📚 Addition Polymerisation | 加成聚合
Addition polymerisation is a key reaction type in organic chemistry where small unsaturated monomer molecules join together to form a long-chain polymer, without the loss of any small molecules. In the Edexcel IGCSE Science specification, you need to understand how monomers such as ethene and propene can become poly(ethene) and poly(propene), and how the structure of the polymer relates to its properties and uses.
加成聚合是有机化学中一类重要的反应，小分子的不饱和单体相互连接形成长链聚合物，且不会失去任何小分子。在 Edexcel IGCSE 科学大纲中，你需要理解乙烯和丙烯等单体如何转化为聚乙烯和聚丙烯，以及聚合物的结构如何影响其性质和用途。
1. Monomers and Polymers | 单体和聚合物
A monomer is a small, relatively simple molecule that can be joined together with many other identical or similar monomers to form a polymer. A polymer is a very large molecule (macromolecule) built up from repeating units derived from the original monomers.
单体是一种相对简单的小分子，可以与许多相同或相似的单体连接起来形成聚合物。聚合物是由原始单体衍生的重复单元构成的大分子（高分子）。
In addition polymerisation, the monomer must contain a carbon– e bond (C=C). The double bond opens up, allowing monomers to add to each other repeatedly.
在加成聚合中，单体必须含有碳碳双键（C=C）。双键打开，使单体能够反复相互加成。
2. Unsaturated Monomers | 不饱和单体
and propene (CH₃CH=CH₂). The double bond is the reactive site where polymerisation occurs.
加成聚合物由不饱和单体制成，即单体至少含有一个 C=C 双键。最常见的例子是烯烃，如乙烯（CH₂=CH₂）和丙烯（CH₃CH=CH₂）。双键是发生聚合反应的活性位点。
Because the double bond opens during polymerisation, the resulting polymer backbone is saturated, consisting only of single C–C bonds.
由于双键在聚合过程中打开，生成的聚合物主链是饱和的，仅由 C–C 单键构成。
3. The Polymerisation Reaction | 聚合反应过程
Addition polymerisation is an addition reaction. A large number of monomer molecules add together without the elimination of any small molecule such as water. The reaction typically requires high pressure, a catalyst, and sometimes elevated temperature.
加成聚合属于加成反应。大量单体分子相互加成，没有水等小分子脱去。该反应通常需要高压、催化剂，有时还需要高温。
The general equation for addition polymerisation of an alkene can be represented as:
n (monomer) → —[repeating unit]—ₙ
其中 n 表示聚合度，重复单元写在方括号内，下标 n 表示数量很大。
4. Formation of Poly(ethene) | 聚乙烯的生成
ene used to produce the addition polymer poly(ethene), commonly known as polythene. Under high pressure and with a suitable catalyst, the double bonds break and the carbon atoms form long saturated chains.
乙烯（CH₂=CH₂）是用于生产加成聚合物聚乙烯（俗称聚乙稀）的最简单烯烃。在高压和适当催化剂的作用下，双键断裂，碳原子形成长饱和链。
The reaction can be shown as:
n CH₂=CH₂ → —[CH₂–CH₂]—ₙ
The repeating unit is –CH₂–CH₂–, and the polymer contains no double bonds. This is why poly(ethene) is chemically inert.
重复单元是 –CH₂–CH₂–，聚合物中不含双键。因此聚乙烯化学性质稳定。
5. Formation of Poly(propene) | 聚丙烯的生成
tion polymerisation to produce poly(propene), a tough and flexible plastic. The methyl group (– tom along the chain influences the properties, making poly(propene) stronger and stiffer than poly(ethene).
丙烯（CH₃CH=CH₂）经加成聚合生成聚丙烯，这是一种坚韧且柔韧的塑料。链上每隔一个碳原子连接的甲基（–CH₃）会影响性质，使聚丙烯比聚乙烯更坚固、更硬挺。
Equation:
n CH₃CH=CH₂ → —[CH(CH₃)–CH₂]—ₙ
The repeating unit shows the side group. Polymers made from substituted alkenes often have commercially useful properties.
重复单元显示出侧基。由取代烯烃制成的聚合物通常具有商用价值。
6. Drawing Repeating Units | 画出重复单元
When drawing the repeating unit of an addition polymer, you must show the two carbon atoms that were originally in the double bond, now joined by a single bond, with the continuation bonds extending through the brackets. The subscript n is placed outside the brackets to indicate many repeats.
画加成聚合物的重复单元时，必须画出原来在双键中的两个碳原子，现在以单键连接，并用穿过括号的延伸键表示延续。下标 n 放在括号外，表示重复数量很多。
For poly(ethene): —[CH₂–CH₂]—ₙ. For poly(propene): —[CH(CH₃)–CH₂]—ₙ. In an exam, ensure the bond lines are clear and the groups are correctly positioned.
聚乙烯：—[CH₂–CH₂]—ₙ；聚丙烯：—[CH(CH₃)–CH₂]—ₙ。考试时，要确保键线清晰，基团位置正确。
7. Properties of Addition Polymers | 加成聚合物的性质
The physical properties of addition polymers depend on the structure of the monomer and the length of the polymer chain. Typically, addition polymers are low density solids, flexible, electrical insulators, and resistant to chemicals. They are thermosoftening (thermoplastics), meaning they soften when heated and can be remoulded.
