📚 Polymers | 聚合物
Welcome to this KS3 Chemistry revision guide on polymers. A polymer is a very large molecule made by joining together many small repeating units called monomers. In this article, you will learn how polymers form, how their structures affect their properties, and why they are so important in everyday life.
欢迎阅读本 KS3 化学"聚合物"复习指南。聚合物是由许多称为单体的小重复单元连接而成的非常大的分子。在本文中，你将学习聚合物如何形成、它们的结构如何影响性质，以及它们为何在日常生活中如此重要。
1. What Is a Polymer? | 什么是聚合物？
A polymer is a giant molecule made from thousands or millions of smaller molecules called monomers. The word 'polymer' comes from Greek: 'poly' means many and 'mer' means part, so a polymer is literally a many-part molecule.
聚合物是由成千上万个叫做单体的小分子组成的巨型分子。"聚合物"一词来自希腊语："poly"表示"许多"，"mer"表示"部分"，因此聚合物字面意思就是"多部分分子"。
Polymers are all around us. Plastics, rubber, wool, silk, paper, starch, proteins and DNA are all examples of polymers. Some are natural and some are synthetic, but they all share the same basic idea of a long chain made from repeating units.
聚合物在我们身边无处不在。塑料、橡胶、羊毛、丝绸、纸张、淀粉、蛋白质和 DNA 都是聚合物的例子。有些是天然的，有些是合成的，但它们都遵循同一种基本结构：由重复单元组成的长链。
Because polymer molecules are so large, chemists sometimes call them macromolecules. Their size and chain-like structure give them special physical properties that small molecules do not have.
由于聚合物分子非常大，化学家有时称它们为大分子。它们的尺寸和链状结构赋予了它们小分子所没有的特殊物理性质。
An important idea for KS3 is that a polymer is not just one big molecule - a sample of a plastic contains millions of these long chains packed together. The way the chains pack and interact with each other decides whether the material is soft and stretchy like a rubber band, or hard and rigid like a drinks bottle.
对 KS3 来说一个重要概念是：聚合物不只是一个大分子——一块塑料样品中其实包含数百万条这样的长链，它们紧密堆积在一起。这些链如何堆积、如何相互作用，决定了材料是像橡皮筋一样柔软有弹性，还是像饮料瓶一样坚硬刚强。
2. Monomers and Repeating Units | 单体与重复单元
Monomers are small, reactive molecules that can join together to make a polymer. The repeating unit is the smallest section of the polymer chain that is repeated again and again. For example, the monomer ethene forms the polymer poly(ethene).
单体是可以连接在一起形成聚合物的小分子。重复单元是聚合物链中一次又一次重复的最小部分。例如，乙烯单体会形成聚乙烯。
In poly(ethene), the repeating unit is -CH₂-CH₂-. This unit repeats many times to create a very long chain. The number of repeating units in a polymer chain is usually shown by the letter n, and n can be hundreds, thousands or even millions.
在聚乙烯中，重复单元是 -CH₂-CH₂-。这个单元重复很多次，形成一条非常长的链。聚合物链中重复单元的数目通常用字母 n 表示，n 可以是几百、几千甚至几百万。
The shorthand way of writing this is shown below. The brackets show which part repeats, and the n outside the bracket tells you it happens many times.
它的简写方式如下所示。方括号表示哪一部分在重复，括号外的 n 表示这种重复发生很多次。
n CH₂=CH₂ → -[CH₂-CH₂]ₙ-
Notice that the double bond between the two carbon atoms disappears when the polymer forms. Nothing is added and nothing is lost - the atoms of the monomer simply join together into a chain. This is a key idea that examiners look for.
注意，当聚合物形成时，两个碳原子之间的双键消失了。没有加入任何原子，也没有失去任何原子——单体的原子只是简单地连接成了一条链。这是考官非常看重的一个关键点。
3. Addition Polymerisation | 加聚反应
ether in one long chain. No other substance is produced - all the atoms of the monomers end up in the polymer.
加聚反应发生在许多含 C=C 双键的不饱和单体连接成一条长链时。反应不产生其他物质——单体的所有原子最终都进入了聚合物中。
The double bond opens up, and each carbon atom uses its spare bond to link to the next monomer. This repeats again and again, so a chain with thousands of carbon atoms is built very quickly.
