Polymers for IB and WJEC Chemistry | IB WJEC 化学：聚合物 考点精讲

📚 Polymers for IB and WJEC Chemistry | IB WJEC 化学：聚合物 考点精讲

Polymers are the molecular giants that shape our daily lives—from the proteins in our bodies to the plastics in our phones. In both IB and WJEC chemistry, the topic of polymers bridges organic chemistry with real‑world applications, demanding a clear understanding of structure, synthesis, and sustainability. This article distils the essential concepts and exam‑ready facts, presented in paired English‑Chinese explanations to support bilingual learners.

聚合物是塑造我们日常生活的分子巨人——从我们体内的蛋白质到手机中的塑料。在IB和WJEC化学中，聚合物专题将有机化学与现实应用紧密相连，要求考生清晰理解结构、合成和可持续性。本文提炼了核心概念和应试要点，以英中双语对照讲解，助力双语学习者。

1. What Are Polymers? | 什么是聚合物？

Polymers are large molecules (macromolecules) built from many repeating small units called monomers. The process of joining monomers together is polymerisation. Polymers can be natural, like cellulose and proteins, or synthetic, like polyethylene and nylon. Both IB and WJEC syllabuses stress the ability to recognise the repeating unit from a given polymer structure and vice versa.

聚合物是由许多称为单体的小单元重复连接而成的大分子（高分子）。将单体连接起来的过程叫做聚合反应。聚合物可以是天然的，如纤维素和蛋白质，也可以是合成的，如聚乙烯和尼龙。IB和WJEC大纲都强调从给定的聚合物结构中识别重复单元的能力，以及反过来从重复单元推导聚合物结构。

2. Addition Polymerisation | 加成聚合

Addition polymerisation occurs when unsaturated monomers (containing C=C bonds) join together without the loss of any atoms. The double bond opens up, and monomers add to the growing chain. Common examples include poly(ethene) from ethene, poly(propene) from propene, and PVC from chloroethene. The repeating unit has exactly the same atoms as the monomer. You must be able to draw the polymer given the monomer, using displayed formulas with square brackets and n denoting many repeats.

加成聚合发生在不饱和单体（含有C=C双键）之间，单体连接时不失去任何原子。双键打开，单体逐一添加到增长的链上。常见例子有乙烯聚合为聚乙烯，丙烯聚合为聚丙烯，氯乙烯聚合为聚氯乙烯。重复单元的原子组成与单体完全相同。考生必须能够根据单体画出聚合物的结构，使用展示式，并用方括号和n表示多个重复单元。

3. Condensation Polymerisation | 缩合聚合

Condensation polymerisation involves monomers with two functional groups, often releasing a small molecule such as water or HCl when they join. Polyesters form from dicarboxylic acids and diols, with ester linkages (–COO–). Polyamides (nylons) form from dicarboxylic acids and diamines, with amide linkages (–CONH–). Kevlar is a notable aromatic polyamide. In IB, you need to identify the two monomer types from a polymer chain, while WJEC also expects the drawing of repeating units and the identification of the small molecule eliminated.

缩合聚合涉及含有两个官能团的单体，通常会在连接时释放出一个水分子或HCl等小分子。聚酯由二羧酸和二醇生成，含有酯基（–COO–）。聚酰胺（尼龙）由二羧酸和二胺生成，含有酰胺键（–CONH–）。凯芙拉（Kevlar）是一种重要的芳香族聚酰胺。在IB中，你需要从聚合物链中识别两种单体类型；WJEC则还要求画出重复单元并确定离去的小分子。

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

Thermoplastics soften when heated and harden upon cooling; this process is reversible because the polymer chains are held by weak intermolecular forces without cross‑linking. Examples include poly(ethene), poly(propene), and PVC. Thermosets, however, have strong covalent cross‑links between chains, making them rigid and non‑meltable. Once set, they cannot be reshaped—Bakelite and epoxy resins are typical examples. WJEC exams often ask you to relate the property differences to structure and bonding.

