📚 Polymers Revision for IGCSE CCEA Chemistry: Monomers, Polymerisation and Uses | IGCSE CCEA 化学：聚合物考点精讲（单体、聚合反应与应用）
Polymers are an essential topic in IGCSE CCEA Chemistry, covering macromolecules, polymerisation types, repeating units and real-world applications. This article breaks down the key concepts, equations, structures and examples you need for the exam, from addition and condensation polymerisation to natural polymers, properties, disposal problems and examiner tips.
聚合物是 IGCSE CCEA 化学中的一个重要主题，涵盖大分子、聚合类型、重复单元及实际应用。本文分解了你需要掌握的关键概念、方程、结构与例子，从加成聚合、缩聚到天然聚合物、性质、废弃处理问题以及考官提示。
1. What are Polymers? | 什么是聚合物？
A polymer is a giant molecule made from many repeating units called monomers. The word comes from the Greek: 'poly' means many and 'mer' means part. The monomers are linked together by strong covalent bonds to form long chains, and the relative molecular mass of a polymer may be tens of thousands or more.
聚合物是由许多称为单体的重复单元组成的巨大分子。这个词来自希腊语："Poly" 意为许多，"mer" 意为部分。单体通过强共价键连接形成长链，聚合物的相对分子质量可达数万甚至更大。
Polymers can be natural (such as proteins, starch and cellulose) or synthetic (man-made), such as polythene and nylon. Natural polymers are produced by living organisms, while synthetic polymers are made industrially from chemicals usually obtained from crude oil.
聚合物可以是天然的（如蛋白质、淀粉和纤维素）或合成的（人造的），如聚乙烯和尼龙。天然聚合物由生物体产生，而合成聚合物则由通常来自原油的化学物质在工业上制成。
The properties of a polymer depend on the monomer used, the chain length, and the degree of branching or cross-linking. Long chains with weak forces between them give a flexible, stretchable material, while strong cross-links between chains give a rigid, infusible solid.
聚合物的性质取决于所用单体、链长以及支化或交联的程度。长链之间作用力弱会得到柔软、可拉伸的材料，而链间强交联则得到坚硬、不可熔的固体。
2. Monomers and Repeating Units | 单体与重复单元
arbon double bond, C=C. In condensation polymerisation each monomer must contain at least two reactive functional groups, such as -COOH, -OH or -NH₂.
单体是一种小的活泼分子，可以与许多相同分子结合。在加成聚合中，单体必须含有碳碳双键 C=C。在缩聚中，每个单体必须含有至少两个反应性官能团，如 -COOH、-OH 或 -NH₂。
The repeating unit is the smallest section of the polymer chain that repeats along its whole length. It is written inside brackets with a subscript n after the closing bracket, showing that the unit repeats many times.
重复单元是聚合物链中沿整条链重复的最小片段。它写在方括号内，右括号后加下标 n，表示该单元重复很多次。
- g unit has exactly the same atoms as the monomer, but the C=C becomes a C-C single bond. / 对加成聚合物而言，重复单元的原子组成与单体完全相同，只是 C=C 变成了 C-C 单键。
- For a condensation polymer, the repeating unit has fewer atoms than the two monomers added together, because a small molecule such as water has been lost. / 对缩聚物而言，重复单元的原子数少于两个单体之和，因为失去了像水这样的小分子。
- The empirical formula of an addition polymer is the same as that of its monomer. / 加成聚合物的实验式与其单体相同。
3. Addition Polymerisation | 加成聚合
ing together without the loss of any atoms or small molecules. The double bond opens up and the monomers add to each other to form a saturated backbone of single bonds.
加成聚合涉及不饱和单体（含有碳碳双键 C=C）连接在一起，不丢失任何原子或小分子。双键打开，单体相互加成形成由单键构成的饱和主链。
The general equation can be written as follows, where A represents a substituted ethene molecule. The product is a long-chain polymer, and the repeating unit has the same atoms as the monomer.
通式可写为如下形式，其中 A 代表取代的乙烯分子。产物为长链聚合物，重复单元的原子组成与单体相同。
n A=A → (-A-A-)ₙ
For ethene itself the equation is simpler. Note that all the atoms of the monomer appear in the polymer, so the reaction is an addition reaction and the atom economy is 100%.
对于乙烯本身，方程更简单。注意单体的所有原子都出现在聚合物中，因此这是加成反应，原子经济性为 100%。
n CH₂=CH₂ → (-CH₂-CH₂-)ₙ
High pressure and a catalyst (for example a Ziegler-Natta catalyst or an organic peroxide initiator) are often required for industrial addition polymerisation. The catalyst provides a free-radical or coordination route that allows the chains to grow rapidly under controlled conditions.
