📚 GCSE AQA Chemistry: Polymers – Key Points Revision | GCSE AQA 化学：聚合物 考点精讲
Polymers are large molecules formed by joining many small monomer units together. In AQA GCSE Chemistry you need to understand two main types of polymerisation - addition and condensation. You should be able to identify monomers, draw repeating units, explain the differences between thermosoftening and thermosetting materials, and discuss the environmental issues relating to plastics.
聚合物是由许多小单体通过化学键连接而成的大分子。在 AQA GCSE 化学中，你需要掌握两类主要的聚合反应：加成聚合和缩合聚合。你应当能够识别单体、绘制重复单元、解释热塑性和热固性材料的区别，并讨论与塑料相关的环境问题。
1. What Are Polymers? | 什么是聚合物？
A polymer is a very large molecule (a macromolecule) built from many small molecules called monomers, joined together by covalent bonds. The reaction that links them is called polymerisation. Polymers can be natural - , such as DNA, proteins, and starch and cellulose are all natural polymers - or synthetic (man-made), such as poly(ethene), nylon and PET. The physical properties of a polymer depend on the atoms in the monomer, the length of the chains and the forces between the chains.
聚合物是由许多称为单体的小分子通过共价键连接而成的大分子（高分子）。把它们连接起来的反应叫做聚合反应。聚合物可以是天然的——DNA、蛋白质、淀粉和纤维素都是天然聚合物——也可以是合成的（人造的），如聚乙烯、尼龙和 PET。聚合物的性质取决于单体中的原子、链的长度以及链与链之间的作用力。
Key vocabulary you must use accurately: monomer (the small molecule that repeats), polymer (the long chain), repeating unit (the section of the chain that repeats), and polymerisation (the process of joining monomers).
必须准确使用的关键词汇：单体（重复出现的小分子）、聚合物（长链）、重复单元（链中重复出现的那一段）以及聚合反应（连接单体的过程）。
2. Addition Polymerisation | 加成聚合反应
Under high pressure and in the presence of a catalyst, the double bond opens and each monomer bonds to two neighbours, producing a long saturated carbon backbone. No other product is formed: every atom of the monomer ends up in the polymer. This is why the empirical formula of an addition polymer is exactly the same as the empirical formula of its monomer.
加成聚合反应发生在含有碳碳双键（C=C）的单体之间。在高压和催化剂存在的条件下，双键打开，每个单体与相邻的两个单体成键，形成一条长的饱和碳链主链。反应不生成其他产物：单体的每一个原子都进入聚合物中。这正是加成聚合物的经验式与其单体的经验式完全相同的原因。
n CH₂=CH₂ → –[CH₂–CH₂]ₙ–
nit contains the same atoms as the monomer, except that the C=C double bond has become a C– he two bonds drawn through the brackets are the bonds to the neighbouring repeating units.
一般方程式为：n 单体 → 聚合物，其中 n 是一个非常大的数。重复单元与单体含有相同的原子，只是 C=C 双键变成了 C–C 单键。穿过方括号的两条键表示与相邻重复单元相连的键。
- Only one product is formed - the polymer.
- The reaction is an addition reaction, so nothing is lost.
- The polymer is saturated even though the monomer was unsaturated.
- 只生成一种产物——聚合物。
- 该反应属于加成反应，因此没有任何原子被失去。
- 单体是不饱和的，但生成的聚合物是饱和的。
3. Examples of Addition Polymers | 加成聚合物实例
The table below summarises the common addition polymers required by for the AQA GCSE specification. Learn the monomer, the repeating unit and one typical use for each.
下表总结了 AQA GCSE 考纲要求掌握的常见加成聚合物。请记住每种聚合物的单体、重复单元以及一个典型用途。
| Monomer 单体 | Polymer 聚合物 | Repeating unit 重复单元 | Typical use 典型用途 |
| Ethene CH₂=CH₂ | Poly(ethene) | –[CH₂–CH₂]ₙ– | bags, bottles, cable insulation |
| Propene CH₂=CHCH₃ | Poly(propene) | –[CH₂–CH(CH₃)]ₙ– | carpets, ropes, food containers |
| Chloroethene CH₂=CHCl | Poly(chloroethene) PVC | –[CH₂–CHCl]ₙ– | window frames, pipes, flooring |
| Tetrafluoroethene CF₂=CF₂ | PTFE | –[CF₂–CF₂]ₙ– | non-stick coatings, bearings |
Notice the naming pattern: the polymer name is simply "poly" plus the name of the monomer in brackets, for example poly(propene). If a question asks you to name the polymer formed from a given alkene, this rule almost always gives the right answer.
