📚 GCSE Edexcel Chemistry: Polymers Key Points | GCSE 爱德思化学：聚合物考点精讲
Polymers are giant covalent or long-chain molecules built from many small repeating units called monomers. In GCSE Edexcel Chemistry, you need to understand both addition and condensation polymerisation, be able to deduce the monomer from a polymer section and vice versa, and relate polymer properties to their uses. You must also know the structures of important natural condensation polymers such as proteins, starch, and DNA. This revision guide covers every key point you need for the exam, with clear comparisons and worked examples.
聚合物是由许多称为单体的小重复单元构成的大分子或长链分子。在 GCSE 爱德思化学中，你需要掌握加成聚合与缩合聚合、从聚合物链段推断单体（或反之），以及将聚合物的性质与其用途联系起来。你还必须了解重要的天然缩合聚合物（如蛋白质、淀粉和 DNA）的结构。本复习指南涵盖考试所需的每个关键点，并提供清晰的对比和例题讲解。
1. What Are Polymers? | 什么是聚合物？
Polymers are macromolecules formed by the covalent linking of many small molecules called monomers. The process is called polymerisation. There are two main types: addition polymerisation and condensation polymerisation. Addition polymers are made from alkenes; condensation polymers are made from monomers with two functional groups, often producing a small molecule such as water or hydrogen chloride as a by‑product.
聚合物是由许多称为单体的小分子通过共价键连接而成的大分子。这一过程称为聚合。主要分为两种类型：加成聚合和缩合聚合。加成聚合物由烯烃制得；缩合聚合物由带有两个官能团的单体制得，通常会生成水或氯化氢等小分子副产物。
- Monomer: a small molecule that can join with many others to form a polymer.
- 单体的定义: 能够与许多同类分子连接形成聚合物的小分子。
- Polymer: a long molecule made of many repeating units; the repeating unit has the same atoms as the monomer (in addition) or slightly fewer atoms (in condensation).
- 聚合物的定义: 由大量重复单元组成的长链分子；重复单元的原子组成在加成聚合中与单体相同，在缩合聚合中略少（因失去小分子）。
2. Addition Polymerisation | 加成聚合
pens up and monomers join end to end without the loss of any atoms. The polymer contains only single bonds in the backbone. Common examples include poly(ethene), poly(propene), and poly(chloroethene) (PVC). To draw the polymer, show the repeat unit in brackets with extending bonds, and place an 'n' outside to indicate many repeats.
加成聚合涉及烯烃单体。C=C 双键打开，单体首尾相连，没有原子丢失。聚合物主链中只含有单键。常见例子有聚（乙烯）、聚（丙烯）和聚（氯乙烯）（PVC）。画聚合物时，将重复单元放在方括号内，两端用延伸键表示，并在括号外标注“n”来表示大量重复。
Monomer: CH₂=CH₂ → Polymer: –[CH₂–CH₂]ₙ–
单体: CH₂=CH₂ → 聚合物: –[CH₂–CH₂]ₙ–
- The empirical formula of the repeat unit is the same as that of the monomer.
- 重复单元的经验式与单体的经验式相同。
- Poly(ethene) is used for plastic bags and bottles; poly(propene) for ropes and crates; PVC for window frames and pipes.
- 聚（乙烯）用于塑料袋和瓶子；聚（丙烯）用于绳索和板条箱；聚氯乙烯用于窗框和管道。
3. Deducing Monomers from Addition Polymers | 从加成聚合物推断单体
single bond. Replace that single bond with a C=C double bond to obtain the original alkene monomer. If there are side groups such as –Cl or –CH₃, attach them to one of the carbons as in the monomer.
从加成聚合物倒推单体时，先识别括号内的重复单元。重复单元通常由两个碳原子以单键连接。将该单键替换为 C=C 双键，即可得到原来的烯烃单体。如果有 –Cl 或 –CH₃ 等侧基，则把它们连在其中一个碳上，与单体结构一致。
Polymer repeat: –[CH₂–CHCl]ₙ– → Monomer: CH₂=CHCl
聚合物重复单元: –[CH₂–CHCl]ₙ– → 单体: CH₂=CHCl
Always check that the monomer has a double bond and the correct number of hydrogen atoms. This is a common exam question — make sure you can draw both the displayed and structural formulae.