工业上的加成聚合通常需要高压和催化剂（例如齐格勒-纳塔催化剂或有机过氧化物引发剂）。催化剂提供自由基或配位途径，使链在受控条件下快速增长。
4. Examples of Addition Polymers | 加成聚合物的例子
The table below summarises common addition polymers, their monomers, repeating units and typical uses. Learn at least polythene, polypropene, PVC and PTFE by name, because naming and structure questions are very common in CCEA papers.
下表总结了常见的加成聚合物、它们的单体、重复单元和典型用途。至少要记住聚乙烯、聚丙烯、PVC 和 PTFE 的名称，因为命名和结构题在 CCEA 试卷中非常常见。
| Monomer 单体 | Polymer 聚合物 | Repeating unit 重复单元 | Uses 用途 |
| ethene 乙烯 | poly(ethene) 聚乙烯 | (-CH₂-CH₂-)ₙ | bags, bottles 塑料袋、瓶子 |
| propene 丙烯 | poly(propene) 聚丙烯 | (-CH₂-CH(CH₃)-)ₙ | ropes, carpets 绳索、地毯 |
| chloroethene 氯乙烯 | poly(chloroethene) PVC 聚氯乙烯 | (-CH₂-CHCl-)ₙ | pipes, window frames 管道、窗框 |
| tetrafluoroethene 四氟乙烯 | PTFE 聚四氟乙烯 | (-CF₂-CF₂-)ₙ | non-stick pans 不粘锅涂层 |
| phenylethene (styrene) 苯乙烯 | poly(styrene) 聚苯乙烯 | (-CH₂-CH(C₆H₅)-)ₙ | packaging, cups 包装、杯子 |
5. Drawing and Naming the Repeating Unit | 绘制与命名重复单元
Exam questions often give you a monomer and ask for the repeating unit, or give a polymer chain and ask you to identify the monomer. Work through the following steps every time, and you will rarely lose marks.
考试题常给出单体要求写出重复单元，或给出聚合物链要求识别单体。每次都按以下步骤操作，你就很少丢分。
- Step 1: Write the monomer with its C=C shown clearly. / 第一步：写出单体，清楚显示 C=C。
- Change the C=C into a single C-C bond and place brackets around the two-carbon section. / 第二步：把 C=C 改为 C-C 单键，并用括号把这两个碳的片段括起来。
- Step 3: Add the side groups (such as -CH₃, -Cl, -F, -C₆H₅) on the correct carbon atoms, keeping the same order as in the monomer. / 第三步：在正确的碳原子上加上侧基（如 -CH₃、-Cl、-F、-C₆H₅），顺序与单体一致。
- Step 4: Write the subscript n outside the closing bracket. / 第四步：在右括号外写下标 n。
- Step 5: Check the bonds - the two ends of the repeating unit must each have a free bond to join the next unit. / 第五步：检查键——重复单元两端必须各有一个自由键以连接下一个单元。
The exam also expects the common names in the form poly(ethene), poly(chloroethene) and so on. Never write 'polyethene' with an incorrect prefix, and always name the polymer after the monomer it came from.
考试还要求使用 poly(ethene)、poly(chloroethene) 这类常见命名形式。不要写错前缀，并且始终根据单体来命名聚合物。
6. Condensation Polymerisation | 缩聚
Condensation polymerisation occurs when two different monomers, each with at least two functional groups, react together and a small molecule is eliminated at every link. The small molecule is usually water, but it can also be hydrogen chloride or methanol.
缩聚发生在两种不同的单体之间，每种单体至少含有两个官能团，反应时在每个连接处消去一个小分子。这个小分子通常是水，也可能是氯化氢或甲醇。
Because atoms are lost, the repeating unit of a condensation polymer is not simply two monomers joined together. You must remove the atoms of the small molecule from your structure when you draw it.
由于有原子丢失，缩聚物的重复单元并不只是两个单体简单相连。绘图时必须从结构中减去小分子的原子。
n HOOC-R-COOH + n HO-R'-OH → (-CO-R-CO-O-R'-O-)ₙ + 2n H₂O
n HOOC-R-COOH + n H₂N-R'-NH₂ → (-CO-R-CO-NH-R'-NH-)ₙ + 2n H₂O
Notice that the two types of condensation polymer differ only in the linkage formed: an ester link (-CO-O-) or an amide link (-CO-NH-). This linkage is the key feature that examiners look for in your diagram.
