📚 Synthetic Polymers | 合成聚合物
In Edexcel IGCSE Science (Chemistry), Topic 4.8 explores the fascinating world of synthetic polymers — long-chain molecules made by linking small monomer units. Understanding how addition and condensation polymers form, how their structures determine properties, and the environmental challenges they pose is essential for success in your exams and for appreciating the materials that shape modern life.
在 Edexcel IGCSE 科学（化学）中，主题 4.8 探索了合成聚合物的迷人世界——由小单体单元连接而成的长链分子。理解加成聚合和缩合聚合如何形成、它们的结构如何决定性质，以及它们带来的环境挑战，对于你通过考试和认识塑造现代生活的材料都至关重要。
1. What Are Polymers? | 什么是聚合物？
A polymer is a large molecule built from many smaller, repeating units called monomers. The process of joining monomers together is polymerisation. Polymers can be natural, such as proteins, starch and DNA, or synthetic, like plastics and nylon. In this topic, we focus mainly on synthetic polymers and their production from organic monomers derived from crude oil.
聚合物是由许多较小的重复单元（称为单体）构建而成的大分子。将单体连接在一起的过程叫做聚合。聚合物可以是天然的，如蛋白质、淀粉和 DNA，也可以是合成的，如塑料和尼龙。在本主题中，我们主要关注合成聚合物以及它们从原油中提炼出的有机单体的生产。
2. Addition Polymerisation | 加成聚合
Addition polymerisation occurs when unsaturated monomers containing a carbon– er. The double bond breaks open, allowing monomers to bond covalently to each other, forming a long chain. No other product is formed — ion polymerisation. Ethene (C₂H₄) is the simplest monomer, and its polymer is poly(ethene), commonly known as polythene.
加成聚合发生在含有碳碳双键（C=C）的不饱和单体连接在一起时。双键打开，使单体彼此共价键合，形成长链。没有其他产物生成——这是加成聚合的一个关键特征。乙烯（C₂H₄）是最简单的单体，其聚合物是聚乙烯，通常称为聚乙烯塑料。
3. Drawing Addition Polymers | 绘制加成聚合物
To draw the repeat unit of an addition polymer, break the double bond in the monomer and replace it with a single bond, then extend the bond through brackets and show 'n' for many repeats. For poly(ethene), the repeat unit is –CH₂–CH₂–. For poly(propene) (from C₃H₆), the repeat unit includes a CH₃ side group: –CH₂–CH(CH₃)–. You must be able to draw the monomer given the polymer, and vice versa.
要绘制加成聚合物的重复单元，先断开单体中的双键并以单键代替，然后将键延伸到括号内并标注“n”表示多个重复。对于聚乙烯，重复单元为 –CH₂–CH₂–。对于聚丙烯（由 C₃H₆ 制成），重复单元含有 CH₃ 侧基：–CH₂–CH(CH₃)–。你必须能够根据聚合物绘制单体，反之亦然。
4. Common Addition Polymers | 常见的加成聚合物
Several addition polymers are vital in everyday life. Poly(ethene) is used for plastic bags and bottles; poly(propene) for ropes and carpets; poly(chloroethene) (PVC) for window frames and pipes; and poly(tetrafluoroethene) (PTFE) for non-stick coatings. Each polymer's properties are linked to the type of monomer and the arrangement of side groups along the chain.
几种加成聚合物在日常生活中至关重要。聚乙烯用于塑料袋和瓶子；聚丙烯用于绳子和地毯；聚氯乙烯（PVC）用于窗框和管道；聚四氟乙烯（PTFE）用于不粘涂层。每种聚合物的性质与单体类型以及链上侧基的排列方式密切相关。
5. Condensation Polymerisation | 缩合聚合
Condensation polymerisation involves monomers with two reactive functional groups. When these monomers react, they form a polymer and release a small molecule, usually water (H₂O) or hydrogen chloride (HCl). This is in contrast to addition polymerisation where no small molecule is lost. Common condensation polymers include polyesters and polyamides (nylons).
缩合聚合涉及带有两个反应性官能团的单体。这些单体反应时，生成聚合物的同时会释放一个小分子，通常是水（H₂O）或氯化氢（HCl）。这与加成聚合不同，后者没有小分子丢失。常见的缩合聚合物包括聚酯和聚酰胺（尼龙）。
6. Polyesters – An Example of Condensation Polymers | 聚酯——缩合聚合物的例子
A polyester forms when a dicarboxylic acid (with two –COOH groups) reacts with a diol (with two –OH groups). Each ester linkage (–COO–) connects the monomers, and water is eliminated. The simplest polyester, Terylene, is made from ethane-1,2-diol and benzene-1,4-dicarboxylic acid. You should be able to identify the ester group in the repeat unit and draw the monomers from a given section of a polyester chain.