务必检查单体含有一个双键且氢原子个数正确。这是常见的考试题型——确保你能画出展示式和结构式。
4. Condensation Polymerisation | 缩合聚合
Condensation polymerisation involves monomers with two functional groups. Each time two monomers join, a small molecule (usually water or HCl) is lost. Common types of condensation polymers are polyesters and polyamides. A polyester is made from a diol (two –OH groups) and a dicarboxylic acid (two –COOH groups). A polyamide is made from a diamine (two –NH₂ groups) and a dicarboxylic acid, or from amino acids. Every ester or amide link formed releases one water molecule.
缩合聚合涉及带有两个官能团的单体。每两个单体连接时，会失去一个小分子（通常是水或 HCl）。常见的缩合聚合物有聚酯和聚酰胺。聚酯由二醇（两个 –OH）与二羧酸（两个 –COOH）制成。聚酰胺由二胺（两个 –NH₂）与二羧酸，或由氨基酸制成。每形成一个酯键或酰胺键，就释放一个水分子。
HO–R–OH + HOOC–R'–COOH → –[O–R–OOC–R'–CO]ₙ– + n H₂O
二醇 + 二酸 → 聚酯 + 水
- Polyester example: terylene (PET) from ethane‑1,2‑diol and benzene‑1,4‑dicarboxylic acid.
- 聚酯例子：涤纶（PET）由乙烷-1,2-二醇与对苯二甲酸制得。
- Polyamide example: nylon‑6,6 from 1,6‑diaminohexane and hexanedioic acid.
- 聚酰胺例子：尼龙-6,6 由 1,6-二氨基己烷与己二酸制得。
5. Deducing Monomers from Condensation Polymers | 从缩合聚合物推断单体
For a polyester, break the ester links (–COO–) by adding water: the –CO– part becomes –COOH, and the –O– part becomes –OH. Thus you obtain a diol and a dicarboxylic acid. For a polyamide, break the amide links (–CONH–) with water: the –CO– part becomes –COOH, and the –NH– part becomes –NH₂, giving a diamine and a diacid (or an amino acid if the chain comes from a single monomer).
对于聚酯，拆开酯键（–COO–）并加水：–CO– 部分变成 –COOH，–O– 部分变成 –OH，从而得到二醇和二羧酸。对于聚酰胺，拆开酰胺键（–CONH–）并加水：–CO– 部分变成 –COOH，–NH– 部分变成 –NH₂，得到二胺和二酸（若主链由单一单体形成，则得到氨基酸）。
–[OC–R–COO–R'–O]ₙ– + 2n H₂O → n HOOC–R–COOH + n HO–R'–OH
聚酯水解：得二酸与二醇
You will not be asked to write full hydrolysis equations, but you should be able to identify the two monomer units clearly and draw their structures. Always show the functional groups at both ends.
考试不会要求写出完整的水解方程式，但你应能清楚地识别两种单体单元并画出结构。务必在两端标出官能团。
6. Natural Polymers – Proteins | 天然聚合物——蛋白质
Proteins are natural condensation polymers made from amino acid monomers. An amino acid has both an amine group (–NH₂) and a carboxyl group (–COOH). When amino acids join, they form amide (peptide) links, releasing water. A chain of amino acids is a polypeptide; proteins are long polypeptides folded into specific shapes. The sequence and shape determine the protein's function, e.g. enzymes, haemoglobin, antibodies.
蛋白质是由氨基酸单体构成的天然缩合聚合物。氨基酸同时含有胺基（–NH₂）和羧基（–COOH）。氨基酸连接时形成酰胺（肽）键并释放水。氨基酸链称为多肽；蛋白质是由多肽折叠成特定形状的长链。序列和形状决定了蛋白质的功能，如酶、血红蛋白、抗体等。
Glycine + Glycine → Gly‑Gly dipeptide + H₂O
甘氨酸 + 甘氨酸 → 甘氨酰甘氨酸二肽 + 水
- Peptide link: –CONH– (amide group).
- 肽键：–CONH–（酰胺基团）。
- Protein molecules are held in shape by hydrogen bonds and other interactions; heat or pH change can denature the protein, breaking these bonds.
