IGCSE Chemistry: Polymers – Key Concepts and Exam Tips | IGCSE 化学：聚合物 考点精讲

📚 IGCSE Chemistry: Polymers – Key Concepts and Exam Tips | IGCSE 化学：聚合物 考点精讲

Polymers are giant molecules made by linking together many small repeating units called monomers. In IGCSE Chemistry, you need to understand how addition and condensation polymerisation work, be able to draw repeat units from given monomers, and recognise the uses and environmental impact of common plastics. This article consolidates all the key ideas, gives clear explanations, and highlights typical exam traps.

聚合物是由许多称为单体的小重复单元连接而成的巨型分子。在IGCSE化学中，你需要理解加成聚合和缩合聚合的原理，能够根据给定单体画出重复单元，并认识常见塑料的用途和环境影响。本文梳理所有核心概念，提供清晰讲解，并点出考试中常见的易错点。

1. Introduction to Polymers | 聚合物简介

A polymer is a long-chain molecule formed when many small molecules, known as monomers, join together. The process of forming a polymer is called polymerisation. Polymers can be synthetic, such as plastics and nylon, or natural, such as starch, proteins and DNA. The properties of a polymer depend on the monomer used and the type of linkage between them.

聚合物是由许多称为单体的小分子连接而成的长链分子。形成聚合物的过程称为聚合反应。聚合物可以是合成的，例如塑料和尼龙，也可以是天然的，例如淀粉、蛋白质和DNA。聚合物的性质取决于所用的单体以及它们之间的连接方式。

In IGCSE, the two main types of polymerisation are addition polymerisation and condensation polymerisation. Addition polymers are made from alkenes, where the double bond opens up to form a single-bonded chain. Condensation polymers form when monomers join with the elimination of a small molecule, usually water.

在IGCSE中，两种主要的聚合类型是加成聚合和缩合聚合。加成聚合物由烯烃制成，其中双键打开形成单键链。缩合聚合则是单体连接并消去一个小分子，通常是水，从而形成聚合物。

2. Monomers, Polymers and Repeat Units | 单体、聚合物和重复单元

A monomer is a small molecule that acts as a building block for a polymer. The repeat unit is the smallest group of atoms that, when repeated many times, gives the structure of the polymer chain. For an addition polymer, the repeat unit has the same atoms as the monomer but with a single bond instead of the double bond.

单体是作为聚合物构件的小分子。重复单元是重复无数次后构成聚合物链结构的最小原子基团。对于加成聚合物，重复单元的原子组成与单体相同，但以单键代替双键。

example, the monomer ethene (CH₂=CH₂) forms the polymer poly(ethene) with the repeat unit —(CH₂—CH₂)—. The 'n' structure of a polymer from its monomer and identify the monomer from a given repeat unit.

例如，单体乙烯（CH₂=CH₂）形成聚合物聚乙烯，其重复单元为—(CH₂—CH₂)—。括号外的n表示该单元重复n次。你必须能够从单体画出聚合物结构，并能从给定的重复单元识别出单体。

In poly(propene), the monomer is CH₂=CHCH₃. The repeat unit is —(CH₂—CH(CH₃))—, where a methyl group is attached to every other carbon in the chain.

在聚丙烯中，单体是CH₂=CHCH₃。重复单元为—(CH₂—CH(CH₃))—，其中每隔一个碳原子上连有一个甲基。

3. Addition Polymerisation Mechanism | 加成聚合反应机理

nder high pressure and with a catalyst, the double bonds break, and the units link to form a saturated carbon chain. No other product is formed; all atoms from the monomer become part of the polymer.

加成聚合发生在含有碳碳双键（C=C）的不饱和单体上。在高压和催化剂作用下，双键断裂，单体单元连接形成饱和碳链。不生成其他产物；单体中的所有原子都成为聚合物的一部分。

The general equation for addition polymerisation can be written as: n A=A → —(A—A)ₙ— acromolecular change, and you may be asked to write an equation using structural formulae.

