Polymer Chemistry: Key Concepts for IB Edexcel | IB Edexcel 化学：聚合物考点精讲

📚 Polymer Chemistry: Key Concepts for IB Edexcel | IB Edexcel 化学：聚合物考点精讲

Polymers are giant molecules that underpin much of modern life, from plastic packaging to high‑performance textiles. In the IB and Edexcel chemistry specifications, the study of polymers covers both addition and condensation polymerisation, the relationship between structure and properties, and the environmental challenges posed by plastic waste. This article provides a focused revision guide, linking key definitions to exam‑style reasoning and calculations.

聚合物是构成现代生活诸多方面的高分子，从塑料包装到高性能纺织品。在 IB 和 Edexcel 化学考纲中，聚合物的学习涵盖加成聚合与缩合聚合、结构与性质的关系，以及塑料废弃物带来的环境挑战。本文提供一份重点复习指南，将关键定义与考试常见的推理和计算联系起来。

1. Introduction to Polymers | 聚合物简介

A polymer is a long‑chain molecule made up of many repeating units called monomers. The process of linking monomers together is polymerisation. Polymers can be natural, such as proteins and cellulose, or synthetic, such as poly(ethene) and nylon. The properties of a polymer depend on the type of monomer, the chain length, the degree of branching, and the intermolecular forces between chains.

聚合物是由许多称为单体的重复单元组成的长链分子。将单体连接起来的过程就是聚合反应。聚合物可以是天然的，如蛋白质和纤维素，也可以是合成的，如聚乙烯和尼龙。聚合物的性质取决于单体类型、链长、支化程度以及链间的分子间作用力。

There are two main classes of synthetic polymerisation: addition polymerisation and condensation polymerisation. In addition polymerisation, unsaturated monomers (typically alkenes) join together without the loss of any small molecule. In condensation polymerisation, monomers with two functional groups react, eliminating a small molecule such as water or hydrogen chloride for each new bond formed.

合成聚合主要有两类：加成聚合和缩合聚合。在加成聚合中，不饱和单体（通常为烯烃）直接连接，没有小分子脱落。在缩合聚合中，带有两个官能团的单体发生反应，每生成一个化学键便脱去一个小分子，如水或氯化氢。

2. Addition Polymerisation | 加成聚合

Addition polymerisation requires monomers that contain a carbon–carbon double bond (C=C). Under high pressure, elevated temperature, and the influence of a suitable catalyst, the π bond of the alkene breaks open, allowing each monomer to form two new σ bonds with neighbouring monomers. The reaction is a free‑radical mechanism. Initiation generates radicals from an initiator (e.g., an organic peroxide), propagation builds the chain, and termination stops growth when two radicals combine or disproportionate.

加成聚合要求单体含有碳碳双键 (C=C)。在高压、高温及合适催化剂的作用下，烯烃的 π 键断裂，每个单体与相邻单体形成两个新的 σ 键。反应遵循自由基机理：引发剂（如有机过氧化物）产生自由基引发反应，链增长构建长链，两个自由基结合或歧化时发生链终止。

n CH₂=CH₂ → —(CH₂—CH₂)—ₙ

The polymer is the only product; no atoms are lost. The empirical formula of the polymer is the same as that of the monomer. The backbone of the chain is made of carbon–carbon single bonds, and there may be side groups depending on the substituted alkene used. For instance, poly(propene) has a –CH₃ side group on every other carbon atom.

聚合物是唯一的产物，没有原子损失。聚合物的最简式与单体相同。链的主骨架由碳碳单键构成，若使用取代烯烃，则可能存在侧基。例如，聚丙烯每隔一个碳原子就有一个 –CH₃ 侧基。

3. Common Addition Polymers | 常见的加成聚合物

Several addition polymers are named directly in the IB and Edexcel specifications. They appear in questions about naming, structure, and properties.