- 蛋白质分子由氢键和其他作用力维持形状；加热或酸碱变化可使蛋白质变性，破坏这些键。
7. Natural Polymers – Carbohydrates | 天然聚合物——碳水化合物
Starch and cellulose are natural condensation polymers made from glucose monomers. Glucose molecules join by glycosidic bonds, eliminating water. Starch is a mixture of two polymers: amylose (straight chain, mainly α‑1,4 links) and amylopectin (branched, α‑1,4 and α‑1,6 links). Cellulose has β‑glucose units linked by β‑1,4 bonds, forming strong straight fibres that make plant cell walls rigid.
淀粉和纤维素是由葡萄糖单体构成的天然缩合聚合物。葡萄糖分子通过糖苷键连接，脱去水。淀粉是两种聚合物的混合物：直链淀粉（直链，主要是 α-1,4 键）和支链淀粉（分支，含 α-1,4 和 α-1,6 键）。纤维素由 β-葡萄糖以 β-1,4 键连接，形成坚固的直链纤维，使植物细胞壁坚硬。
n C₆H₁₂O₆ → (C₆H₁₀O₅)ₙ + n H₂O
n 个葡萄糖 → 多糖 + n 个水
Both are huge molecules; starch is used for energy storage in plants, cellulose for structural support. In the exam, you may need to explain why starch can be digested by humans but cellulose cannot (due to different glycosidic bond orientation).
两者都是大分子；淀粉用于植物储能，纤维素用于结构支撑。考试中可能需要解释为何人体能消化淀粉而无法消化纤维素（因糖苷键取向不同）。
8. DNA as a Condensation Polymer | 作为缩合聚合物的 DNA
DNA (deoxyribonucleic acid) is a natural condensation polymer. Each strand has a sugar‑phosphate backbone, with organic bases attached. The monomer is a nucleotide, consisting of a phosphate group, a deoxyribose sugar, and a nitrogenous base (A, T, C, G). Nucleotides join by condensation reactions between the phosphate of one and the sugar of the next, forming strong phosphodiester links. Two strands wind into a double helix, held by hydrogen bonds between complementary base pairs (A‑T, C‑G).
DNA（脱氧核糖核酸）是一种天然缩合聚合物。每条链都有糖-磷酸骨架，并连接有机碱基。单体是核苷酸，由磷酸基团、脱氧核糖和含氮碱基（A、T、C、G）组成。核苷酸通过一个核苷酸的磷酸与下一个核苷酸的糖之间发生缩合反应连接，形成牢固的磷酸二酯键。两条链盘绕成双螺旋，由互补碱基对（A-T、C-G）之间的氢键维持。
When asked to compare DNA and synthetic polymers, note that both have repeating units and form by condensation. DNA carries genetic information because of the specific sequence of bases.
当要求比较 DNA 与合成聚合物时，注意两者都有重复单元，且均通过缩合形成。DNA 能携带遗传信息是因为碱基的特定序列。
9. Thermoplastics vs. Thermosets | 热塑性塑料与热固性塑料
Addition polymers are usually thermoplastics — they soften when heated and harden when cooled, and can be remoulded. This is because there are only weak intermolecular forces between chains, no cross‑links. Examples: poly(ethene), PVC. Condensation polymers can be thermoplastics (like some nylons) or thermosets if heavily cross‑linked (like melamine). Thermosets char or decompose on strong heating and cannot be remelted because covalent cross‑links lock the chains.
加成聚合物通常是热塑性塑料——加热变软，冷却变硬，可反复重塑。这是因为链间只有弱的分子间作用力，没有交联。例如：聚乙烯、PVC。缩合聚合物若存在大量交联，则可能是热固性塑料（如三聚氰胺）。热固性塑料强热下会炭化或分解，无法再熔化，因为共价交联将链锁住。
| Property | Thermoplastic | Thermoset |
|---|---|---|
| 响应加热 | Softens, melts | Does not melt, usually chars |
| 链间力 | Weak intermolecular forces | Strong covalent cross‑links |
| 可回收性 | Can be remoulded, recyclable | Cannot be remelted, difficult to recycle |
10. Properties and Uses of Common Polymers | 常见聚合物的性质与用途
The properties of a polymer depend on its structure: chain length, branching, presence of cross‑links, and intermolecular forces. Crystalline regions (chains packed closely) make polymers stiffer and stronger; amorphous regions make them more flexible. Modifying the monomer or adding plasticisers can alter these properties.