热塑性塑料加热软化、冷却变硬；此过程可逆，因为聚合物分子链之间仅靠微弱的分子间作用力结合，无交联。例如聚乙烯、聚丙烯和PVC。而热固性塑料在分子链间存在强共价交联，使其坚硬且不可熔化。一旦成型便无法重塑——酚醛树脂（Bakelite）和环氧树脂即为典型例子。WJEC考试常要求将性质差异与结构和键合方式联系起来。

A comparison table is often helpful for revision:

复习时一张对比表常很有用：

Property / 性质	Thermoplastic / 热塑性	Thermoset / 热固性
Effect of heat / 加热效果	Softens, melts / 软化、熔化	Does not melt; char / 不熔，焦化
Cross‑linking / 交联	No / 无	Extensive covalent cross‑links / 大量共价交联
Recycling / 回收	Can be remoulded / 可重塑	Difficult; usually ground for filler / 困难；通常研磨作填料
Examples / 例子	PE, PP, PVC, PS / 聚乙烯、聚丙烯等	Bakelite, melamine, epoxy / 酚醛、三聚氰胺、环氧

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5. Natural Polymers | 天然聚合物

Nature provides remarkable polymers. Polypeptides (proteins) are condensation polymers of amino acids linked by peptide bonds (–CONH–). Polysaccharides include starch, cellulose, and glycogen, all built from glucose monomers but differing in the type of glycosidic linkage and chain branching. DNA and RNA are polynucleotides—condensation polymers of nucleotides. IB expects you to know the basic structures, whereas WJEC may focus on proteins and carbohydrates in the context of condensation polymerisation.

大自然提供了非凡的聚合物。多肽（蛋白质）是由氨基酸通过肽键（–CONH–）缩合而成的聚合物。多糖包括淀粉、纤维素和糖原，均由葡萄糖单体构成，区别在于糖苷键类型和链的分支程度不同。DNA和RNA是多核苷酸——由核苷酸缩合而成的聚合物。IB要求掌握基本结构；WJEC则可能结合缩合聚合考查蛋白质和碳水化合物。

6. Synthetic Polymers: Naming and Uses | 合成聚合物的命名与用途

You should be familiar with common addition and condensation polymers. For addition: poly(ethene) – plastic bags, bottles; poly(propene) – ropes, carpets; poly(chloroethene) (PVC) – window frames, pipes; poly(tetrafluoroethene) (PTFE) – non‑stick coatings. For condensation: polyesters – clothing fibres (Terylene), bottles; polyamides – nylon ropes, Kevlar bullet‑proof vests. IB questions may ask you to deduce the monomer(s) given a section of the polymer chain, while WJEC may set problems on properties matching uses.

你应该熟悉常见的加成聚合物和缩合聚合物。加成类：聚乙烯——塑料袋、瓶子；聚丙烯——绳索、地毯；聚氯乙烯（PVC）——窗框、管道；聚四氟乙烯（PTFE）——不粘涂层。缩合类：聚酯——服装纤维（涤纶）、瓶子；聚酰胺——尼龙绳索、凯芙拉防弹衣。IB考题可能给你一段聚合物链要求推导单体；WJEC可能设置性质与用途匹配的问题。

7. Polymerisation Equations | 聚合反应方程式

Writing polymerisation equations correctly is a core skill. For addition polymerisation:

n CH₂=CH₂ → –[CH₂–CH₂]ₙ–

For condensation polymerisation, show the repeating unit and the eliminated small molecule. Example of a polyester from ethane‑1,2‑diol and terephthalic acid:

n HO–CH₂CH₂–OH + n HOOC–C₆H₄–COOH → –[O–CH₂CH₂–OOC–C₆H₄–CO]ₙ– + (2n-1)H₂O

Note that IB often uses a simplified approach where exactly n water molecules are eliminated if the polymer chain is drawn as having n repeating units and ignoring end groups. Always balance your equations and specify the state symbols when required.

正确书写聚合反应方程式是核心技能。对加成聚合：n CH₂=CH₂ → –[CH₂–CH₂]ₙ–。对缩合聚合，要展示重复单元和离去的小分子。以乙二醇和对苯二甲酸形成的聚酯为例：n HO–CH₂CH₂–OH + n HOOC–C₆H₄–COOH → –[O–CH₂CH₂–OOC–C₆H₄–CO]ₙ– + (2n-1)H₂O。注意IB常采用简化方法：若聚合物含有n个重复单元并忽略端基，则恰好脱去n个水分子。务必配平方程式，并在要求时注明物态符号。

8. Physical Properties and Intermolecular Forces | 物理性质与分子间力

The mechanical properties of polymers depend on chain length, branching, cross‑linking, and the strength of intermolecular forces. Linear PE (HDPE) has stronger van der Waals forces due to close packing, making it rigid; branched PE (LDPE) is more flexible. Polyamides and polyesters can form hydrogen bonds between chains, giving high tensile strength and melting points. Thermosets owe their heat‑resistance to covalent cross‑links. IB often integrates these structure‑property relationships into Paper 1 and Paper 2 questions.

