Polymers in IGCSE WJEC Chemistry | IGCSE WJEC 化学：聚合物考点精讲

📚 Polymers in IGCSE WJEC Chemistry | IGCSE WJEC 化学：聚合物考点精讲

Polymers are among the most important materials in modern life, from plastic bottles to proteins in our bodies. In IGCSE WJEC Chemistry, the topic of polymers covers addition and condensation polymerisation, the relationship between structure and properties, natural and synthetic polymers, and their environmental impact. This article will guide you through every key concept, equation, and exam tip you need to master this unit.

聚合物是现代生活中最重要的材料之一，从塑料瓶到体内的蛋白质。在 IGCSE WJEC 化学中，聚合物这一主题涵盖加成聚合与缩合聚合、结构与性质的关系、天然与合成聚合物以及它们对环境的影响。本文将带你逐一攻克每个关键概念、方程式和考试技巧，帮助你完全掌握本单元。

1. What are Polymers? | 什么是聚合物？

A polymer is a large molecule made by joining together many small repeating units called monomers. The process of linking monomers to form a polymer is called polymerisation. Polymers can be synthetic, like poly(ethene) and nylon, or natural, like proteins, starch, and cellulose.

聚合物是由许多称为单体的小重复单元连接而成的大分子。单体连接成聚合物的过程称为聚合反应。聚合物可以是合成的，如聚乙烯和尼龙，也可以是天然的，如蛋白质、淀粉和纤维素。

The name of a polymer is often formed by placing ‘poly’ in front of the monomer name, e.g. ethene becomes poly(ethene). In IGCSE, you must recognise the repeating unit and deduce the monomer, or vice versa.

聚合物的命名通常在单体名称前加上“聚”，例如乙烯变成聚乙烯。在 IGCSE 中，你必须能识别重复单元并推断单体，或者反过来。

Monomer: a small molecule that can join with many others.
单体：可以与其他分子连接的小分子。
Polymer: a long chain molecule built from many monomers.
聚合物：由许多单体制成的长链分子。
Repeating unit: the smallest group of atoms that repeats along the chain.
重复单元：沿链重复的最小原子团。

2. Addition Polymerisation | 加成聚合

Addition polymerisation occurs when unsaturated monomers containing C=C double bonds open up and join together to form a saturated polymer chain. No other product is formed. The conditions for addition polymerisation are high pressure and a catalyst, but for IGCSE you mainly need to draw the reaction and write equations.

加成聚合发生在含有 C=C 双键的不饱和单体打开并连接形成饱和聚合物链时。没有其他产物生成。加成聚合的条件是高压和催化剂，但对 IGCSE 来说，你主要需要会画反应并写出方程式。

For example, the polymerisation of ethene:

例如，乙烯的聚合：

n CH₂=CH₂ → –(CH₂–CH₂)–ₙ

The double bond in each monomer breaks, and the carbon atoms form single bonds with neighbouring monomers, producing a long alkane-like chain. The polymer name is poly(ethene) or polythene, used for plastic bags and bottles.

每个单体中的双键断裂，碳原子与相邻单体形成单键，产生长的类烷烃链。聚合物名称为聚乙烯，用于塑料袋和瓶子。

Similarly, propene polymerises to poly(propene):

类似地，丙烯聚合成聚丙烯：

n CH₃CH=CH₂ → –(CH(CH₃)–CH₂)–ₙ

When drawing addition polymers, you must show the repeating unit in brackets with extending bonds going through the brackets, and a subscript ‘n’ to indicate many repeats.

在绘制加成聚合物时，你必须将重复单元放在括号中，扩展键穿过括号，并用下标’n’表示许多重复。

3. Condensation Polymerisation | 缩合聚合

Condensation polymerisation involves monomers reacting together and releasing a small molecule, usually water or hydrogen chloride, each time a link is formed. The monomers must have two functional groups – one at each end. Common condensation polymers include polyesters, polyamides (nylons), and polypeptides (proteins).

缩合聚合涉及单体相互反应，每次形成连接时释放一个小分子，通常是水或氯化氢。单体必须有两个官能团——每端各一个。常见的缩合聚合物包括聚酯、聚酰胺（尼龙）和多肽（蛋白质）。

For example, a diol and a dicarboxylic acid form a polyester with the elimination of water:

例如，二醇和二羧酸形成聚酯并消去水：

n HO–R–OH + n HOOC–R’–COOH → –(O–R–OOC–R’–CO)–ₙ + 2n H₂O

Here, the ester linkage (–COO–) is the characteristic bond holding the polymer together. Nylon is a polyamide, formed from a diamine and a dicarboxylic acid, releasing water. The amide linkage (–CONH–) is key.

