📚 Polymers in IB AQA Chemistry: Key Concepts | IB AQA 化学：聚合物 考点精讲
Polymers are large molecules formed by the covalent bonding of many smaller units called monomers. In IB and AQA Chemistry, you are expected to understand addition and condensation polymerisation, recognise repeating units, and explain how polymer properties relate to structure. This article provides a bilingual, topic-focused revision guide covering every key concept you need for the exam.
聚合物是由许多称为单体的小单元通过共价键连接而成的大分子。在 IB 和 AQA 化学考试中，你需要理解加成聚合与缩合聚合，识别重复单元，并解释聚合物的性质如何与结构相关。本文提供一份双语主题精讲，涵盖考试所需的每个关键概念。
1. What Are Polymers? | 什么是聚合物？
Polymers are macromolecules composed of repeating structural units derived from monomers. Natural polymers include proteins, starch and DNA, while synthetic polymers include polyethylene and nylon. The process of forming polymers is called polymerisation, and it can be divided into two main types: addition and condensation reactions.
聚合物是由单体衍生出的重复结构单元组成的大分子。天然聚合物包括蛋白质、淀粉和 DNA，而合成聚合物包括聚乙烯和尼龙。形成聚合物的过程称为聚合反应，主要分为两种类型：加成反应和缩合反应。
In exam questions, you must be able to identify the monomer given the polymer structure and vice versa. You should also understand the terms homopolymer (one type of monomer) and copolymer (two or more different monomers).
在考试题目中，你必须能够根据聚合物结构识别单体，反之亦然。你还应理解均聚物（一种单体）和共聚物（两种或多种不同单体）这两个术语。
2. Addition Polymerisation | 加成聚合
Addition polymerisation occurs when unsaturated monomers, typically alkenes, join together without the loss of any small molecules. The carbon–carbon double bond opens up, and the monomers link to form a long saturated carbon chain. Polyethylene, polypropylene and polystyrene are common examples.
加成聚合发生在不饱和单体（通常是烯烃）相互连接而不失去任何小分子时进行。碳-碳双键打开，单体连接形成一条长的饱和碳链。聚乙烯、聚丙烯和聚苯乙烯是常见的例子。
The reaction is initiated by free radicals, heat or a catalyst, and it proceeds by a chain mechanism. The empirical formula of the polymer is the same as that of the monomer, because no atoms are gained or lost.
该反应由自由基、加热或催化剂引发，并通过链式机理进行。聚合物的实验式与单体相同，因为没有原子获得或丢失。
n CH₂=CH₂ → –(CH₂–CH₂)–ₙ
You should be able to draw a section of the polymer chain showing at least two repeat units and label the repeating unit.
你应能画出聚合物链的一段，显示至少两个重复单元，并标出重复单元。
3. Condensation Polymerisation | 缩合聚合
Condensation polymerisation involves monomers with two functional groups that react together, eliminating a small molecule such as water or hydrogen chloride. Two main types are polyesters and polyamides. Each monomer must have at least two reactive groups, e.g. diol and dicarboxylic acid for a polyester.
缩合聚合涉及具有两个官能团的单体一起反应，消除一个小分子如水和氯化氢。主要类型有聚酯和聚酰胺。每个单体必须至少有两个反应性基团，例如二醇和二羧酸反应生成聚酯。
Unlike addition polymers, the repeating unit in a condensation polymer has a different empirical formula from the monomers because a small molecule is lost during each ester or amide bond formation.
与加成聚合物不同，缩合聚合物的重复单元与单体的实验式不同，因为每形成一个酯键或酰胺键都会失去一个小分子。
n HO–R–OH + n HOOC–R’–COOH → –(O–R–O–CO–R’–CO)–ₙ + (2n–1) H₂O
4. Monomer Types and Repeating Units | 单体类型与重复单元
For addition polymers, the monomer is the alkene itself. The repeating unit shows two carbon atoms in the backbone with substituents attached, and the double bond is absent. When drawing, use brackets and an index n; the bond through the brackets indicates continuation.
对于加成聚合物，单体就是烯烃本身。重复单元显示主链上的两个碳原子及所连接的取代基，双键消失。绘图时使用方括号和下标 n；穿过括号的键表示链的延续。
For condensation polymers such as polyesters, the repeating unit contains ester linkages (–COO–). The monomers are typically a diol and a dicarboxylic acid or a hydroxycarboxylic acid. The water molecule eliminated comes from the –OH of the acid and –H of the alcohol.
