📚 Tackling Questions on Addition Polymers | 攻克加成聚合物考题
Addition polymers are one of the most frequently assessed organic chemistry topics in Cambridge A-Level Chemistry. Exam questions usually ask you to draw repeat units, deduce monomers, write polymerisation equations, or link polymer properties to their uses. This article gives a systematic method for tackling these questions accurately and quickly.
加成聚合物是剑桥 A-Level 化学有机部分的高频考点之一。考题通常要求绘制重复单元、反推单体、书写聚合方程式，或将聚合物性质与用途联系起来。本文提供一套系统方法，帮助你准确、快速地解答此类题目。
1. Core Chemistry: What Addition Polymerisation Means | 核心化学：加成聚合的含义
Addition polymerisation is the reaction in which many small unsaturated monomer molecules, usually alkenes or substituted alkenes, join together by opening their carbon-carbon double bonds. Each C=C bond becomes two new single C–C bonds, so no atoms are lost and no small molecule is eliminated.
加成聚合是指许多不饱和的小分子单体（通常是烯烃或取代烯烃）通过打开碳碳双键而连接在一起的反应。每一个 C=C 双键变成两个新的 C–C 单键，因此没有原子损失，也不会脱去小分子。
The only product is the polymer. The repeat unit has the same atoms as the monomer, except that the double bond has become a single bond. For example, poly(ethene) has the same carbon-to-hydrogen ratio as ethene.
该反应的唯一产物是聚合物。重复单元与单体含有相同的原子，只是双键变成了单键。例如，聚(乙烯)与乙烯具有相同的碳氢比例。
n CH₂=CH₂ → [–CH₂–CH₂–]ₙ
In this equation, the subscript n outside the bracket shows that many repeating units are linked together. The open bonds at each end indicate that the chain continues in both directions.
在该方程中，方括号外的下标 n 表示许多重复单元连接在一起。两端开口的化学键表示分子链向两个方向继续延伸。
2. Common Addition Polymers You Must Know | 必须掌握的常见加成聚合物
Cambridge questions often expect you to recognise common addition polymers, their monomers, and their typical uses. The table below summarises the most important examples.
剑桥考试常要求你识别常见的加成聚合物、对应的单体及其典型用途。下表总结了最重要的例子。
| Monomer | 单体 | Polymer | 聚合物 | Typical use | 典型用途 |
|---|---|---|
| Ethene, CH₂=CH₂ | Poly(ethene) | 聚(乙烯) | Plastic bags, bottles |
| Propene, CH₂=CHCH₃ | Poly(propene) | 聚(丙烯) | Ropes, food containers |
| Chloroethene, CH₂=CHCl | Poly(chloroethene), PVC | 聚(氯乙烯) | Pipes, window frames |
| Styrene, C₆H₅CH=CH₂ | Polystyrene | 聚苯乙烯 | Packaging, insulation |
| Tetrafluoroethene, CF₂=CF₂ | Poly(tetrafluoroethene), PTFE | 聚四氟乙烯 | Non-stick coatings, bearings |
You should be able to write both the monomer structure and the repeat unit structure for each of these polymers. In particular, make sure the side group is drawn on the correct carbon atom.
你应能写出上述每种聚合物的单体结构和重复单元结构。尤其要确保侧基画在正确的碳原子上。
3. Drawing a Repeat Unit from a Given Monomer | 由给定单体绘制重复单元
A repeat unit is the smallest group of atoms that repeats along the polymer chain. When you draw it, show the two carbon atoms that were originally in the double bond linked by a single bond. Enclose the repeat unit in square brackets and place the subscript n outside.
重复单元是沿聚合物链重复出现的最小原子团。绘制时，应将原来形成双键的两个碳原子用单键连接。将重复单元放在方括号内，并在括号外标出下标 n。
The side groups from the monomer stay attached to the same carbon atoms. There must be no double bond inside the repeat unit because the C=C has been used to link monomers. The open bonds at the ends are shown crossing the brackets.
单体上的侧基保留在原来的碳原子上。重复单元内部不能出现双键，因为 C=C 已用于连接单体。两端开口的化学键要画成穿过方括号。
- Step 1: Identify the C=C bond in the monomer.