这里，酯键（–COO–）是保持聚合物结构的特征键。尼龙是一种聚酰胺，由二胺和二羧酸形成，释放水。酰胺键（–CONH–）是关键。

In IGCSE WJEC, you may need to draw parts of the polymer chain for condensation polymers, showing how the monomers join and identifying the small molecule lost. Remember that natural polymers like DNA and starch are also condensation polymers.

在 IGCSE WJEC 中，你可能需要画出缩合聚合物链的部分结构，展示单体如何连接并指明失去的小分子。记住像 DNA 和淀粉这样的天然聚合物也是缩合聚合物。

4. Drawing and Identifying Polymers | 绘制和识别聚合物

Exam questions often ask you to draw the repeating unit of a polymer given the monomer, or to identify the monomer from a section of the polymer chain. For addition polymers, you reverse the polymerisation: remove the brackets and add back the double bond between the carbon atoms that were joined.

考试题目经常要求根据给定的单体画出聚合物的重复单元，或者从一段聚合物链中识别单体。对于加成聚合物，逆向操作：去掉括号，并在原本相连的碳原子之间加回双键。

Key steps for deducing an addition monomer:

Identify the repeating unit – two carbon atoms in the backbone with any side groups.
辨识重复单元——主链上的两个碳原子及其侧基。
Draw the two carbon atoms connected by a double bond and arrange side groups accordingly.
画出以双键连接的两个碳原子，并相应排列侧基。
Ensure each carbon atom still forms four bonds.
确保每个碳原子仍形成四个键。

For condensation polymers, you break the chain at the functional linkage (ester or amide) and add back the small molecule (water) to regenerate the monomer functional groups (e.g. –OH and –COOH).

对于缩合聚合物，在官能团连接处（酯键或酰胺键）断开，再加回小分子（水）以恢复单体的官能团（如 –OH 和 –COOH）。

5. Types of Polymers: Thermoplastics and Thermosets | 聚合物种类：热塑性与热固性

Polymers can be classified based on their behaviour when heated. This is directly linked to their structure and bonding.

聚合物可根据加热时的行为进行分类。这直接与其结构和键合有关。

Thermoplastics \| 热塑性	Thermosets \| 热固性
Soften when heated and harden when cooled; can be reshaped.	Do not soften when heated; char or burn instead.
加热时软化，冷却时硬化；可重新塑形。	加热时不软化，反而焦化或燃烧。
Consist of linear or branched chains with weak intermolecular forces between them, which are overcome on heating.	Have strong covalent cross-links between chains, locking the structure.
由线性或支化链组成，链间分子间作用力较弱，加热时被克服。	链间有强共价交联，锁住结构。
Examples: poly(ethene), poly(propene), PVC.	Examples: bakelite, melamine, vulcanised rubber.
例：聚乙烯、聚丙烯、PVC。	例：电木、三聚氰胺、硫化橡胶。

Understanding this distinction is important for choosing materials for specific applications, e.g. electric plugs (thermoset) vs plastic bags (thermoplastic).

理解这种区别对于为特定应用选择材料很重要，例如电插头（热固性）与塑料袋（热塑性）。

6. Natural Polymers | 天然聚合物

Nature produces a vast array of polymers essential for life. Proteins, carbohydrates (starch, cellulose, glycogen), and nucleic acids (DNA, RNA) are all condensation polymers. For IGCSE, you should know the basic building blocks.

自然界产生了大量对生命至关重要的聚合物。蛋白质、碳水化合物（淀粉、纤维素、糖原）和核酸（DNA、RNA）都是缩合聚合物。在 IGCSE 中，你应该了解它们的基本构建单元。

Proteins are polyamides made from amino acid monomers. Amino acids contain both amine (–NH₂) and carboxylic acid (–COOH) groups. They condense, releasing water, to form peptide bonds.

蛋白质是由氨基酸单体制成的聚酰胺。氨基酸同时含有胺基（–NH₂）和羧酸基（–COOH）。它们缩合释放水，形成肽键。

Starch and cellulose are polysaccharides, polymers of glucose. Glucose molecules join by glycosidic bonds in a condensation reaction, with water lost. The arrangement of glucose units differs, giving different properties (e.g. cellulose is fibrous and strong, starch is a storage molecule).

