📚 GCSE Chemistry: Polymers Key Points | GCSE 化学：聚合物 考点精讲
Polymers are all around us, from the plastic bottle you drink from to the DNA inside your cells. In GCSE Chemistry, understanding polymers means diving into how small molecules join together to form giant chains, the difference between addition and condensation polymerisation, and why this matters for both everyday materials and the environment. This revision guide will walk you through every key point you need to know, with clear explanations and paired English-Chinese notes.
聚合物无处不在，从你喝水的塑料瓶到细胞内的 DNA。在 GCSE 化学中，理解聚合物意味着深入探究小分子如何连接成巨大长链，加成聚合与缩合聚合的区别，以及这对日常材料和环境的重要性。这篇复习指南将带你梳理所有你需要掌握的要点，并提供清晰的中英双语讲解。
1. What are Polymers? | 什么是聚合物？
A polymer is a substance made of very large molecules. These giant molecules are formed when many small, repeating units called “monomers” join together through chemical bonds. The word “polymer” comes from Greek: “poly” meaning many and “mer” meaning parts. Polymers can be natural, like proteins and cellulose, or synthetic, like plastics and nylon. The length of the polymer chain can contain hundreds or thousands of monomer units, which gives polymers their unique properties such as flexibility, strength, and the ability to be moulded into shapes.
聚合物是由非常大的分子构成的物质。这些巨型分子是由许多称为 “单体” 的小重复单元通过化学键连接在一起形成的。”聚合物” 一词源于希腊语：”poly” 意为多，”mer” 意为部分。聚合物可以是天然的，如蛋白质和纤维素，也可以是合成的，如塑料和尼龙。聚合物链的长度可以包含数百或数千个单体单元，这赋予了聚合物独特的性质，如柔韧性、强度以及可塑造成各种形状的能力。
2. Monomers and Polymerisation | 单体和聚合反应
Monomers are small, reactive molecules that can bond with each other to form a polymer. The process of linking monomers together is called polymerisation. There are two main types of polymerisation you need to know for GCSE: addition polymerisation and condensation polymerisation. The key difference is that addition polymerisation involves monomers with a carbon-carbon double bond (C=C) and no other products are formed, while condensation polymerisation involves two different functional groups and a small molecule, often water, is eliminated each time a bond forms.
单体是能够相互键合形成聚合物的小型活性分子。将单体连接起来的过程称为聚合反应。GCSE 需要掌握两种主要的聚合反应类型：加成聚合和缩合聚合。关键区别在于，加成聚合涉及含有碳碳双键 (C=C) 的单体，且不产生其他产物；而缩合聚合涉及两种不同的官能团，每次形成新键时都会脱去一个小分子，通常是水。
3. Addition Polymerisation | 加成聚合
Addition polymerisation only occurs with monomers that contain a carbon-carbon double bond, such as ethene (CH₂=CH₂), propene, and styrene. During the reaction, the double bond opens up, and the monomers add to each other to form a long saturated chain. There are no by-products; all atoms from the monomer end up in the polymer. The general equation for addition polymerisation can be represented as:
加成聚合只发生在含有碳碳双键的单体上，例如乙烯 (CH₂=CH₂)、丙烯和苯乙烯。反应过程中，双键打开，单体相互加成形成长长的饱和碳链。没有副产物产生；单体中的所有原子都进入聚合物中。加成聚合的通式可表示为：
n CH₂=CH₂ → [-CH₂-CH₂-]ₙ
Here, n represents a very large number of repeating units. The repeating unit inside the brackets is called the polymer repeat unit, and its structure depends on the original monomer. The name of the polymer is formed by putting “poly” in front of the monomer name, often in brackets if the monomer name has more than one word (e.g., poly(ethene), poly(propene)).
这里，n 代表数量极大的重复单元。方括号内的重复单元称为聚合物的重复单元，其结构取决于原始单体。聚合物的名称是在单体名称前加上 “poly”，如果单体名称多于一个词，则通常加上括号（例如 poly(ethene)，聚丙烯）。
To draw the repeat unit from a monomer, simply break the C=C double bond and extend single bonds to either side. For example, from propene (CH₂=CHCH₃), the repeat unit becomes -CH₂-CH(CH₃)-. It is essential to show the continuation of the chain with bonds extending through the brackets.