中文：确定单体中的 C=C 双键。 - Step 2: Replace the double bond with a single C–C bond.
中文：将双键改为 C–C 单键。 - Step 3: Draw the two carbon atoms with their attached atoms or groups exactly as in the monomer.
中文：按照单体原样画出两个碳原子及其连接的原子或基团。 - Step 4: Put the unit in square brackets and write n outside.
中文：将单元放入方括号，并在括号外写 n。
For example, the repeat unit of poly(propene) is written as [–CH₂–CH(CH₃)–]ₙ. Notice that the methyl group is attached to the second carbon, not to the first.
例如，聚(丙烯)的重复单元写作 [–CH₂–CH(CH₃)–]ₙ。注意甲基连接在第二个碳原子上，而不是第一个。
4. Deducing the Monomer from a Polymer Structure | 由聚合物结构反推单体
This is the reverse skill and is very common in exams. First, identify the repeat unit by looking for the repeating pattern along the chain. Remove the brackets and the subscript n, then insert a double bond between the two carbon atoms that were joined by a single bond in the repeat unit.
这是反向推断技能，在考试中非常常见。首先，通过观察链上的重复模式确定重复单元。去掉方括号和下标 n，然后在重复单元中由单键连接的两个碳原子之间插入双键。
For example, given the repeat unit [–CH₂–CHCl–]ₙ, the two carbon atoms are adjacent. Replace the single C–C bond by a double bond. The monomer is therefore chloroethene, CH₂=CHCl.
例如，已知重复单元 [–CH₂–CHCl–]ₙ，两个碳原子相邻。将 C–C 单键改为双键，得到的单体就是氯乙烯 CH₂=CHCl。
A common error is to forget to restore the double bond and write a saturated alkane instead of an alkene. Always check that your final monomer contains one C=C bond.
一个常见错误是忘记恢复双键，写出饱和烷烃而不是烯烃。一定要检查最终的单体是否含有一个 C=C 双键。
5. Naming Addition Polymers Correctly | 正确命名加成聚合物
To name an addition polymer, write the word poly followed by the monomer name in brackets. If the monomer is substituted, keep the monomer name unchanged inside the brackets. For example, chloroethene gives poly(chloroethene), which is commonly known as PVC.
命名加成聚合物时，先写 poly，再将单体名称放在括号中。如果单体有取代基，括号内的单体名称保持不变。例如，氯乙烯生成 poly(chloroethene)，通常称为 PVC。
Do not write polyethene as polythene unless the question specifically uses that industrial name. In Cambridge answers, poly(ethene) is preferred because it clearly identifies the monomer.
除非题目特别使用工业名称，否则不要把 poly(ethene) 写成 polythene。在剑桥考试答案中，优先使用 poly(ethene)，因为它能清楚地标明单体。
When writing a polymerisation equation, show the monomer on the left, the repeat unit in brackets with n on the right, and keep all atoms balanced. No small molecule such as H₂O or HCl appears on the right-hand side.
书写聚合方程式时，左侧写单体，右侧写带 n 的方括号重复单元，并保持所有原子配平。右侧不会出现 H₂O 或 HCl 等小分子。
n CH₂=CHCl → [–CH₂–CHCl–]ₙ
6. Relating Structure to Properties and Uses | 结构与性质和用途的关联
Addition polymers are typically saturated carbon chains. The chains are held together by weak intermolecular forces, so many addition polymers are thermoplastics: they soften when heated and harden when cooled. This property makes them easy to shape and recycle.
加成聚合物通常是饱和碳链。分子链之间依靠较弱的分子间作用力结合，因此许多加成聚合物是热塑性塑料：受热变软，冷却变硬。这一性质使它们易于成型和回收。
PTFE has very strong C–F bonds and a highly regular chain structure. This gives it high chemical inertness, low friction, and excellent heat resistance, making it suitable for non-stick pan coatings and laboratory equipment.
聚四氟乙烯具有非常强的 C–F 键和高度规整的链结构。这使其具有很高的化学惰性、低摩擦性和优异的耐热性，因此适用于不粘锅涂层和实验室设备。
PVC is relatively rigid because the polar C–Cl bonds increase intermolecular attraction between chains. However, adding plasticisers reduces these attractions and makes the material more flexible, which is useful for floor coverings and cable insulation.