加成聚合的一般方程式可写作：n A=A → —(A—A)ₙ—，其中A代表单体的其余部分。该反应是形成大分子的重要示例，考试中可能要求用结构式书写方程式。

The polymerisation of ethene: n CH₂=CH₂ → —(CH₂—CH₂)ₙ— dicate continuation. In exam answers, you can show the repeat unit in square brackets with 'n' as a subscript outside.

乙烯的聚合：n CH₂=CH₂ → —(CH₂—CH₂)ₙ—。聚合物链通常两端用开口键表示延伸。在答题时可使用方括号将重复单元括起，并在括号外以下标n表示。

4. Drawing and Interpreting Repeat Units | 绘制与解读重复单元

When drawing a repeat unit from an alkene monomer, replace the C=C double bond with a C— bonds extending out of the brackets. Always check that the number of hydrogen atoms matches the original monomer.

在由烯烃单体绘制重复单元时，将C=C双键替换为C—C单键，并画出连在碳原子上的基团。横向拉伸结构，用括号括起，并让延伸键伸出括号外。务必核对氢原子数目是否与原单体一致。

For example, poly(chloroethene) (PVC) from chloroethene CH₂=CHCl: the repeat unit is —(CH₂—CHCl)— e swapping between monomer and repeat unit until you can do it quickly in both directions.

例如，聚氯乙烯（PVC）由氯乙烯CH₂=CHCl得到：重复单元为—(CH₂—CHCl)—。常见错误包括漏画延伸键，或将取代基放在错误的碳上。反复练习单体与重复单元之间的相互转换，直到能快速完成两个方向的书写。

5. Common Addition Polymers: Poly(ethene) and Poly(propene) | 常见加成聚合物：聚乙烯和聚丙烯

Poly(ethene), commonly known as polythene, is the most widely used plastic. It is lightweight, flexible and a good electrical insulator, making it suitable for plastic bags, bottles and cling film. It is formed by the addition polymerisation of ethene under high pressure and temperature with a Ziegler-Natta catalyst.

聚乙烯（俗称塑料薄膜）是应用最广泛的塑料。它质轻、柔韧且是良好的电绝缘体，适用于塑料袋、瓶子和保鲜膜。它是在高压、高温及齐格勒-纳塔催化剂下由乙烯加成聚合而成。

Poly(propene) is a stronger and stiffer polymer used to make ropes, crates and car bumpers. The presence of the CH₃ group on the chain makes the polymer more rigid. Both polymers are saturated hydrocarbons and are unreactive, contributing to their durability – but also to their persistence in landfill.

聚丙烯是一种更强、更硬的聚合物，用于制造绳索、板条箱和汽车保险杠。链上CH₃基团的存在使聚合物更刚硬。这两种聚合物都是饱和烃，化学性质稳定，这正是它们经久耐用的原因——但也导致它们在填埋场中长期存在。

6. Other Important Addition Polymers: PVC, Polystyrene and PTFE | 其他重要加成聚合物：聚氯乙烯、聚苯乙烯和聚四氟乙烯

Poly(chloroethene), better known as PVC, is made from chloroethene. The chlorine atom makes the polymer harder and flame-resistant. PVC is used for drainpipes, window frames and insulation on electrical wires. Unplasticised PVC (uPVC) is rigid, while plasticised PVC is flexible.

聚氯乙烯（PVC）由氯乙烯制成。氯原子使聚合物更硬且阻燃。PVC用于排水管、窗框和电线绝缘层。未增塑的PVC（uPVC）是刚性的，而增塑后的PVC则柔韧。

t is a clear, brittle solid used in disposable cups, packaging and insulation as expanded polystyrene foam. The bulky phenyl side group prevents close packing of chains, making it light and good for thermal insulation.

聚苯乙烯由苯乙烯（C₆H₅CH=CH₂）制成。它是一种透明、脆性的固体，用于一次性杯子、包装，发泡聚苯乙烯泡沫则用于保温。庞大的苯基侧基阻碍了链的紧密堆积，使其质轻并具有优良的隔热性能。

. It has a very low coefficient of friction and is highly heat-resistant, so it is used as a non-stick coating on pans and in electrical insulation. Its repeat unit is —(CF₂—CF₂)ₙ—.