注意两种缩聚物只在形成的连接键上不同：酯键 (-CO-O-) 或酰胺键 (-CO-NH-)。这个连接键是考官在你的图中寻找的关键特征。
7. Polyesters and Polyamides | 聚酯与聚酰胺
Polyesters are made from a dicarboxylic acid and a diol (a molecule with two -OH groups). Terylene, also called PET, is made from benzene-1,4-dicarboxylic acid and ethane-1,2-diol, and it is widely used for clothing fibres and drinks bottles.
聚酯由二羧酸和二醇（含两个 -OH 的分子）制得。特丽纶（又称 PET）由苯-1,4-二甲酸和乙烷-1,2-二醇制得，广泛用于衣物纤维和饮料瓶。
Polyamides are made from a dicarboxylic acid and a diamine (a molecule with two -NH₂ groups). Nylon-6,6 is made from hexanedioic acid and 1,6-diaminohexane, and it is used for ropes, fabrics and parachutes because of its strength and elasticity.
聚酰胺由二羧酸和二胺（含两个 -NH₂ 的分子）制得。尼龙-6,6 由己二酸和 1,6-二氨基己烷制得，因其强度和弹性被用于绳索、织物和降落伞。
A key industrial advantage of condensation polymers is that the small molecule released can be removed, driving the reaction forward. Hydrogen bonding between amide links also makes nylon strong, whereas polyester fibres are often blended with cotton to improve comfort.
缩聚物在工业上的一个重要优势是释放的小分子可以被除去，从而推动反应正向进行。酰胺键之间的氢键还使尼龙结实，而聚酯纤维常与棉混纺以提高舒适度。
8. Natural Polymers | 天然聚合物
Proteins are natural condensation polymers of amino acids joined by peptide (amide) links. When a protein is hydrolysed with acid or enzymes, it breaks down into its constituent amino acids, which can be separated by chromatography.
蛋白质是由氨基酸通过肽键（酰胺键）连接的天然缩聚物。当蛋白质用酸或酶水解时，会分解为其组成氨基酸，可用色谱法分离。
Starch and cellulose are both condensation polymers of glucose. Starch is used as an energy store in plants, while cellulose forms cell walls. They have the same monomer but different linkages, which is why humans can digest starch but not cellulose.
淀粉和纤维素都是葡萄糖的缩聚物。淀粉在植物中用作能量储存，而纤维素构成细胞壁。它们单体相同但连接方式不同，这就是人能消化淀粉却不能消化纤维素的原因。
- Natural rubber is an addition polymer of 2-methylbuta-1,3-diene (isoprene). / 天然橡胶是 2-甲基丁-1,3-二烯（异戊二烯）的加成聚合物。
- DNA is a condensation polymer of nucleotides and stores genetic information. / DNA 是核苷酸的缩聚物，储存遗传信息。
- Vulcanisation uses sulfur to form cross-links between rubber chains, making the rubber harder and more durable. / 硫化用硫在橡胶链之间形成交联，使橡胶更硬更耐用。
9. Properties and Uses of Polymers | 聚合物的性质与用途
The physical properties of a polymer are controlled mainly by the strength of the forces between the chains, not by the covalent bonds inside each chain. Long, straight chains pack closely and have strong intermolecular forces, giving a high melting point and high tensile strength.
聚合物的物理性质主要由链间作用力的强弱决定，而不是由链内共价键决定。长而直的链排列紧密，分子间作用力强，因而熔点和抗拉强度都高。
Branched chains cannot pack as closely, so the forces between them are weaker. This is why low-density polythene, which is more branched, is softer and more flexible than high-density polythene, which has straighter chains.
支化的链不能紧密排列，因此链间作用力较弱。这就是为什么支化较多的低密度聚乙烯比链更直的高密度聚乙烯更柔软、更易弯曲。
| Type 类型 | Structure 结构 | Behaviour on heating 受热行为 | Example 例子 |
| thermosoftening 热塑性 | long chains, weak forces between them 长链，链间力弱 | softens and can be remoulded 软化且可重塑 | polythene, PVC 聚乙烯、PVC |
| thermosetting 热固性 | covalent cross-links between chains 链间共价交联 | does not soften, chars on strong heating 不软化，强热时碳化 | urea-methanal, vulcanised rubber 脲醛树脂、硫化橡胶 |
10. Branching, Cross-linking and Crystallinity | 支化、交联与结晶度
Cross-links are strong covalent bonds that join different polymer chains together. A lightly cross-linked polymer is still flexible, such as vulcanised rubber, whereas a heavily cross-linked polymer is rigid and cannot be melted or reshaped.