淀粉和纤维素是多糖，是葡萄糖的聚合物。葡萄糖分子通过糖苷键在缩合反应中连接，失去水。葡萄糖单元的排列方式不同，导致性质不同（例如，纤维素呈纤维状且坚固，淀粉是储存分子）。

DNA is a condensation polymer of nucleotides, each consisting of a sugar, a phosphate group, and a nitrogenous base. The phosphate-sugar backbone is formed by condensation.

DNA 是核苷酸的缩合聚合物，每个核苷酸由糖、磷酸基团和含氮碱基组成。磷酸-糖骨架是通过缩合形成的。

7. Synthetic Polymers and Their Uses | 合成聚合物及其用途

The IGCSE syllabus expects you to link common polymers to their properties and everyday uses. Below is a summary table of key examples:

IGCSE 课程要求你将常见聚合物与其性质和日常用途联系起来。下面是一些关键示例的总结表：

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	Plastic bags, bottles, cling film
聚丙烯 (PP)	Propene \| 丙烯	Tough, resists cracking	Rope, carpets, crates
PVC \| 聚氯乙烯	Chloroethene \| 氯乙烯	Hard (unplasticised) or flexible (plasticised), fire-resistant	Pipes, window frames, electrical insulation
PTFE (Teflon) \| 聚四氟乙烯	Tetrafluoroethene \| 四氟乙烯	Very slippery, heat-resistant, non-stick	Non-stick pans, bearings, waterproof clothing
Nylon \| 尼龙	Diamine + dicarboxylic acid	Strong, elastic, abrasion-resistant	Ropes, clothing, parachutes
Polyester \| 聚酯	Diol + dicarboxylic acid	Crease-resistant, dries quickly	Clothing, bottles, films

8. Properties and Structure Relationship | 性质与结构的关系

The properties of a polymer depend on its chain length, branching, cross-linking, and the strength of intermolecular forces or covalent bonds between chains. Shorter chains result in a lower melting point and more flexibility, as there are fewer van der Waals forces.

聚合物的性质取决于其链长、支化度、交联度以及链间的分子间作用力或共价键的强度。较短的链导致较低的熔点和更大的柔韧性，因为范德瓦尔斯力较少。

Crystalline regions where chains pack closely increase density and stiffness, while amorphous regions give flexibility. Polymers with bulky side groups, like poly(propene), have weaker interchain attractions and thus lower softening temperatures than poly(ethene) in some forms.

链紧密排列的结晶区域会增加密度和刚度，而非晶区域则提供柔韧性。带有庞大侧基的聚合物，如聚丙烯，链间吸引力较弱，因此某些形式的软化温度低于聚乙烯。

Cross-linking drastically changes properties. Vulcanised rubber is an elastomer with sulfur cross-links; it returns to its original shape after stretching. Thermosetting polymers have very extensive cross-linking, making them hard and infusible.

交联会显著改变性质。硫化橡胶是一种弹性体，有硫交联；拉伸后可恢复原状。热固性聚合物具有非常广泛的交联，使它们坚硬且不可熔化。

9. Environmental Impact of Polymers | 聚合物的环境影响

Many synthetic polymers are non-biodegradable, meaning they persist in the environment for hundreds of years. This leads to problems such as litter, harm to wildlife, and microplastic pollution. Additionally, the production of polymers relies on finite crude oil resources and consumes energy, contributing to carbon dioxide emissions.

许多合成聚合物不可生物降解，这意味着它们会在环境中存留数百年。这会导致垃圾污染、危害野生动物以及微塑料污染等问题。此外，聚合物的生产依赖有限的原油资源并消耗能源，导致二氧化碳排放。

However, polymers also have positive environmental aspects: they are lightweight, reducing transport fuel consumption, and durable, which extends product life. The challenge is to manage plastic waste responsibly.

然而，聚合物也有积极的环保方面：它们重量轻，可减少运输燃料消耗，且耐用，延长了产品寿命。挑战在于负责任地管理塑料废物。

Key terms to know: ‘biodegradable’ means capable of being broken down by microorganisms; ‘non-biodegradable’ means resistant to natural decay processes.

需要了解的关键术语：“可生物降解”指能被微生物分解；“不可生物降解”指能抵抗自然腐败过程。

10. Disposal and Recycling | 处理与回收

The WJEC specification expects you to discuss ways of disposing of polymers and their advantages and disadvantages.