对于聚酯等缩聚物，重复单元包含酯键（–COO–）。单体通常是二醇和二羧酸，或羟基羧酸。消去的水分子来自酸的 –OH 和醇的 –H。
| Polymer Type | Monomer(s) | Linkage | Small Molecule Lost |
|---|---|---|---|
| Addition | Alkene | C–C | None |
| Polyester | Diol + dicarboxylic acid | Ester –COO– | H₂O |
| Polyamide | Diamine + dicarboxylic acid | Amide –CONH– | H₂O |
5. Polyalkenes: Structure and Properties | 聚烯烃：结构与性质
Polyalkenes such as polythene, polypropene and polyvinyl chloride are made from alkenes by addition polymerisation. They consist of long saturated carbon chains with weak van der Waals’ forces between them. The strength and melting point depend on chain length, branching and the presence of side groups.
聚烯烃，如聚乙烯、聚丙烯和聚氯乙烯，是通过烯烃加成聚合制成的。它们由长的饱和碳链组成，链间存在较弱的范德华力。其强度和熔点取决于链长、支化度以及侧基的存在。
High-density polythene (HDPE) has very little branching, allowing chains to pack closely together, giving higher density, strength and melting point. Low-density polythene (LDPE) has significant branching, preventing close packing and resulting in a more flexible, lower melting material.
高密度聚乙烯（HDPE）支链极少，分子链能够紧密堆积，因此密度、强度和熔点都更高。低密度聚乙烯（LDPE）支链较多，阻碍紧密堆积，因而更柔软、熔点更低。
Polypropene and PVC have methyl and chlorine substituents respectively, which stiffen the chain and increase intermolecular forces, explaining their diverse uses.
聚丙烯和聚氯乙烯分别带有甲基和氯取代基，增强了链的刚性并增大了分子间力，这解释了它们多样的用途。
6. Polyesters and Polyamides | 聚酯与聚酰胺
Polyesters are formed by the condensation reaction between a diol (two –OH groups) and a dicarboxylic acid (two –COOH groups). The ester linkages give the polymer some polarity, increasing intermolecular attractions compared to polyalkenes. Terylene (PET) is a common example used in clothing and bottles.
聚酯由二醇（两个 –OH 基）和二羧酸（两个 –COOH 基）的缩合反应形成。酯键赋予聚合物一定的极性，与聚烯烃相比增强了分子间的吸引力。涤纶（PET）是常见的例子，用于服装和瓶子。
Polyamides, such as nylon-6,6, are made from a diamine and a dicarboxylic acid. The repeating unit contains amide groups –CONH–. Hydrogen bonding between the N–H and C=O groups across chains gives polyamides high tensile strength and makes them suitable for fibres.
聚酰胺，如尼龙-6,6，由二胺和二羧酸制成。重复单元含有酰胺基团 –CONH–。链间 N–H 与 C=O 基团形成氢键，使聚酰胺具有高抗拉强度，适合用作纤维。
You must be able to deduce the repeat unit when provided with the formulas of the monomers, and recognise that the number of water molecules equals the number of bonds formed minus one, often simplified in equations as (2n–1) H₂O for n monomers of each type.
你必须能够根据所给单体的化学式推导出重复单元，并要认识到水分子的数目等于所形成的键的数目减一，通常在方程中简化为每种单体 n 个时生成 (2n–1) H₂O。
7. Biodegradable Polymers | 可生物降解的聚合物
Biodegradable polymers can be broken down by microorganisms into smaller, environmentally harmless molecules. These polymers often contain ester or amide groups that are susceptible to hydrolysis. Polylactic acid (PLA) from corn starch, and polyhydroxyalkanoates (PHAs) from bacteria, are important examples.
可生物降解的聚合物能被微生物分解成较小的、对环境无害的分子。这些聚合物通常含有容易被水解的酯基或酰胺基。来自玉米淀粉的聚乳酸（PLA）和来自细菌的聚羟基脂肪酸酯（PHA）是重要的例子。
The environmental advantage is that they reduce plastic waste accumulation and do not rely solely on fossil fuel feedstocks. However, their production can compete with food resources, and their degradation requires specific composting conditions.
其环境优势在于减少塑料废物堆积，且不完全依赖化石燃料原料。然而，它们的生产可能争抢食物资源，且其降解需要特定的堆肥条件。
In exams, you may be asked to explain why the presence of polar, hydrolytically cleavable bonds enables biodegradation, linking structure to function.