交联是把不同聚合物链连接在一起的强共价键。轻度交联的聚合物仍具柔性，如硫化橡胶；而重度交联的聚合物则坚硬，不能熔化或重塑。
Crystallinity refers to regions where chains line up in an ordered pattern. More crystalline regions mean a denser, stronger and less transparent material, which is why high-density polythene is used for rigid bottles rather than thin films.
结晶度指链以有序方式排列的区域。结晶区越多，材料越致密、越强，透明度越低，这就是高密度聚乙烯用于硬质瓶而非薄膜的原因。
Plasticisers are small molecules added between polymer chains to reduce the forces between them, making the plastic softer and more flexible. This is how rigid PVC is turned into the flexible PVC used for electrical cable insulation.
增塑剂是加在聚合物链之间的小分子，用来削弱链间作用力，使塑料更软更柔韧。刚性 PVC 就是这样变成用于电线绝缘层的软 PVC。
11. Disposal, Recycling and Environmental Issues | 处理、回收与环境问题
Most synthetic polymers are non-biodegradable because the strong C-C backbone is not attacked by the enzymes produced by microorganisms. They therefore remain in landfill sites for many decades and can harm wildlife if they enter rivers and oceans.
大多数合成聚合物不可生物降解，因为微生物产生的酶无法破坏牢固的 C-C 主链。因此它们会在垃圾填埋场存在数十年，若进入河流和海洋还会危害野生动物。
Burning polymers releases carbon dioxide, a greenhouse gas, and can produce toxic gases. Burning PVC is especially problematic because it can release hydrogen chloride and other harmful substances.
燃烧聚合物会释放二氧化碳这种温室气体，还可能产生有毒气体。燃烧 PVC 尤其有问题，因为它可能释放氯化氢和其他有害物质。
- Recycling melts and remoulds the plastic, saving crude oil but requiring sorting of different polymer types. / 回收是熔化并重塑塑料，可节省原油，但需要对不同种类塑料进行分类。
- Feedstock recycling breaks polymers down chemically into useful small molecules and monomers. / 原料回收通过化学方法把聚合物分解为有用的小分子和单体。
- Biodegradable polymers, such as PLA made from plant starch, are broken down by microorganisms. / 可生物降解聚合物，如由植物淀粉制成的 PLA，可被微生物分解。
- Reducing use, reusing bags and choosing refillable containers are the most effective ways to cut plastic waste. / 减少使用、重复使用塑料袋、选择可再填充容器是减少塑料废弃物最有效的方法。
12. Exam Tips and Common Mistakes | 考试技巧与常见错误
Read the command word carefully. If a question says 'draw the repeating unit', you must show brackets and the subscript n; if it says 'state the monomer', a name or displayed formula is enough.
仔细阅读指令词。如果题目要求 "draw the repeating unit"（画出重复单元），你必须画出括号和下标 n；如果要求 "state the monomer"（写出单体），给出名称或结构式即可。
C inside the repeating unit, forgetting the brackets or the n, drawing termination bonds incorrectly, and confusing ester links with amide links in condensation polymers.
常见错误包括：在重复单元中保留了 C=C、忘记括号或 n、封端键画错，以及在缩聚物中把酯键与酰胺键混淆。
- Always check atom counts when writing condensation equations - the lost water molecules must balance. / 写缩聚方程时务必核对原子数——失去的水分子必须配平。
- Link polymer properties to structure: chain length, branching, cross-linking and intermolecular forces. / 把聚合物性质与结构联系起来：链长、支化、交联和分子间作用力。
- When explaining uses, give a property first and then the reason, for example 'PTFE is used for non-stick pans because it is unreactive and has a very low friction surface'. / 解释用途时先给性质再给理由，例如 "PTFE 用于不粘锅，因为它不活泼且表面摩擦系数很低"。
- Practise drawing repeating units for at least six common polymers until it becomes automatic. / 至少练习画出六种常见聚合物的重复单元，直到成为条件反射。
With careful structure drawing and a clear grasp of the two polymerisation mechanisms, polymers become one of the most reliable sources of marks in the CCEA IGCSE Chemistry paper.
只要结构画得准确，并清楚掌握两种聚合机理，聚合物就会成为 CCEA IGCSE 化学试卷中最稳定的得分点之一。
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