IB 和 Edexcel 考纲中明确提到几种加成聚合物，常出现在关于命名、结构和性质的问题中。

Poly(ethene) – from ethene; used for plastic bags, bottles; low‑density (LDPE) has branched chains, high‑density (HDPE) has linear chains, giving different flexibility and strength.
聚(乙烯) – 由乙烯制得；用于塑料袋、瓶子；低密度聚乙烯 (LDPE) 有支链，高密度聚乙烯 (HDPE) 为线型链，柔韧性和强度不同。
Poly(propene) – from propene; used for ropes, carpets, car bumpers; methyl side group makes it stiffer and with a higher melting point than poly(ethene).
聚(丙烯) – 由丙烯制得；用于绳索、地毯、汽车保险杠；甲基侧基使其比聚乙烯更硬、熔点更高。
Poly(chloroethene) (PVC) – from chloroethene; rigid when unplasticised (uPVC) for window frames, flexible with plasticisers for cables.
聚(氯乙烯) (PVC) – 由氯乙烯制得；未增塑时 (uPVC) 坚硬，用于窗框；增塑后柔软，用于电缆。
Poly(tetrafluoroethene) (PTFE, Teflon) – highly unreactive due to strong C–F bonds; non‑stick coatings.
聚(四氟乙烯) (PTFE, 特氟龙) – 因 C–F 键强而极不活泼；用于不粘涂层。
Poly(styrene) – from styrene (phenylethene); transparent, brittle; used in packaging, insulating foam when expanded.
聚(苯乙烯) – 由苯乙烯（苯基乙烯）制得；透明、脆性；发泡后用作包装和绝缘泡沫。

Be able to draw a short section of the polymer chain from a given monomer, and vice versa. The repeat unit must be shown with brackets and a subscript ‘n’.

要能根据给定单体画出聚合物短链段的重复单元，反之亦然。重复单元必须用方括号和下标 n 表示。

4. Condensation Polymerisation | 缩合聚合

Condensation polymerisation occurs when monomers with two functional groups – one on each end – react together, forming a polymer and releasing a small molecule as a by‑product. The most common by‑products are water (from ester and amide links) and hydrogen chloride (from acyl chloride reactions). Each monomer must have a functional group that can react with the functional group of another monomer.

缩合聚合发生在每个单体两端各带一个官能团的情况下，它们相互反应生成聚合物，同时脱去一个小分子副产物。最常见的副产物是水（由酯键和酰胺键生成）以及氯化氢（酰氯反应）。每个单体必须具有能与另一单体官能团反应的官能团。

Types of condensation polymers include polyesters (ester links), polyamides (amide links), and polycarbonates. The repeating unit of a condensation polymer is not a simple copy of the monomer; it varies because the small molecule is lost. When drawing repeat units, clearly show the ester or amide linkage and indicate the loss of water with the formula.

缩合聚合物的类型包括聚酯（酯键）、聚酰胺（酰胺键）和聚碳酸酯。缩聚物的重复单元并非单体的简单复制，因为脱去了小分子。画重复单元时，必须清楚显示酯键或酰胺键，并在化学方程式中标明脱去的水。

5. Polyesters | 聚酯

Polyesters are formed by the reaction between a dicarboxylic acid (or its acyl chloride) and a diol. The most famous example is Terylene (polyethylene terephthalate, PET), made from benzene‑1,4‑dicarboxylic acid and ethane‑1,2‑diol. During the reaction, an ester link (–COO–) forms and water is eliminated.

聚酯由二元羧酸（或其酰氯）与二元醇反应生成。最著名的例子是特丽丝（聚对苯二甲酸乙二醇酯，PET），由苯‑1,4‑二甲酸和乙‑1,2‑二醇制得。反应中生成酯键 (–COO–) 并脱去水。

n HOOC–C₆H₄–COOH + n HO–CH₂CH₂–OH → —[OC–C₆H₄–COO–CH₂CH₂–O]—ₙ + (2n-1) H₂O

Alternatively, an acyl chloride such as ethanedioyl dichloride can react with a diol, releasing HCl instead of water. PET is widely used in drinks bottles and synthetic fibres. Its polar ester groups enable dye pickup and allow it to be melt‑blown or drawn into fibres. The repeat unit for PET is –[OC–C₆H₄–COO–CH₂CH₂–O]–.