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聚四氟乙烯（PTFE）由四氟乙烯CF₂=CF₂制成。它具有极低的摩擦系数和优异的耐热性，因此用作锅具的不粘涂层和电绝缘材料。其重复单元为—(CF₂—CF₂)ₙ—。

7. Thermoplastics vs. Thermosets | 热塑性塑料与热固性塑料

Thermoplastics soften when heated and harden when cooled, and this cycle can be repeated many times. They consist of linear or branched polymer chains with no cross-links, allowing the chains to slide past each other when softened. Poly(ethene), PVC and polystyrene are common thermoplastics.

热塑性塑料受热时软化，冷却时硬化，这一循环可反复多次。它们由直链或支链聚合物构成，没有交联，软化时链可以相互滑动。聚乙烯、PVC和聚苯乙烯是常见的热塑性塑料。

Thermosets, on the other hand, do not soften when reheated because they have strong covalent cross-links between polymer chains. These cross-links give a rigid, three-dimensional network. Once set, thermosets cannot be remoulded. Examples include bakelite and melamine, used in electrical plugs and kitchen surfaces.

热固性塑料则不同，再次加热时不会软化，因为聚合物链之间具有强共价交联。这些交联形成了刚性的三维网络。一旦固化，热固性塑料就无法重新塑形。例子包括电木和美耐皿，用于电插头和厨房台面。

Examiners often ask you to explain these differences in terms of structure. Link the absence or presence of cross-links to the ability of chains to move when heated.

考官常要求从结构角度解释这些差异。要将交联的存在与否与加热时链段的运动能力联系起来进行说明。

8. Condensation Polymers: Polyesters and Polyamides (Nylon) | 缩合聚合物：聚酯和聚酰胺（尼龙）

Condensation polymerisation involves monomers with two functional groups per molecule. When these monomers react, a small molecule, usually water or hydrogen chloride, is eliminated. The two main types on the IGCSE syllabus are polyesters and polyamides (nylon).

缩合聚合涉及每个分子带有两个官能团的单体。这些单体反应时，会脱去一个小分子，通常是水或氯化氢。IGCSE大纲中主要的两类是聚酯和聚酰胺（尼龙）。

A polyester is formed from a dicarboxylic acid and a diol. Each —COOH group reacts with an —OH group to form an ester linkage —COO—, with the elimination of water. The most common example is poly(ethylene terephthalate), PET, used for drinks bottles and clothing fibres.

聚酯由二元羧酸和二元醇形成。每个—COOH基团与一个—OH基团反应，生成酯键—COO—，同时脱去水。最常见的例子是聚对苯二甲酸乙二醇酯（PET），用于饮料瓶和服装纤维。

A polyamide such as nylon is made from a dicarboxylic acid and a diamine. The —COOH group reacts with the —NH₂ group to form an amide linkage —CONH—, again with the loss of water. Nylon is used in ropes, stockings and parachutes because of its strength and elasticity.

聚酰胺如尼龙是由二元羧酸和二元胺制成的。—COOH基团与—NH₂基团反应形成酰胺键—CONH—，同样脱去水。尼龙因其强度和弹性而用于绳索、丝袜和降落伞。

You do not need to draw the full mechanism, but you must be able to identify the repeat unit from given monomer structures and write a simplified equation showing the elimination of small molecules.

无需画出完整的反应机理，但必须能够根据给定的单体结构识别重复单元，并写出显示小分子脱去的简化方程式。

9. Natural Polymers: Starch, Proteins and DNA | 天然聚合物：淀粉、蛋白质和DNA

Natural polymers are produced by living organisms. Starch and cellulose are condensation polymers made from glucose monomers. Starch is a mixture of amylose and amylopectin, both formed by glycosidic linkages between α-glucose molecules. It serves as an energy store in plants.