注意命名规律：聚合物名称就是 "poly" 加上括号里的单体名称，例如 poly(propene)。如果题目要求你为某种烯烃生成的聚合物命名，这条规律几乎总是适用的。
4. Drawing Repeating Units Correctly | 如何正确绘制重复单元
Drawing the repeating unit is a very common exam question, and marks are awarded for specific features. Get into the habit of checking every one of the points below before you move on.
绘制重复单元是极常见的考题，评分是针对具体特征给分的。养成在继续答题前逐条检查下面各点的习惯。
- Draw the repeating unit inside square brackets, with n written after the closing bracket.
- Draw two free bonds passing through the brackets - one on the left, one on the right - to show how the units link.
- Show every atom of the monomer, including side groups such as CH₃, Cl or F.
- Turn the C=C double bond into a C–C single bond; do not keep the double bond inside the chain.
- Do not add or remove any atoms - addition polymers keep all the monomer atoms.
- 把重复单元画在方括号内，并在右括号后面写上 n。
- 画出两条穿过方括号的游离键——左边一条、右边一条——表示单元之间如何连接。
- 画出单体的每一个原子，包括 CH₃、Cl、F 等侧基。
- 把 C=C 双键改为 C–C 单键；不要把双键保留在链中。
- 不要增加或减少任何原子——加成聚合物保留了单体的全部原子。
A quick check: count the atoms in your repeating unit. For poly(propene) the repeating unit –[CH₂–CH(CH₃)]ₙ– contains C₃H₆, exactly the same as one molecule of propene, C₃H₆. If the counts match the monomer, you have almost certainly drawn it correctly.
快速检查法：数一数重复单元中的原子。聚丙烯的重复单元 –[CH₂–CH(CH₃)]ₙ– 含有 C₃H₆，与一个丙烯分子 C₃H₆ 完全一致。如果数目与单体相符，你几乎肯定画对了。
5. Condensation Polymerisation | 缩合聚合反应
Condensation polymerisation involves two different monomers, each of which has two functional groups. When the two functional groups react, a small molecule (usually water) is eliminated, and the monomers become linked. Because each monomer has two reactive ends, the process continues in both directions to build a long chain.
缩合聚合反应涉及两种不同的单体，每种单体带有两个官能团。当两个官能团发生反应时，会脱去一个小分子（通常是水），单体随之连接起来。由于每种单体都有两个反应端，反应可以向两个方向继续，从而形成长链。
dicarboxylic acid + diol → polyester + water
dicarboxylic acid + diamine → polyamide + water
The three functional groups you need to recognise are the carboxylic acid group –COOH, the alcohol group –OH and the amine group –NH₂. The word "di" in diol, dicarboxylic acid and diamine means there are two of these groups on each monomer, which is essential for forming a chain rather than a simple pair.
你需要识别的三个官能团是羧基 –COOH、醇羟基 –OH 和氨基 –NH₂。diol（二醇）、dicarboxylic acid（二羧酸）和 diamine（二胺）中的 "di" 表示每个单体上有两个这样的基团，这是形成长链而不是只连成一对的关键。
6. Polyesters and Polyamides | 聚酯与聚酰胺
Polyesters are made from a dicarboxylic acid and a diol. The link formed is an ester link, –COO–. A familiar example is PET (often called terylene), made from benzene-1,4-dicarboxylic acid and ethane-1,2-diol, and used for drinks bottles and clothing fibres.
聚酯由二羧酸和二醇制得，形成的连接是酯键 –COO–。一个熟悉的例子是 PET（常称为涤纶/特丽纶），由苯-1,4-二甲酸和乙-1,2-二醇制得，用于饮料瓶和衣物纤维。
Polyamides are made from a dicarboxylic acid and a diamine. The link formed is an amide link, –CONH–. Nylon is a polyamide made from hexanedioic acid and hexane-1,6-diamine, and is used for clothing, ropes and carpets because of its strength and elasticity.
聚酰胺由二羧酸和二胺制得，形成的连接是酰胺键 –CONH–。尼龙是一种聚酰胺，由己二酸和己-1,6-二胺制得，因其强度和弹性而用于衣物、绳索和地毯。
Exam skill: if you are given a section of a polymer chain and asked to deduce the monomers, look for the ester link or amide link, then add the elements of water back across it. The –COO– link came from –COOH plus –OH; the –CONH– link came from –COOH plus –NH₂.
答题技巧：如果题目给出聚合物链的一段并要求推断单体，先找出酯键或酰胺键，再把水的元素"加回去"。–COO– 键来自 –COOH 加 –OH；–CONH– 键来自 –COOH 加 –NH₂。
7. Natural Polymers | 天然聚合物
Not all polymers are made in factories. Proteins, starch, cellulose and DNA are all natural polymers produced by living organisms, and most of them are formed by condensation polymerisation.