加成聚合物的物理性质取决于单体的结构和聚合物链的长度。通常，加成聚合物是低密度固体、柔韧、电绝缘且耐化学腐蚀。它们是热塑性塑料，受热软化，可重新塑形。
| Polymer | Properties | Common Uses |
|---|---|---|
| Poly(ethene) | Flexible, lightweight, good chemical resistance | Plastic bags, bottles, cling film |
| Poly(propene) | Tough, higher softening temperature | Ropes, carpets, syringes |
| Poly(chloroethene) / PVC | Rigid when unplasticised, durable | Pipes, window frames, cable insulation |
| Poly(tetrafluoroethene) / PTFE | Non-stick, high heat resistance | Non-stick pans, plumber's tape |
These properties arise from the strong covalent bonds within the chains and weaker intermolecular forces between chains. Because the chains can slide past each other when heated, the materials can be recycled by melting and reshaping.
这些性质源于链内强共价键和链间较弱的分子间作用力。由于加热时链可以相互滑动，材料可通过熔化和重塑回收利用。
8. Difference between Addition and Condensation Polymerisation | 加成与缩聚的区别
In addition polymerisation, the polymer is the only product. In condensation polymerisation, two different monomers react and a small molecule, usually water or hydrogen chloride, is eliminated. For the IGCSE, you need to recognise that polyesters and polyamides are formed by condensation, while poly(ethene) and poly(propene) are addition polymers.
加成聚合中，聚合物是唯一的产物。缩聚反应中，两种不同单体反应，同时脱去小分子（通常是水或氯化氢）。在 IGCSE 阶段，需要识别聚酯和聚酰胺是缩合聚合物，而聚乙烯和聚丙烯是加成聚合物。
A simple memory trick: addition starts with alkene and adds monomers together; condensation often involves two functional groups and produces condensation water.
简单的记忆方法：加成从烯烃开始，把单体加在一起；缩合通常涉及两种官能团，生成水被缩去。
9. Environmental Considerations | 环境方面的考量
Addition polymers are versatile but create environmental problems. Most are non-biodegradable and persist in landfills or oceans for hundreds of years. Incineration of PVC, for example, can release toxic hydrogen chloride gas and dioxins if not carefully controlled.
加成聚合物用途广泛，但也带来环境问题。大多数聚合物不可生物降解，能在垃圾填埋场或海洋中存在数百年。例如，焚烧 PVC 若控制不当会释放有毒的氯化氢气体和二噁英。
Approaches to manage plastic waste include:
- Reducing the use of single-use plastics
- Reusing plastic items where possible
- Mechanical and chemical recycling to recover monomers or reform polymers
- Developing biodegradable polymers from renewable sources
管理塑料废物的方法包括：减少一次性塑料使用；尽可能重复使用塑料物品；机械和化学回收以回收单体或重塑聚合物；开发来自可再生资源的可生物降解聚合物。
10. Recycling and Feedstock Recycling | 回收与原料回收
Mechanical recycling involves sorting, washing, and melting waste plastics into new products. However, the quality can degrade after each cycle. Feedstock (or chemical) recycling breaks the polymer back down into monomers or small molecules that can be used to make new plastics or fuels.
机械回收包括分拣、清洗及将废塑料熔化制成新产品。但经过每个循环后质量会下降。原料（化学）回收将聚合物分解回单体或小分子，可用于制造新塑料或燃料。
An exam question may ask you to explain why recycling addition polymers is challenging: mixed polymer waste, contamination, and the need for clean separation all add to the difficulty.
考题可能会要求解释为何回收加成聚合物具有挑战性：混合塑料废物、污染以及需要清洁分离都增加了难度。
11. Common Misconceptions | 常见误解
has only single bonds. Another common error is forgetting to extend the continuation bonds through the brackets when drawing the polymer chain.
许多学生会混淆单体和重复单元。单体含有 C=C 双键，而重复单元只有单键。另一个常见错误是在画聚合物链时忘记将延伸键穿过括号。
Also, the polymer name should be placed in brackets when a simple prefix is used, e.g., poly(ethene) rather than polyethene in IUPAC-styled questions, though both are often accepted.
此外，使用简单前缀时聚合物名称应加括号，例如 poly(ethene) 而非 polyethene，在类似 IUPAC 命名的题目中，不过两者通常都可接受。
12. Summary and Revision Check | 总结与复习检查
Addition polymerisation converts alkenes into long-chain saturated polymers. The key points to remember are:
- Monomers have C=C double bonds
- No small molecules are lost
- Repeating unit is the smallest part of the polymer chain
- Properties determine uses; thermoplastics can be reshaped
- Plastic waste must be managed by reduce, reuse, recycle, and research into greener materials
加成聚合将烯烃转化为长链饱和聚合物。需记住的要点包括：单体有 C=C 双键；没有小分子失去；重复单元是聚合物链的最小部分；性质决定用途；热塑性塑料可重新塑形；必须通过减量、再利用、回收及研究绿色材料来管理塑料废物。
To test yourself, try drawing the repeating units for poly(butene) made from but-1-ene and for poly(phenylethene) (polystyrene). Explain why addition polymers have high melting points relative to small molecules but soften on heating.
自测一下：画出由 1-丁烯制成的聚丁烯和聚苯乙烯的重复单元。解释为什么加成聚合物相对于小分子有较高的熔点，但加热时会软化。
Published by TutorHao | Science Revision Series | aleveler.com
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