重复单元脱去的水分子数取决于官能团数量。

For polypeptide chains, remember that the N-terminus is the free -NH₂ end and the C-terminus is the free -COOH end. When drawing dipeptides, the peptide bond is planar and trans. In naming repeat units, do not confuse the monomer name with the polymer name: poly(ethene) is made from ethene, not ‘polyethene’ as the monomer.

对于多肽链，记住 N 端是游离的 -NH₂ 端，C 端是游离的 -COOH 端。画二肽时，肽键是平面且反式的。在命名重复单元时，不要混淆单体名和聚合物名：聚（乙烯）是由乙烯制成的，单体不是“聚乙烯”。

Finally, in distinguishing addition and condensation polymers, look for the presence of heteroatoms (O, N) in the backbone of the repeat unit. If the backbone contains only carbon, it is likely an addition polymer. If it contains ester or amide links, it is a condensation polymer. This simple rule works for almost all A-Level cases.

最后，在区分加成和缩合聚合物时，查看重复单元主链中是否含有杂原子（O、N）。如果主链只含碳，很可能是加成聚合物。如果含有酯键或酰胺键，则是缩合聚合物。这条简单规则适用于几乎所有 A-Level 情况。

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Polymers: Key Concepts for A-Level Edexcel Chemistry | A-Level Edexcel 化学：聚合物 考点精讲