并非所有聚合物都是在工厂里制造的。蛋白质、淀粉、纤维素和 DNA 都是生物体产生的天然聚合物，其中大多数通过缩合聚合形成。
- Proteins are polyamides made from amino acids. Each amino acid has an –NH₂ group and a –COOH group, so they link by amide (peptide) bonds, losing water each time.
- Starch and cellulose are made from glucose molecules joined by condensation, again releasing water.
- DNA is a polymer built from repeating nucleotide units and carries genetic information.
- 蛋白质是由氨基酸构成的聚酰胺。每个氨基酸都有一个 –NH₂ 和一个 –COOH，因此它们通过酰胺（肽）键连接，每次脱去一个水分子。
- 淀粉和纤维素由葡萄糖分子通过缩合连接而成，同样会释放水。
- DNA 是由重复的核苷酸单元构成的大分子聚合物，携带着遗传信息。
Recognising that proteins are polyamides and that starch is a condensation polymer helps you see that the chemistry you learn in the lab is the same chemistry that happens in your cells.
认识到蛋白质属于聚酰胺、淀粉属于缩合聚合物，有助于理解实验室里学到的化学与细胞内发生的化学本质上是同一套原理。
8. Thermosoftening (Thermoplastic) Polymers | 热塑性聚合物
Thermosoftening polymers consist of individual long-chain molecules that are tangled together but not joined by covalent bonds. The only forces between the chains are weak intermolecular forces. When the polymer is heated, these weak forces are easily overcome, so the chains can slide over one another and the material softens. On cooling it becomes rigid again, which means it can be melted and remoulded many times.
热塑性聚合物由相互缠绕但不以共价键相连的独立长链分子组成。链与链之间只有较弱的作用力。加热时，这些弱作用力很容易被克服，链可以相互滑动，材料随之变软。冷却后它重新变硬，因此可以反复熔融和重新塑形。
Typical examples include poly(ethene) used for carrier bags and bottles, and poly(propene) used for containers and carpets. These materials are easy to recycle by melting and reshaping.
典型例子包括用于购物袋和瓶子的聚乙烯，以及用于容器和地毯的聚丙烯。这类材料易于通过熔融重塑进行回收。
9. Thermosetting Polymers | 热固性聚合物
Thermosetting polymers have strong covalent cross-links between the polymer chains, forming a rigid three-dimensional network. Because these cross-links are covalent bonds, heating does not allow the chains to slide. The material does not soften on heating; instead it eventually chars or burns. Thermosetting polymers are hard, strong and rigid, but they cannot be remoulded.
热固性聚合物的链与链之间存在强的共价交联，形成刚性的三维网络。由于这些交联是共价键，加热也不能让链滑动。材料受热不会变软，反而最终会碳化或燃烧。热固性聚合物坚硬、强度高、刚性强，但无法重新塑形。
| Feature 特征 | Thermosoftening 热塑性 | Thermosetting 热固性 |
| Forces between chains | weak intermolecular forces | strong covalent cross-links |
| Effect of heating | softens, can be remoulded | does not soften, chars |
| Typical example | poly(ethene), poly(propene) | cured resins, vulcanised rubber |
Vulcanised rubber is a useful example: sulfur atoms form cross-links between the natural rubber chains, which is why tyres stay rigid when they get hot rather than melting.
硫化橡胶是一个有用的例子：硫原子在天然橡胶链之间形成交联，这就是轮胎发热时仍然保持刚性而不会熔化的原因。
10. Environmental Issues: Plastics and Disposal | 环境问题：塑料与处理
Most synthetic polymers are not biodegradable, meaning microorganisms cannot break them down. Waste plastic therefore persists in landfill and in the environment for a very long time. Plastic in the ocean breaks into microplastics, which are eaten by fish and other wildlife and can enter the food chain. Discarded plastic also traps and injures animals.
大多数合成聚合物不可生物降解，即微生物无法将其分解。因此，废弃塑料会在垃圾填埋场和环境中长期存在。海洋中的塑料会破碎成微塑料，被鱼类和其他野生动物吞食，并可能进入食物链。被丢弃的塑料还会缠绕并伤害动物。
- Burning plastics releases carbon dioxide, a greenhouse gas. Burning PVC also releases hydrogen chloride, HCl, which is toxic and contributes to acid rain.
- Mechanical recycling means sorting, melting and remoulding the plastic. It only works well for thermosoftening polymers.
- Feedstock recycling breaks the polymer back down into its monomers, which can then be used to make new plastic.
- Reducing, reusing and using biodegradable alternatives such as polylactic acid (PLA) made from plant starch, all reduce the problem.
- 焚烧塑料会释放二氧化碳，这是一种温室气体。焚烧 PVC 还会释放氯化氢 HCl，它有毒并会加剧酸雨。
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