也可以使用二元酰氯，如草酰氯与二元醇反应，此时脱去的是氯化氢而非水。PET 广泛用于饮料瓶和合成纤维。其极性酯基使纤维易于染色，并能熔喷或拉伸成丝。PET 的重复单元为 –[OC–C₆H₄–COO–CH₂CH₂–O]–。

6. Polyamides | 聚酰胺

Polyamides contain the amide (peptide) link –CONH–. They are formed from a dicarboxylic acid (or diacyl chloride) and a diamine. Nylon‑6,6 is the classic example, made from hexanedioic acid (adipic acid) and 1,6‑diaminohexane (hexamethylenediamine). Each link eliminates a water molecule.

聚酰胺含有酰胺键（肽键）–CONH–。它们由二元羧酸（或二酰氯）与二元胺生成。尼龙‑6,6 是经典例子，由己二酸和 1,6‑二氨基己烷（己二胺）制成。每生成一个酰胺键脱去一分子水。

n H₂N–(CH₂)₆–NH₂ + n HOOC–(CH₂)₄–COOH → —[HN–(CH₂)₆–NHOC–(CH₂)₄–CO]—ₙ + (2n-1) H₂O

Nylon‑6,6 has strong intermolecular hydrogen bonds between the N–H of one chain and the C=O of a neighbouring chain, giving it high tensile strength and a high melting point. Another important polyamide is Kevlar, which uses aromatic monomers to achieve extremely high strength for bullet‑proof vests.

尼龙‑6,6 链间的 N–H 与相邻链的 C=O 之间形成强的分子间氢键，使其具有高拉伸强度和高熔点。另一种重要的聚酰胺是凯夫拉 (Kevlar)，使用芳香族单体以获得极高强度，用于防弹衣。

When drawing repeat units for polyamides, ensure the amide group is shown correctly between the carbon chains, and the water lost is indicated in the stoichiometry.

在绘制聚酰胺的重复单元时，要确保酰胺基团正确显示在碳链之间，并在计量关系中标明脱去的水。

7. Comparing Addition and Condensation Polymers | 加成与缩合聚合物的比较

A clear understanding of the differences between the two polymerisation types is crucial for exams. The following table highlights the key contrasts.

清晰理解两种聚合类型的区别对考试至关重要。下表突出了关键对比。

Feature	Addition polymerisation	Condensation polymerisation
Monomer requirement	Contains C=C double bond	Two functional groups per monomer (e.g., –COOH and –OH, or –COOH and –NH₂)
By‑product	None	Small molecule (usually H₂O or HCl)
Backbone	Carbon atoms only	Contains heteroatoms (O, N) in main chain
Empirical formula	Same as monomer	Differs from monomer due to loss of small molecule
Degradability	Generally non‑biodegradable (except some with biodegradable additives)	Often biodegradable (e.g., polyesters and polyamides can be hydrolysed)
Examples	Poly(ethene), PVC, PTFE, polystyrene	PET, nylon‑6,6, Kevlar

When identifying a polymerisation type from a given equation or diagram, first check whether a small molecule is eliminated. If not, and the monomer is an alkene, it is addition. If water or HCl is given as a product, and there are two different functional groups in the monomer(s), it is condensation.

从给定的方程式或示意图判断聚合类型时，首先检查是否脱去小分子。若没有小分子脱去且单体为烯烃，则为加成聚合。若有水或氯化氢作为产物，且单体（或两种单体）带有两种不同的官能团，则为缩合聚合。

8. Thermoplastics and Thermosets | 热塑性塑料与热固性塑料

Polymers can be classified by their response to heat. Thermoplastics soften on heating and harden on cooling; this process is reversible. They consist of linear or branched chains that are not cross‑linked, so the intermolecular forces can be overcome by heat, allowing chains to slide past each other. Examples include poly(ethene), PVC, and polystyrene. Thermoplastics can be remoulded and recycled.

聚合物可按其对热的响应分类。热塑性塑料受热软化、冷却变硬，该过程可逆。它们由无交联的线型或支化链组成，分子间作用力可被热量克服，使链之间相互滑移。例子包括聚乙烯、PVC 和聚苯乙烯。热塑性塑料可重塑和回收。

Thermosets, in contrast, are irreversibly hardened by heat. They form extensive covalent cross‑links between polymer chains during curing, creating a rigid three‑dimensional network. Once set, they cannot be remelted – further heating only causes decomposition. Examples include epoxy resins, vulcanised rubber, and melamine. Thermosets are typically stronger and more heat‑resistant than thermoplastics but are not recyclable by melting.