双键打开，每个碳原子用一个多出来的键与下一个单体相连。这个过程不断重复，因此一条含数千个碳原子的链很快就建立起来了。
| Monomer 单体 | Polymer 聚合物 | Repeating unit 重复单元 |
| ethene 乙烯 | poly(ethene) 聚乙烯 | -CH₂-CH₂- |
| propene 丙烯 | poly(propene) 聚丙烯 | -CH₂-CH(CH₃)- |
| chloroethene 氯乙烯 | poly(chloroethene), PVC 聚氯乙烯 | -CH₂-CHCl- |
| tetrafluoroethene 四氟乙烯 | PTFE 聚四氟乙烯 | -CF₂-CF₂- |
ouble bond opening, and draw two bonds stretching out of the unit on either side. Add brackets around the unit and write n outside.
如果题目要求你画出重复单元，先找到 C=C 键，想象双键打开，然后在该单元两侧各画一根伸出的键。给单元加上方括号，并在括号外写上 n。
4. Condensation Polymerisation | 缩聚反应
In condensation polymerisation, two different monomers react together and a small molecule, such as water or hydrogen chloride, is lost each time a link is formed. This means the polymer does not contain all the atoms of the original monomers.
在缩聚反应中，两种不同的单体相互反应，每形成一个连接键就会失去一个小分子，例如水或氯化氢。这意味着聚合物并不包含原来单体的全部原子。
A typical example uses a diol (which has two -OH groups) and a dicarboxylic acid (which has two -COOH groups). When an -OH group meets a -COOH group, an ester link is made and a water molecule is released. The product is called a polyester.
一个典型的例子是用二醇（含有两个 -OH 基团）与二羧酸（含有两个 -COOH 基团）反应。当一个 -OH 基团遇到一个 -COOH 基团时，就形成酯键并释放一个水分子。产物称为聚酯。
If an amine group (-NH₂) reacts with a -COOH group instead, an amide link forms and water is lost again. Polymers made this way are called polyamides, and nylon is the best-known example.
如果改用氨基（-NH₂）与 -COOH 基团反应，则形成酰胺键，同样会失去水分子。这样制得的聚合物称为聚酰胺，尼龙就是最著名的例子。
| Feature 特征 | Addition 加聚 | Condensation 缩聚 |
| Number of monomers 单体种类 | usually one 通常一种 | usually two 通常两种 |
| C=C bond needed 需要 C=C | yes 是 | no 否 |
| Small molecule lost 失去小分子 | none 无 | water or HCl 水或氯化氢 |
5. Natural Polymers | 天然聚合物
Nature has been making polymers long before chemists did. Starch, cellulose, proteins, DNA and natural rubber are all natural polymers, and each one is built from its own kind of monomer.
早在化学家之前，大自然就一直在制造聚合物。淀粉、纤维素、蛋白质、DNA 和天然橡胶都是天然聚合物，每一种都由自己的单体构成。
Starch and cellulose are both made from glucose monomers joined together. Cellulose has straight chains that pack tightly, which is why it gives plant cell walls their strength. Starch has branched chains, which is why it is easier for your body to break down and use as an energy store.
淀粉和纤维素都由葡萄糖单体连接而成。纤维素的链是直的，能够紧密堆积，因此它赋予植物细胞壁强度。淀粉的链带有支链，因此更容易被人体分解并用作能量储存。
Proteins are polymers of amino acids linked by peptide (amide) bonds. The order of the amino acids decides the shape of the protein, and the shape decides its job - from carrying oxygen in blood to speeding up reactions as an enzyme.
蛋白质是由氨基酸通过肽键（酰胺键）连接而成的聚合物。氨基酸的排列顺序决定蛋白质的形状，而形状决定它的功能——从在血液中运输氧气，到作为酶加快反应速率。
DNA is a polymer of nucleotides. Its long double chain stores the genetic instructions that control how every living organism grows and works. Wool and silk, meanwhile, are natural protein fibres that humans have used for thousands of years.
DNA 是由核苷酸聚合而成的。它长长的双链储存着控制每个生物体生长和运作的遗传指令。而羊毛和丝绸则是人类使用了数千年的天然蛋白质纤维。
6. Synthetic Polymers and Plastics | 合成聚合物与塑料
Synthetic polymers are man-made. Most of them start from chemicals obtained by cracking crude oil, which is why plastics are closely linked to the petrochemical industry.
合成聚合物是人工制造的。它们大多以裂解原油得到的化学物质为原料，因此塑料与石油化工行业密切相关。
Common synthetic polymers include poly(ethene) for carrier bags and bottles, poly(propene) for ropes and food containers, PVC for window frames and pipes, polystyrene for packaging, and PET for drinks bottles and clothing fibres.