天然聚合物由生物体产生。淀粉和纤维素是由葡萄糖单体缩合而成的聚合物。淀粉是直链淀粉和支链淀粉的混合物，两者均由α-葡萄糖分子间的糖苷键形成。它在植物中储存能量。

Proteins are condensation polymers made from amino acid monomers. Amino acids contain an amine group (—NH₂) and a carboxylic acid group (—COOH). They join by peptide bonds (—CONH—) with elimination of water. The order of amino acids determines the protein's shape and function.

蛋白质是由氨基酸单体缩合而成的聚合物。氨基酸含有氨基（—NH₂）和羧酸基团（—COOH）。它们通过肽键（—CONH—）连接，同时脱去水。氨基酸的顺序决定了蛋白质的形状和功能。

DNA (deoxyribonucleic acid) is also a condensation polymer formed from nucleotide monomers. Each nucleotide consists of a sugar, a phosphate group and a nitrogenous base. The polymer has a sugar-phosphate backbone with bases attached. IGCSE questions often ask you to compare these natural polymers with synthetic ones.

DNA（脱氧核糖核酸）也是一种缩合聚合物，由核苷酸单体形成。每个核苷酸包含一个糖、一个磷酸基团和一个含氮碱基。聚合物具有糖-磷酸主链，并连接着碱基。IGCSE题目常要求你将这些天然聚合物与合成聚合物进行比较。

10. Plastics and the Environment: Disposal and Recycling | 塑料与环境：处置与回收

Most addition polymers are non-biodegradable because they are made of saturated carbon chains that microorganisms cannot break down. This leads to long-term pollution in landfills and oceans. Incineration reduces bulk but can release toxic gases unless carefully controlled.

大多数加成聚合物不可生物降解，因为它们由饱和碳链构成，微生物无法分解。这导致了填埋场和海洋中的长期污染。焚烧可减少体积，但若控制不当会释放有毒气体。

Recycling involves melting and remoulding thermoplastics, but different plastics must be sorted by type. Thermosets cannot be recycled by re-melting. Another approach is to develop biodegradable polymers, such as poly(lactic acid) from corn starch, which can be broken down by bacteria.

回收涉及将热塑性塑料熔融再塑形，但不同塑料必须按类型分拣。热固性塑料无法通过重熔回收。另一种方法是开发可生物降解的聚合物，如由玉米淀粉制成的聚乳酸，可被细菌分解。

Feedstock recycling breaks polymers back into monomers, which can then be re-polymerised. This is chemically challenging but could close the loop on plastic waste. In your exam, you may be asked to evaluate different disposal methods, weighing advantages against environmental harm.

原料回收法将聚合物分解回单体，然后重新聚合。这在化学上具有挑战性，但有可能闭合塑料废弃物的循环。考试中可能要求你评价不同处置方法，权衡其优点与环境危害。

11. Exam Tips and Common Pitfalls | 考试技巧与常见误区

When drawing repeat units, ensure the horizontal bonds extend outside the brackets so the chain can continue. For addition polymers, show no double bonds inside the repeat unit. In condensation polymerisation, remember to include the small molecule, usually H₂O, that is eliminated.

绘制重复单元时，确保水平键延伸到括号外，以表示链的延续。对于加成聚合物，重复单元内不能出现双键。在缩合聚合中，记得写出脱去的小分子，通常是H₂O。

A typical error is writing the monomer as CH₂— ensation polymers, do not confuse ester links with amide links; the question will provide the functional groups, so copy them accurately.

一个典型错误是将单体写成CH₂—CH₂而不是CH₂=CH₂。单体必须保留其官能团，即烯烃中的C=C双键。对于缩合聚合物，不要混淆酯键和酰胺键；题目会提供官能团，应准确照搬。

Use the correct terminology: 'addition polymerisation' involves only one product – the polymer itself, while 'condensation polymerisation' yields a polymer plus a small molecule. These precise phrases earn marks in structured questions. Finally, always link the structure of a polymer to its properties and uses when asked to explain.

使用正确的术语：“加成聚合”只生成一种产物——聚合物本身，而“缩合聚合”生成聚合物外加一个小分子。在结构化题目中，这些精确的表述能赢得分数。最后，当要求解释时，始终将聚合物的结构与其性质和用途联系起来。

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