相比之下，热固性塑料受热后不可逆地硬化。它们在固化过程中形成大量链间共价交联，构成刚性的三维网络。一旦固化便无法再熔化——继续加热只能导致分解。例子包括环氧树脂、硫化橡胶和三聚氰胺。热固性塑料通常比热塑性塑料更强、更耐热，但无法通过熔化回收。

9. Physical Properties and Structure | 物理性质与结构

The physical properties of polymers are determined by several structural factors: chain length (degree of polymerisation), branching, stereoregularity, and intermolecular forces. Longer chains result in greater van der Waals forces and more entanglements, raising strength and melting point.

聚合物的物理性质由多个结构因素决定：链长（聚合度）、支化度、立构规整性以及分子间作用力。链越长，范德华力越大，缠结越多，从而增加强度和熔点。

Branching affects crystallinity. Linear polymers like HDPE pack closely, giving high density, strength, and a higher melting point. Branched polymers like LDPE cannot pack together regularly, leading to lower density and flexibility. Stereoregularity – whether side groups are arranged isotactically (on the same side) or atactically (random) – also influences crystallinity. Isotactic poly(propene) is rigid and useful for moulded objects, whereas atactic poly(propene) is rubbery.

支化影响结晶度。线型聚合物如 HDPE 排列紧密，赋予其高密度、高强度和高熔点。支化聚合物如 LDPE 无法规整堆砌，因此密度较低且更柔韧。立构规整性——侧基是全同（同侧）还是无规（随机）排列——也影响结晶度。全同聚丙烯刚性大，适用于模塑制品，而无规聚丙烯则呈橡胶态。

Intermolecular forces are crucial. Polyamides and polyesters have permanent dipole–dipole interactions and hydrogen bonds, making them stronger and more heat‑resistant than non‑polar polyalkenes. PTFE, despite its weak dispersion forces, has a very high melting point because of the stiffness of the C–F bonds and the linear packing.

分子间作用力至关重要。聚酰胺和聚酯具有永久偶极‑偶极相互作用和氢键，比非极性的聚烯烃更强、更耐热。PTFE 虽然只有弱的色散力，但由于 C–F 键刚性大且线型排列，熔点非常高。

10. Biodegradability and Environmental Impact | 生物可降解性与环境影响

Most addition polymers derived from alkenes have a backbone of only carbon–carbon single bonds, which are very resistant to chemical attack. They are not broken down by microorganisms and can persist in the environment for hundreds of years. This causes significant waste pollution, especially in oceans.

大多数由烯烃制得的加成聚合物主链仅由碳碳单键构成，极难发生化学降解。它们不能被微生物分解，可在环境中存续数百年。这导致了严重的废弃物污染，尤其在海洋中。

Condensation polymers, especially polyesters, are more susceptible to hydrolysis because of the polar ester linkages. Under microbial action, water can break down the ester bonds into smaller, digestible fragments. Biodegradable plastics such as poly(lactic acid) (PLA) derived from renewable starch or sugar are designed to be compostable.

缩合聚合物，特别是聚酯，由于含有极性的酯键，更易水解。在微生物作用下，水可断裂酯键，形成更小的、可被消化的小分子。可生物降解塑料，如由可再生淀粉或糖制得的聚乳酸 (PLA)，被设计为可堆肥。

Photodegradable plastics contain additives that absorb UV light and cause chain scission. Oxidation can also break polyalkenes if pro‑oxidant additives are included. However, bio‑based does not always mean biodegradable; bio‑PET is chemically identical to fossil‑fuel PET and is not naturally degradable. Edexcel questions may ask you to discuss the advantages and disadvantages of biodegradable polymers versus traditional plastics.