考试中可能要求你解释为什么极性、可水解断裂的键的存在能实现生物降解，将结构与功能联系起来。
8. Environmental Impact of Polymer Disposal | 聚合物废弃处理的环境影响
Most addition polymers are non-biodegradable because the saturated carbon–carbon backbone is chemically inert and resistant to microbial attack. Thus, they persist in landfills and as plastic pollution in oceans. Incineration can recover energy but produces CO₂ and potentially toxic gases like HCl from PVC.
大多数加成聚合物是不可生物降解的，因为饱和的碳-碳主链化学惰性，抵抗微生物的侵蚀。因此，它们会长期存在于填埋场，并成为海洋塑料污染。焚烧可以回收能量，但会产生 CO₂ 以及可能的有毒气体，如 PVC 产生的 HCl。
Recycling of thermoplastics is possible because they can be softened by heating and remoulded without chemical change. However, thermosetting polymers form covalent cross-links during curing and cannot be reshaped; they must be ground down for use as filler.
热塑性塑料可以回收，因为它们可以加热软化并可重新成型而不发生化学变化。而热固性聚合物在固化过程中形成了共价交联，无法重塑；它们必须被粉碎用作填充材料。
Biodegradable and compostable polymers offer an alternative, but proper collection and industrial composting infrastructure are essential to realise their benefits. Exam questions may ask you to evaluate different disposal methods with regard to sustainability.
可生物降解和可堆肥聚合物提供了一种替代方案，但必须要有妥善的收集和工业堆肥基础设施才能发挥其优势。考试题目可能要求你从可持续性角度评估不同的废弃处理方式。
9. Drawing and Interpreting Repeat Units | 绘制和解读重复单元
A common exam task is to draw the repeat unit given the structure of a short polymer section or the monomers. For addition polymers, identify the two carbon atoms that were originally part of the double bond, and replace the double bond with single bonds extending through the brackets.
常见的考试任务是给出聚合物短链结构或单体，要求画出重复单元。对于加成聚合物，应识别出最初构成双键的两个碳原子，并将双键替换为延伸到方括号外的单键。
For condensation polymers, you must show the ester or amide functional group within the repeating unit and understand that the brackets enclose the part that repeats exactly. Remember to draw the broken bonds at each end continuing into the brackets properly.
对于缩合聚合物，必须在重复单元内显示酯基或酰胺基官能团，并明白括号内的部分是完全重复的部分。记住要正确绘制每端伸入方括号的断键。
Practise drawing polyethene, polypropene, polyvinyl chloride, PET and nylon-6,6 repeat units. Be careful with the number of carbon atoms and the correct placement of side groups.
练习绘制聚乙烯、聚丙烯、聚氯乙烯、PET 和尼龙-6,6 的重复单元。注意碳原子数目和侧基的正确位置。
10. Typical Exam Questions and Answers | 典型考试问答
Question: Polypropene is formed from propene. Draw the repeating unit of polypropene and explain why it is an addition polymer.
问题：聚丙烯由丙烯形成。画出聚丙烯的重复单元，并解释为什么它是加成聚合物。
Answer: The repeating unit is –(CH(CH₃)–CH₂)–. It is an addition polymer because no small molecules are eliminated; the double bond opens up and monomers simply add to each other.
答案：重复单元为 –(CH(CH₃)–CH₂)–。它是加成聚合物，因为没有小分子被消去；双键打开，单体彼此简单加成。
Question: Compare the biodegradability of polyethylene and polylactic acid, relating your answer to their chemical structures.
问题：比较聚乙烯和聚乳酸的生物可降解性，关联它们的化学结构进行回答。
Answer: Polyethylene has a non-polar, saturated hydrocarbon backbone that is resistant to hydrolysis and microbial breakdown. Polylactic acid contains ester linkages that are polar and can be hydrolysed to lactic acid, which microorganisms can then utilise, making it biodegradable.
答案：聚乙烯具有非极性的饱和烃骨架，对水解和微生物分解均有抗性。聚乳酸含有酯键，该键具有极性且可被水解为乳酸，微生物能够利用乳酸，因此聚乳酸可生物降解。
Practice with similar questions, ensuring you can move fluently between monomers, polymers and repeating units.
通过类似的题目进行练习，确保你能在单体、聚合物和重复单元之间自如转换。
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