由单体绘制重复单元时，只需断开 C=C 双键并向两侧延伸单键。例如，由丙烯 (CH₂=CHCH₃) 得到的重复单元为 -CH₂-CH(CH₃)-。必须用穿越括号的键来表示链的延续。
4. Common Addition Polymers | 常见加成聚合物
The properties and uses of addition polymers depend on the monomer and the conditions of polymerisation. Below is a table of key addition polymers you should be familiar with for your GCSE exam:
加成聚合物的性质和用途取决于单体及聚合条件。以下是 GCSE 考试中需要熟悉的关键加成聚合物表：
| Polymer | 聚合物 | Monomer | 单体 | Properties | 性质 | Uses | 用途 |
|---|---|---|---|
| Poly(ethene) / PE | 聚乙烯 | Ethene | 乙烯 | Flexible, cheap, good insulator (LDPE); stronger, more rigid (HDPE) | Plastic bags, bottles, pipes |
| Poly(propene) / PP | 聚丙烯 | Propene | 丙烯 | Tough, flexible, resistant to heat | Food containers, ropes, carpets |
| Poly(chloroethene) / PVC | 聚氯乙烯 | Chloroethene | 氯乙烯 | Stiff (unplasticised), flexible (plasticised), durable | Window frames, pipes, cable insulation |
| Poly(styrene) / PS | 聚苯乙烯 | Styrene | 苯乙烯 | Brittle as solid; can be expanded into lightweight foam | Packaging, insulation, disposable cups |
Note that poly(ethene) can be low-density (LDPE) or high-density (HDPE) depending on the pressure and catalyst used during polymerisation. LDPE has branched chains, making it more flexible, while HDPE has straight chains, making it stronger.
注意，聚乙烯可根据聚合时的压力和催化剂分为低密度（LDPE）和高密度（HDPE）。LDPE 具有支链结构，因而更柔韧；HDPE 具有直链结构，因而强度更高。
5. Condensation Polymerisation | 缩合聚合
Condensation polymerisation usually involves two different types of monomer, each with at least two functional groups. When these functional groups react together, a bond is formed and a small molecule – most commonly water – is eliminated. This is why it is called “condensation”. The simplest examples are polyesters (formed from a diol and a dicarboxylic acid) and polyamides (formed from a diamine and a dicarboxylic acid). Unlike addition polymers, condensation polymers have atoms from both monomers in their backbone, and the repeat unit contains ester or amide links.
缩合聚合通常涉及两种不同类型的单体，每种单体至少带有两个官能团。当这些官能团彼此反应时，会形成新键并脱去一个小分子——最常见的是水。这就是为什么它被称为 “缩合”。最简单的例子是聚酯（由二醇和二羧酸形成）和聚酰胺（由二胺和二羧酸形成）。与加成聚合物不同，缩合聚合物的主链包含来自两种单体的原子，且重复单元中含有酯键或酰胺键。
To write the equation for a condensation polymerisation, you need to identify the functional groups and show the repeat unit with the new link. A typical polyester formation is:
要写出缩合聚合的方程式，你需要识别官能团并展示带有新键的重复单元。一个典型的聚酯形成反应为：
n HOOC-C₆H₄-COOH + n HO-CH₂CH₂-OH → [-OC-C₆H₄-COO-CH₂CH₂-O-]ₙ + (2n-1) H₂O
Often, the equation is simplified to show n repeating units losing n water molecules in total, but you must remember that each ester link formed releases one water molecule. The repeat unit always shows the linkage between the monomers.
该方程式通常会简化为 n 个重复单元共脱去 n 个水分子，但必须记住，每形成一个酯键释放一个水分子。重复单元始终要展示单体之间的连接键。
6. Polyesters and Polyamides | 聚酯和聚酰胺
Polyesters are condensation polymers formed from a dicarboxylic acid and a diol. The ester link (-COO-) is the functional group that connects the monomers. A famous example is polyethylene terephthalate (PET), used for drinks bottles and clothing fibres. The monomers are terephthalic acid (benzene-1,4-dicarboxylic acid) and ethane-1,2-diol.
聚酯是由二羧酸和二醇形成的缩合聚合物。酯键 (-COO-) 是连接单体的官能团。一个著名的例子是聚对苯二甲酸乙二酯 (PET)，用于饮料瓶和服装纤维。其单体是对苯二甲酸（苯-1,4-二甲酸）和乙二醇。
Polyamides are formed from a dicarboxylic acid and a diamine. The amide link (-CONH-) holds the chain together. Nylon is a common polyamide, often made from hexanedioic acid and 1,6-diaminohexane. Both polyesters and polyamides contain polar groups that can form hydrogen bonds, giving them high strength and melting points.
聚酰胺由二羧酸和二胺形成。酰胺键 (-CONH-) 将链连接在一起。尼龙是一种常见的聚酰胺，通常由己二酸和 1,6-己二胺制成。聚酯和聚酰胺都含有可形成氢键的极性基团，因此它们具有高强度和高熔点。
7. Thermoplastics vs Thermosets | 热塑性塑料与热固性塑料
Polymers can be classified by their behaviour when heated. Thermoplastics soften when heated and harden when cooled, a process that can be repeated many times. This is because the polymer chains are held together by weak intermolecular forces that weaken on heating, allowing the chains to slide past each other. Examples include poly(ethene), poly(propene) and PVC. They are ideal for recycling because they can be reshaped.