光降解塑料含有吸收紫外光并引发断链的添加剂。若添加助氧化剂，也可使聚烯烃氧化断裂。但“生物基”并不总意味着可生物降解；生物基 PET 在化学上与化石燃料 PET 完全相同，并非天然可降解。Edexcel 考题可能会要求讨论可生物降解聚合物与传统塑料相比的优缺点。

11. Recycling and Life‑cycle Analysis | 回收与生命周期分析

There are three main approaches to managing polymer waste: mechanical recycling, chemical recycling, and incineration with energy recovery. Mechanical recycling involves sorting, washing, melting, and re‑forming thermoplastics. However, each cycle can reduce chain length (down‑cycling), and contamination limits the quality of the recycled material.

处理聚合物废弃物主要有三种途径：机械回收、化学回收以及焚烧发电。机械回收包括分类、清洗、熔化并重新成型热塑性塑料。但每次循环都可能降低链长（降级回收），而且污染会限制再生料的质量。

Chemical recycling breaks the polymer back into its monomers or short oligomers, which can then be repolymerised into virgin‑quality plastic. For example, PET can be hydrolysed to terephthalic acid and ethane‑1,2‑diol. This is more energy‑intensive but offers true circularity. Feedstock recycling converts mixed plastics into synthesis gas or liquid fuels via pyrolysis.

化学回收将聚合物分解回单体或短低聚物，然后可重新聚合成原始品质的塑料。例如，PET 可水解为对苯二甲酸和乙二醇。该方法能耗更高，但可真正实现循环利用。原料回收则通过热解将混合塑料转化为合成气或液体燃料。

A life‑cycle analysis (LCA) considers the environmental impact from raw material extraction, through production and use, to disposal. Plastics made from renewable resources may have a lower carbon footprint, but their end‑of‑life fate remains critical. Edexcel often sets LCA comparison questions between, say, a plastic carrier bag and a paper bag. Factors include energy input, water usage, biodegradability, and release of pollutants.

生命周期分析 (LCA) 考虑从原料提取、生产、使用到处置的全过程环境影响。由可再生资源制成的塑料可能碳足迹较低，但其最终处置依然至关重要。Edexcel 常出题让比较塑料包装袋与纸袋的 LCA，考量因素包括能源投入、水耗、可生物降解性及污染物排放。

12. Summary and Exam Tips | 总结与考试技巧

Polymer chemistry is a topic where structured recall and clear diagrams earn marks efficiently. Always label repeat units correctly – use square brackets, the extending bonds, and the subscript ‘n’. When deducing a monomer from a condensation polymer, identify the linkage (ester or amide), mentally add water across it, and reconstruct the monomer(s).

聚合物化学是一个通过结构化记忆和清晰示意图即可高效得分的话题。务必正确标注重复单元——使用方括号、延长键和下标 n。从缩合聚合物反推单体时，先识别键接类型（酯或酰胺），在心中加水断键，重建出单体（或两种单体）。

Understand the distinction between addition and condensation in terms of both mechanism and environmental fate. Addition polymers are typically non‑biodegradable; condensation polymers with ester or amide links can hydrolyse. In problems involving molar mass, use the degree of polymerisation and the mass of the repeat unit. For instance, the average molar mass of poly(ethene) = n × 28 g mol⁻¹, where n is the number of ethene units.

要理解加成与缩合在机理和环境归宿方面的区别。加成聚合物通常不可生物降解；带有酯键或酰胺键的缩合聚合物可水解。在涉及摩尔质量的问题中，使用聚合度和重复单元的质量进行计算。例如，聚乙烯的平均摩尔质量 = n × 28 g mol⁻¹，其中 n 为乙烯单元数。

Finally, practise drawing repeat units for PET, nylon‑6,6, and a few common addition polymers. Pay attention to the exact position of the functional groups and the loss of the small molecule. With this foundation, polymer questions become a reliable source of marks on the IB and Edexcel chemistry papers.

最后，多加练习 PET、尼龙‑6,6 和几种常见加成聚合物重复单元的绘制。注意官能团的确切位置和小分子的脱去。有了这些基础，聚合物题目将成为 IB 和 Edexcel 化学试卷中可靠的得分来源。

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Polymer Chemistry: Key Concepts for IB Edexcel | IB Edexcel 化学：聚合物 考点精讲