常见的合成聚合物包括：用于购物袋和瓶子的聚乙烯、用于绳索和食品容器的聚丙烯、用于窗框和管道的聚氯乙烯、用于包装的聚苯乙烯，以及用于饮料瓶和纺织纤维的 PET。
These materials are popular because they are cheap, light, strong, waterproof and easy to mould into almost any shape. They can also be coloured, made flexible or made rigid, which makes them incredibly useful.
这些材料之所以受欢迎，是因为它们便宜、轻便、坚固、防水，而且很容易塑造成几乎任何形状。它们还可以被染色，可以制成柔软的，也可以制成坚硬的，因此极其有用。
A useful KS3 habit is to link every plastic you meet to its monomer. If you know the monomer, you can work out the repeating unit, and that is exactly what exam questions often ask.
一个对 KS3 很有用的习惯是：把遇到的每一种塑料都与它的单体联系起来。只要知道单体，就能推算出重复单元，而这正是考题经常要求的内容。
7. Structure and Properties of Polymers | 聚合物的结构与性质
The properties of a polymer depend on three main features of its structure: the length of the chains, the amount of branching, and whether the chains are joined to each other by cross-links.
聚合物的性质主要取决于其结构的三个特征：链的长度、支链的多少，以及链与链之间是否通过交联相连。
Longer chains have stronger forces between them, so they need more energy to separate. This makes the polymer stronger and gives it a higher melting point than a similar polymer with short chains.
链越长，链与链之间的作用力越强，因此需要更多能量才能使它们分开。这使聚合物更坚固，熔点也比链较短的同类聚合物更高。
Branched chains cannot pack together as neatly as straight chains. The gaps between them make the material softer, less dense and more flexible, because the chains can slide past each other more easily.
带支链的链不能像直链那样整齐地堆积。链之间的空隙使材料更柔软、密度更低、更柔韧，因为链更容易彼此滑动。
| Structural feature 结构特征 | Effect on properties 对性质的影响 |
| very long chains 很长的主链 | stronger, higher melting point 更强、熔点更高 |
| branched chains 支链 | softer, more flexible 更软、更柔韧 |
| cross-links 交联 | rigid, cannot be remelted 刚硬、无法重新熔融 |
8. Thermoplastics and Thermosetting Plastics | 热塑性与热固性塑料
A thermoplastic is a polymer whose chains are held together only by weak intermolecular forces. When it is heated, these forces break and the chains slide over each other, so the plastic softens and can be reshaped.
热塑性塑料是一种链与链之间仅靠微弱分子间作用力结合的聚合物。加热时，这些作用力被破坏，链可以相互滑动，因此塑料变软并可以重新塑形。
A thermosetting plastic has covalent cross-links between its chains. These strong bonds stop the chains from sliding, so the material cannot be softened or remoulded. Heating it strongly simply causes it to char or decompose.
热固性塑料的链与链之间存在共价交联。这些强键阻止了链的滑动，因此材料无法软化或重新塑形。强烈加热只会使它烧焦或分解。
| Property 性质 | Thermoplastic 热塑性 | Thermosetting 热固性 |
| Bonds between chains 链间作用 | weak forces 微弱作用力 | covalent cross-links 共价交联 |
| On heating 加热时 | softens, can be remoulded 变软、可重塑 | does not soften 不变软 |
| Examples 例子 | poly(ethene), PET 聚乙烯、PET | bakelite, melamine 电木、三聚氰胺 |
9. Forces Between Polymer Chains | 聚合物链之间的作用力
It is important not to confuse the covalent bonds inside a polymer chain with the forces between different chains. The bonds inside the chain are strong covalent bonds, while the forces between chains are much weaker.
重要的是不要把聚合物链内部的共价键与不同链之间的作用力混淆。链内部的键是强共价键，而链与链之间的作用力要弱得多。
When a thermoplastic is heated, it is the weak forces between the chains that break, not the covalent bonds. That is why the plastic becomes soft and flexible but does not fall apart into small molecules.
加热热塑性塑料时，被破坏的是链之间的微弱作用力，而不是共价键。这就是为什么塑料会变软变柔韧，却不会分解成小分子。
This also explains why plastics do not dissolve easily and do not boil at low temperatures. To break a polymer completely you would need enough energy to break thousands of strong covalent bonds, which requires a very high temperature.