聚合物的力学性质取决于链长、支化度、交联程度以及分子间力的强度。线性聚乙烯（高密度聚乙烯，HDPE）因紧密堆积而具有更强的范德华力，质地坚硬；支化聚乙烯（低密度聚乙烯，LDPE）则更柔软。聚酰胺和聚酯能在链间形成氢键，因此具有高拉伸强度和较高熔点。热固性塑料的耐热性则归因于共价交联。IB常将这些结构—性质关系融入Paper 1和Paper 2的考题。

9. Degradation and Environmental Issues | 降解与环境问题

Most addition polymers are non‑biodegradable, persisting in the environment. Condensation polymers such as polyesters and polyamides can be hydrolysed, but the process is slow. Photodegradable plastics contain light‑sensitive additives that help break down the polymer in sunlight. Bioplastics, like PLA (polylactic acid) from corn starch, are derived from renewable resources and can biodegrade under industrial composting conditions. WJEC places particular emphasis on the problems of plastic waste and the potential solutions, including recycling and degradable alternatives.

大多数加成聚合物不可生物降解，在环境中持久存在。缩合聚合物如聚酯和聚酰胺能够水解，但过程缓慢。光降解塑料含有光敏添加剂，有助于在阳光下分解聚合物。生物塑料，如由玉米淀粉制得的聚乳酸（PLA），来源于可再生资源，可在工业堆肥条件下降解。WJEC尤其关注塑料废弃物问题及其潜在解决方案，包括回收和可降解替代品。

10. Recycling Methods and Identification Codes | 回收方法与识别码

Mechanical recycling involves sorting, grinding, melting, and remoulding; it suits thermoplastics. Chemical recycling breaks polymers back into monomers for repolymerisation. The resin identification codes (RIC) 1–7 help sort plastics: 1 PET, 2 HDPE, 3 PVC, 4 LDPE, 5 PP, 6 PS, 7 Other. Both IB and WJEC may reference these codes in data‑analysis questions. You should be able to discuss the advantages and limitations of recycling, including contamination and downcycling.

机械回收包括分拣、粉碎、熔融和重塑，适用于热塑性塑料。化学回收则把聚合物分解回单体，供再聚合使用。塑料识别码（RIC）1–7有助于分类：1 PET、2 HDPE、3 PVC、4 LDPE、5 PP、6 PS、7 其他。IB和WJEC均可能在数据分析题中引用这些编码。你应能讨论回收的优点和局限，包括污染问题和降级回收。

11. Key Practicals and Demonstrations | 关键实验与演示

Making nylon by interfacial polymerisation is a classic school experiment: a solution of a diamine in water is layered over a solution of a diacyl chloride in an organic solvent, and nylon forms as a film at the interface. This demonstrates condensation polymerisation vividly. The preparation of a polyester (e.g., from citric acid and glycerol) can also be shown. WJEC practical tasks may ask you to evaluate these syntheses, while IB’s internal assessment might involve investigating the properties of different polymers.

界面聚合制备尼龙是经典学校实验：将二胺水溶液覆于二酰氯的有机溶液上，尼龙便在界面以薄膜形式生成，生动地展示了缩合聚合。也可演示聚酯的制备（例如由柠檬酸和甘油制得）。WJEC实验任务可能要求评估这些合成过程，而IB的内部评估（IA）可能涉及探究不同聚合物的性质。

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

When drawing polymers, never forget the brackets, the n subscript, and the continuation bonds through the brackets. For condensation polymers, show the small molecule (usually H₂O or HCl) separately. In IB, be precise with the number of water molecules eliminated. In WJEC, make sure you can name the monomers using systematic names. Avoid confusing ester and amide linkages. Always link a polymer’s property, such as flexibility or high melting point, back to its structure and intermolecular forces. Finally, practise deducing monomers from both addition and condensation polymers, as this is a frequently examined skill.

画聚合物时，永远不要忘记方括号、下标n以及穿过方括号的延续键。对缩合聚合物，要单独画出离去的小分子（通常是H₂O或HCl）。在IB中，要精确处理脱去水分子的数目。在WJEC中，确保能用系统命名法命名单体。避免混淆酯基和酰胺键。始终将聚合物的性质（如柔韧性或高熔点）与结构和分子间力联系起来。最后，多加练习从加成和缩合聚合物推导单体的技能，这是高频考点。

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