聚合物可按加热时的行为分类。热塑性塑料加热时软化，冷却时变硬，这一过程可重复多次。这是因为聚合物链之间由较弱的分子间作用力连接，加热时作用力减弱，链可以相互滑过。例子包括聚乙烯、聚丙烯和 PVC。它们适合回收利用，因为可以重新塑形。
Thermosetting polymers, or thermosets, do not soften when heated. Instead, they char or burn because they have strong covalent cross-links between chains. Once the polymer has set into its initial shape, it cannot be remoulded. These cross-links form during the curing process. Thermosets are used when heat resistance is needed, such as in electrical plugs, saucepan handles, and some adhesives. Melamine is a typical example.
热固性聚合物在加热时不会软化，而是会烧焦或燃烧，因为它们分子链之间有牢固的共价交联。一旦聚合物定型为初始形状，就无法再次重塑。这些交联是在固化过程中形成的。热固性塑料用于需要耐热的场合，如电插头、锅柄和某些粘合剂。三聚氰胺是一个典型例子。
8. Properties and Uses of Polymers | 聚合物的性质与用途
The properties of a polymer are determined by several factors: the length of the polymer chain, the presence of branches or cross-links, the type of intermolecular forces, and the flexibility of the chains. Longer chains have stronger intermolecular forces, making the material tougher. Branching reduces the packing efficiency, lowering density and melting point. Cross-links make the polymer rigid and thermosetting.
聚合物的性质由多个因素决定：聚合物链的长度、支链或交联的存在、分子间作用力的类型以及链的柔韧性。更长的链有更强的分子间作用力，使材料更坚韧。支化会降低堆积效率，从而降低密度和熔点。交联使聚合物变得刚硬并成为热固性材料。
For GCSE, you need to link specific properties to uses. For example, poly(ethene) is a good electrical insulator and is flexible, so it is used for coating electric wires. PVC is stiff when unplasticised, making it suitable for window frames, but can be made flexible by adding plasticisers, which allows it to be used for clothing or hoses. Polymer foams, like expanded polystyrene, are excellent thermal insulators because they trap air.
在 GCSE 中，你需要将特定性质与用途联系起来。例如，聚乙烯是良好的电绝缘体且柔韧，因而用于电线包覆。未增塑的 PVC 硬挺，适合制作窗框，但加入增塑剂后可变得柔软，用于服装或软管。泡沫聚合物，如发泡聚苯乙烯，因能截留空气而成为优良的隔热材料。
9. Environmental Impact of Polymers | 聚合物的环境影响
Most synthetic polymers are non-biodegradable, meaning they are not broken down by microorganisms. This leads to serious environmental problems when they are discarded as waste. Landfill takes up space and can cause pollution; incineration can generate toxic gases if not controlled properly. Plastics in the ocean break down into microplastics, which enter the food chain and harm wildlife.
大多数合成聚合物是不可生物降解的，这意味着它们不会被微生物分解。当它们被作为废弃物丢弃时，会导致严重的环境问题。填埋会占用空间并可能造成污染；焚烧如果控制不当会产生有毒气体。海洋中的塑料会分解成微塑料，进入食物链并危害野生动物。
To reduce the impact, we can recycle polymers. However, different types of polymers must be sorted carefully because they have different properties. Recycling can be mechanical (melting and remoulding) or chemical (breaking down into monomers). Biodegradable polymers are also being developed from renewable sources, such as corn starch. Additionally, we can reduce our use of single-use plastics and reuse items where possible.
为减少影响，我们可以回收聚合物。但不同类型的聚合物必须仔细分类，因为它们性质不同。回收可是机械的（熔化并重塑）或化学的（分解为单体）。人们还在开发来自可再生资源（如玉米淀粉）的可生物降解聚合物。此外，我们可以减少一次性塑料的使用，并尽可能地重复使用物品。
10. Biopolymers and Sustainability | 生物聚合物与可持续性
Biopolymers are polymers produced from biomass, such as plants. Polylactic acid (PLA) is made from corn starch or sugar cane. It is biodegradable under industrial composting conditions and is used for packaging, disposable cups, and medical stitches. Unlike conventional plastics derived from crude oil, biopolymers can be renewable and have a lower carbon footprint. However, growing crops for bioplastics requires land and water, which raises concerns about competing with food resources.
生物聚合物是由生物质（如植物）生产的聚合物。聚乳酸 (PLA) 由玉米淀粉或甘蔗制成，在工业堆肥条件下可生物降解，用于包装、一次性杯子和医用缝合线。与源自原油的传统塑料不同，生物聚合物可再生且碳足迹较低。然而，种植生物塑料原料需要土地和水资源，引发了与粮食资源竞争的担忧。
Another example is cellulose-based polymers, where the natural polymer cellulose is chemically modified to improve its properties. These materials still face challenges in terms of cost and durability. GCSE questions may ask you to evaluate the advantages and disadvantages of biopolymers versus traditional polymers, so you should be able to discuss both the environmental benefits and the practical limitations.
另一个例子是纤维素基聚合物，即对天然聚合物纤维素进行化学改性以增强其性能。这些材料在成本和耐久性方面仍面临挑战。GCSE 题目可能会要求你评价生物聚合物与传统聚合物的优缺点，因此你应能够讨论环境效益和实际局限性两个方面。
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