这也解释了为什么塑料不易溶解，也不会在低温下沸腾。要彻底破坏一个聚合物，你需要足够的能量去打断成千上万个强共价键，这需要非常高的温度。
10. Polymers in Everyday Life | 日常生活中的聚合物
Think about the objects you used this morning: your toothbrush handle, your water bottle, your school bag, your trainers, your phone case, the fibres in your uniform. Almost all of them contain polymers.
想一想你今天早上用过的物品：牙刷柄、水瓶、书包、运动鞋、手机壳、校服纤维。它们几乎都含有聚合物。
- Packaging: poly(ethene) bags, polystyrene trays, bubble wrap 包装：聚乙烯袋、聚苯乙烯托盘、气泡膜
- Clothing: polyester, nylon, acrylic fibres, plus natural wool and silk 衣物：聚酯、尼龙、腈纶纤维，以及天然羊毛和丝绸
- Building: PVC pipes, window frames, insulation foam, paints 建筑：PVC 管道、窗框、保温泡沫、涂料
- Medicine: disposable syringes, gloves, blood bags, dissolvable stitches 医疗：一次性注射器、手套、血袋、可吸收缝合线
- Transport: tyres, seat covers, dashboards, safety belts 交通：轮胎、座椅面料、仪表盘、安全带
Because polymers are so cheap and versatile, global production has risen enormously since the 1950s. The same properties that make them useful - being strong and unreactive - also make them difficult to get rid of.
由于聚合物廉价且用途广泛，自 20 世纪 50 年代以来全球产量大幅增长。让它们有用的那些性质——坚固且不易反应——同时也使它们难以被处理掉。
11. Environmental Issues and Recycling | 环境问题与回收
Most synthetic polymers are not biodegradable, meaning bacteria and fungi cannot break them down. A plastic bottle may take hundreds of years to fragment, and it never truly disappears.
大多数合成聚合物不可生物降解，也就是说细菌和真菌无法将它们分解。一个塑料瓶可能需要数百年才能碎裂，而且它永远不会真正消失。
Plastic waste in the oceans breaks into tiny pieces called microplastics. These are eaten by fish and other animals, and they can enter the food chain. Burning plastics can also release toxic gases unless it is done in a controlled way.
海洋中的塑料垃圾会碎裂成称为微塑料的小颗粒。它们被鱼类和其他动物吃下，并可能进入食物链。塑料燃烧还可能释放有毒气体，除非在受控条件下进行。
- Reduce: use fewer single-use items 减少：少用一次性物品
- Reuse: refill bottles and bags 重复使用：重复灌装瓶子和袋子
- Recycle: sort plastics by type so they can be melted and remoulded 回收：按种类分拣塑料，使其可被熔化重塑
- Replace: use biodegradable polymers made from plants, such as PLA 替换：使用由植物制成的可生物降解聚合物，如 PLA
Thermoplastics are much easier to recycle than thermosetting plastics, because they can be melted down and reshaped. This is one reason why sorting plastic waste properly matters so much.
热塑性塑料比热固性塑料更容易回收，因为它们可以熔化并重新塑形。这也是正确分类塑料垃圾如此重要的原因之一。
12. Exam Tips and Key Vocabulary | 考试要点与核心词汇
Polymer questions reward precise language. Always use the words monomer, repeating unit, chain and intermolecular force, and make sure you can explain the difference between addition and condensation polymerisation in one sentence each.
聚合物题目奖励精确的表达。始终使用单体、重复单元、链和分子间作用力这些词，并确保你能各用一句话解释加聚反应和缩聚反应的区别。
- When drawing a repeating unit, use brackets with n outside and two bonds crossing the brackets. 画重复单元时，用带 n 的方括号，并画出两根穿过括号的键。
- Never add or remove atoms in addition polymerisation - just open the C=C bond. 加聚反应中不要添加或去掉原子——只需打开 C=C 键。
- In condensation polymerisation, always state which small molecule is lost. 缩聚反应中，一定要写明失去了哪种小分子。
- Link properties to structure: long chains, branching and cross-links. 把性质与结构联系起来：长链、支链和交联。
| Term 术语 | Meaning 含义 |
| monomer 单体 | small molecule that joins to form a polymer 连接形成聚合物的小分子 |
| repeating unit 重复单元 | the part of the chain that repeats 链中重复的部分 |
| macromolecule 大分子 | a very large molecule 非常大的分子 |
| cross-link 交联 | a bond joining two polymer chains 连接两条聚合物链的键 |
| biodegradable 可生物降解的 | broken down by living organisms 能被生物分解 |
Revise polymers by linking each material to its monomer and repeating unit, then practise explaining properties using structure. That combination covers almost every
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