Landfill: cheap but takes up space and wastes resources; non-biodegradable plastics remain indefinitely.
填埋：便宜，但占用空间并浪费资源；不可生物降解的塑料会无限期存留。
Incineration: reduces volume and can generate electricity; but can release toxic gases (e.g. HCl from PVC) unless properly treated, and produces CO₂.
焚烧：减少体积并可发电；但若处理不当会释放有毒气体（如 PVC 的 HCl），并产生 CO₂。
Recycling: conserves resources and reduces landfill, but collection, sorting and cleaning are labour-intensive and costly. Different polymers must be separated, as mixed polymers produce poor-quality recycled material.
回收：节约资源并减少填埋，但收集、分类和清洗劳动密集且成本高。不同聚合物必须分开，因为混合聚合物会产生劣质回收材料。
Chemical recycling/feedstock recycling: breaking polymers back into monomers or fuel; still under development.
化学回收/原料回收：将聚合物分解回单体或燃料，仍在发展中。

Students should be able to evaluate these methods using evidence, and suggest how life cycle assessments can be used to choose the best disposal route.

学生应能利用证据评估这些方法，并建议如何使用生命周期评估来选择最佳的处理途径。

11. Biodegradable Polymers | 生物降解聚合物

To combat plastic pollution, chemists have developed biodegradable polymers. Some are made from renewable plant materials, such as polylactic acid (PLA) from corn starch, and polyhydroxybutyrate (PHB) produced by bacteria. These polymers can be broken down by microorganisms into water, carbon dioxide, and biomass under suitable conditions.

为了对抗塑料污染，化学家们开发了可生物降解的聚合物。有些由可再生植物材料制成，例如来自玉米淀粉的聚乳酸（PLA），以及由细菌产生的聚羟基丁酸酯（PHB）。这些聚合物在适宜条件下可被微生物分解为水、二氧化碳和生物质。

Nevertheless, biodegradable plastics often require specific composting conditions (high temperature, moisture) to degrade effectively, and they are not a simple ‘throw-away’ solution. They can also contaminate conventional plastic recycling streams.

然而，可生物降解塑料通常需要特定的堆肥条件（高温、湿度）才能有效降解，它们并不是简单的“一扔了之”的解决方案。它们还可能污染传统的塑料回收流。

Other approaches include oxo-biodegradable plastics, which contain additives that promote fragmentation, but these may lead to microplastic formation before full breakdown.

其他方法包括氧化生物降解塑料，它们含有促进碎裂的添加剂，但这可能导致在完全分解前形成微塑料。

12. Exam Tips and Common Mistakes | 考试技巧与常见错误

Here are some targeted tips for IGCSE WJEC polymer questions:

以下是一些针对 IGCSE WJEC 聚合物题目的技巧：

Always show the repeating unit with brackets and extending bonds through the brackets. Many students lose marks by forgetting to show continuation bonds outside.
始终用括号和穿过括号的延伸键表示重复单元。许多学生因忘记在括号外显示延续键而丢分。
For addition polymerisation, check that there are no C=C double bonds in the polymer backbone; the product is fully saturated.
对于加成聚合，检查聚合物主链中没有 C=C 双键；产物是完全饱和的。
In condensation polymerisation, do not forget to show the small molecule (like water) on the product side of the equation.
在缩合聚合中，不要忘记在方程式的产物侧写出小分子（如水）。
When linking properties to uses, mention both the property and the need it fulfills, e.g. ‘PTFE is non-stick and heat-resistant, so it is used for coating frying pans.’
在将性质与用途联系起来时，要同时提及性质和它满足的需求，例如“PTFE 不粘且耐热，因此用于涂覆煎锅”。
Be specific about disposal problems: ‘PVC releases toxic hydrogen chloride gas when burned’ is better than ‘burning is bad’.
关于处理问题要具体：“PVC 燃烧时释放有毒的氯化氢气体”比“燃烧不好”更好。
Practice identifying monomers from given polymer sections, especially for condensation polymers, by recognising ester or amide links and adding water back.
练习从给定的聚合物片段中识别单体，特别是缩合聚合物，通过识别酯键或酰胺键并加回水。

Revision should include drawing the formation of terylene (polyester) and nylon 6,6 as specific examples, as they often appear in WJEC papers.

复习时应包括绘制涤纶（聚酯）和尼龙 6,6 的形成作为具体例子，因为它们常出现在 WJEC 试卷中。

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Polymers in IGCSE WJEC Chemistry | IGCSE WJEC 化学：聚合物 考点精讲