聚氯乙烯相对较硬，因为极性的 C–Cl 键增强了分子链间的吸引力。然而，加入增塑剂会减弱这些吸引力，使材料更柔软，可用于地板覆盖层和电缆绝缘层。
7. Industrial Conditions for Addition Polymerisation | 加成聚合的工业条件
In industry, addition polymerisation of ethene typically requires high pressure, an elevated temperature, and a catalyst. The exact conditions depend on the type of poly(ethene) being produced; high-density poly(ethene) uses a Ziegler-Natta catalyst at relatively low pressure, while low-density poly(ethene) uses high pressure and a radical initiator.
在工业上，乙烯的加成聚合通常需要高压、升温和催化剂。具体条件取决于所生产聚乙烯的类型：高密度聚乙烯使用 Ziegler-Natta 催化剂，在相对较低的压力下生产；低密度聚乙烯则使用高压和自由基引发剂。
You are not usually required to memorise every industrial detail, but you should understand why a catalyst is used: it speeds up the reaction and often controls the chain length or branching, which affects the polymer’s properties.
通常不要求记忆所有工业细节，但应理解使用催化剂的原因：它能加快反应，并且往往控制链长或支化程度，从而影响聚合物的性能。
8. Environmental Issues and Recycling | 环境问题与回收利用
Most addition polymers are non-biodegradable because the saturated carbon-carbon backbone is chemically unreactive. Microorganisms lack enzymes that can break the strong C–C bonds quickly, so waste polymers persist in landfill for many decades.
大多数加成聚合物不可生物降解，因为饱和的碳碳主链化学性质稳定。微生物缺少能快速断裂强 C–C 键的酶，因此废塑料会在垃圾填埋场中存留数十年。
Incineration can release useful energy but may also produce toxic gases. For example, burning PVC releases hydrogen chloride, which contributes to acid rain. Exam answers should therefore show balanced evaluation rather than simply saying that incineration is bad.
焚烧可以释放有用能量，但也可能产生有毒气体。例如，燃烧聚氯乙烯会释放氯化氢，导致酸雨。因此，考试答案应体现辩证评价，而不是简单地说焚烧有害。
Recycling involves sorting, shredding, melting, and remoulding. Some polymers can also be cracked back into monomers, but this requires high energy. In exam questions, compare different disposal methods using environmental and economic criteria.
回收利用包括分选、破碎、熔融和重新成型。有些聚合物还可以裂解回单体，但这需要很高的能量。在考试题中，应使用环境和经济标准比较不同的废弃处理方法。
9. Worked Example 1: Drawing a Repeat Unit | 范例 1：绘制重复单元
Question: Draw the repeat unit of poly(phenylethene), also known as polystyrene. Show the side group clearly.
中文题目：画出聚苯乙烯的重复单元，并清楚地标出侧基。
Answer: The monomer is phenylethene, C₆H₅CH=CH₂. Open the C=C bond and write the two carbon atoms with a single bond between them. The phenyl group remains on the second carbon. The repeat unit is [–CH₂–CH(C₆H₅)–]ₙ.
中文答案：单体是苯乙烯 C₆H₅CH=CH₂。打开 C=C 双键，写出两个碳原子并用单键连接。苯基保留在第二个碳原子上。重复单元为 [–CH₂–CH(C₆H₅)–]ₙ。
[–CH₂–CH(C₆H₅)–]ₙ
Examiners will credit the structure only if the double bond has been removed and the phenyl group is attached to the correct carbon. If you draw a C=C inside the repeat unit, the answer is wrong.
考官只有在双键被去除且苯基连接在正确碳原子上时才给分。如果在重复单元内画出 C=C，答案就是错误的。
10. Worked Example 2: Deducing a Monomer | 范例 2：反推单体
Question: A section of an addition polymer has the structure –CH₂–CH(CH₃)–CH₂–CH(CH₃)–CH₂–CH(CH₃)–. Deduce the structural formula and name of the monomer.
中文题目：某加成聚合物链段结构为 –CH₂–CH(CH₃)–CH₂–CH(CH₃)–CH₂–CH(CH₃)–。推断单体的结构式和名称。
Answer: The repeat unit is –CH₂–CH(CH₃)–. Remove the brackets and
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