聚酯是由二羧酸（含两个 –COOH 基团）与二醇（含两个 –OH 基团）反应生成的。每个酯键（–COO–）连接单体，同时脱去水。最简单的聚酯涤纶是由乙二醇和对苯二甲酸制成的。你应该能够识别重复单元中的酯基，并从给定的聚酯链段画出单体。
7. DNA – A Natural Condensation Polymer | DNA——天然缩合聚合物
DNA (deoxyribonucleic acid) is a natural polymer built from nucleotide monomers. Each nucleotide consists of a sugar, a phosphate group and a nitrogenous base. Condensation polymerisation links nucleotides together via sugar–phosphate backbones, forming the famous double helix structure. Understanding DNA as a polymer highlights the importance of condensation reactions in biology.
DNA（脱氧核糖核酸）是一种由核苷酸单体构成的天然聚合物。每个核苷酸包含一个糖、一个磷酸基和一个含氮碱基。缩合聚合通过糖–磷酸骨架将核苷酸连接，形成著名的双螺旋结构。将 DNA 理解为一种聚合物，突显了缩合反应在生物学中的重要性。
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, such as poly(ethene) and PVC, soften when heated and harden upon cooling; this process is reversible because the polymer chains are held by weak intermolecular forces. Thermosetting polymers, like Bakelite, do not soften on reheating because they have strong covalent cross-links between chains, forming a rigid, heat-resistant network.
聚合物可根据对热的反应分类。热塑性塑料，如聚乙烯和 PVC，加热时变软，冷却后硬化；此过程可逆，因为聚合物链由弱分子间作用力维系。热固性聚合物，如电木，重新加热时不会变软，因为链间有强共价交联，形成刚硬耐热的网络结构。
9. Structure Determines Properties | 结构决定性质
The properties of a polymer depend on chain length, branching and cross-linking. Short, branched chains produce flexible, low-density polymers (LDPE), while long, linear chains create stronger, high-density polymers (HDPE). The presence of polar groups (like Cl in PVC) makes a polymer stiffer and more resistant to chemicals. These structure–property relationships guide the design of materials for specific uses.
聚合物的性质取决于链长、支化和交联。短而带支链的链产生柔韧的低密度聚合物（LDPE），而长而无支链的链产生更强的高密度聚合物（HDPE）。极性基团（如 PVC 中的 Cl）使聚合物更硬且更耐化学腐蚀。这些结构–性质关系指导着特定用途材料的设计。
10. Disposal and Environmental Impact | 处理与环境影响
Most synthetic polymers are non-biodegradable, leading to persistent waste and pollution. Landfill sites accumulate plastics, while incineration can release toxic gases. Recycling is a key strategy: thermoplastics can be melted and remoulded. However, sorting different polymer types and contamination remain challenges. Some modern polymers, such as polylactic acid (PLA), are designed to be biodegradable or compostable.
大多数合成聚合物不可生物降解，导致持久性废物和污染。垃圾填埋场堆积塑料，焚烧会释放有毒气体。回收是重要策略：热塑性塑料可熔化重铸。然而，分类不同聚合物类型和污染仍是挑战。一些现代聚合物，如聚乳酸（PLA），被设计为可生物降解或可堆肥。
11. Biodegradable and Bioplastics | 生物降解塑料与生物塑料
Biodegradable polymers can be broken down by microorganisms into water, carbon dioxide and biomass. Polyesters made from lactic acid or starch-based polymers degrade under compost conditions. These materials reduce reliance on crude oil and lessen the environmental footprint. However, they require specific disposal facilities and do not degrade quickly in all environments.
生物降解聚合物可以被微生物分解为水、二氧化碳和生物质。由乳酸制成的聚酯或淀粉基聚合物在堆肥条件下可降解。这些材料减少了对原油的依赖，减轻了环境足迹。然而，它们需要特定的处理设施，且并非在所有环境下都能迅速降解。
12. Key Exam Tips for Polymers | 聚合物考试要点
In the exam, be prepared to draw repeat units accurately — use brackets and the 'n'. Count the atoms in the monomer and in the repeat unit to ensure they match. For condensation polymers, identify the small molecule eliminated and highlight the ester or amide linkage. Use the correct vocabulary: thermoplastic, thermoset, addition, condensation, biodegradable. Always link structure to a specific property when answering extended questions.
在考试中，要做好精确绘制重复单元的准备——使用括号和“n”。数清单体和重复单元中的原子以确保它们匹配。对于缩合聚合物，要识别消除的小分子并突出酯键或酰胺键。使用正确的词汇：热塑性塑料、热固性塑料、加成、缩合、可生物降解。在回答扩展问题时，始终将结构与特定性质联系起来。
Published by TutorHao | Chemistry Revision Series | aleveler.com
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