聚合物的性质取决于其结构：链长、支化程度、交联情况以及分子间作用力。结晶区（链排列紧密）使聚合物更硬更强；无定形区使其更具柔韧性。改变单体或添加增塑剂可以调整这些性质。
- Poly(ethene) – low density (LDPE): branched chains, flexible, used for carrier bags. High density (HDPE): straighter chains, stronger, used for bottles.
- 聚乙烯 – 低密度（LDPE）：支链多，柔软，用于购物袋。高密度（HDPE）：链较直，强度大，用于瓶子。
- Poly(propene) – tough, resistant to chemicals, used for medical syringes and food containers.
- 聚丙烯 – 坚韧、耐化学品，用于医用注射器和食品容器。
- PVC – rigid with strong dipole‑dipole forces (due to C–Cl bond), used for pipes; adding plasticisers makes it flexible for imitation leather.
- 聚氯乙烯 – 刚性，因 C–Cl 键产生强偶极-偶极力，用于管道；加入增塑剂后可变得柔软，制成人造革。
- Nylon – strong, elastic, used for ropes, fabrics, and toothbrush bristles.
- 尼龙 – 强度高、有弹性，用于绳索、织物和牙刷刷毛。
- Polyesters (PET) – crease‑resistant, used for clothing and drink bottles.
- 聚酯（PET）– 防皱，用于服装和饮料瓶。
11. Environmental Issues with Polymers | 聚合物引发的环境问题
Most synthetic polymers are non‑biodegradable because microorganisms lack enzymes to break down the strong C–C and C–H bonds. This leads to litter, harm to wildlife, and microplastic pollution. Incineration produces CO₂ and possibly toxic gases (e.g. HCl from PVC). Recycling conserves resources and reduces landfill, but separation of different polymers is difficult and costly. Biodegradable polymers made from starch or plant oils can be broken down by microbes, but they are more expensive and sometimes less durable.
大多数合成聚合物不可生物降解，因为微生物缺少能打断强 C–C 和 C–H 键的酶。这会导致垃圾污染、危害野生动物及微塑料污染。焚烧会产生 CO₂ 和可能有毒气体（如 PVC 产生的 HCl）。回收利用可节约资源、减少填埋，但分离不同种类的聚合物困难且成本高昂。由淀粉或植物油制成的可生物降解聚合物能被微生物分解，但价格较高且有时耐用性较差。
- Reduce, reuse, recycle: the 3Rs approach.
- 3R 原则：减少使用、重复使用、循环回收。
- Feedstock recycling: breaking polymers back into monomers for re‑polymerisation.
- 原料回收：将聚合物分解回单体，再用于聚合。
- In the exam, you may be asked to evaluate the life cycle of a polymer product, considering raw materials, manufacture, use, and disposal.
- 考试中可能要求评估聚合物产品的生命周期，考虑原料、制造、使用和处置。
12. Exam Tips and Common Mistakes | 应试技巧与常见错误
ing an addition polymer repeat unit, always show the bonds extending through the brackets: –[CH₂–CH₂]ₙ–. Do not write CH₂=CH₂ inside the brackets. The 'n' must be outside the brackets.
画加成聚合物重复单元时，务必显示键穿过括号：–[CH₂–CH₂]ₙ–。不要在括号内写 CH₂=CH₂。“n”必须放在括号外。
2. For a condensation polymer, clearly show the ester or amide links in the repeat unit. If asked to draw the repeating unit for PET, you must include the benzene ring correctly. Common mistake: forgetting to balance the number of carbons or missing functional groups.
对于缩合聚合物，要在重复单元中清楚地显示酯键或酰胺键。若要求画 PET 的重复单元，必须正确画出苯环。常见错误：碳原子数不平衡或遗漏官能团。
3. Comparing proteins, starch, and DNA: all are condensation polymers. Know the monomer for each: amino acids for proteins, glucose for starch, nucleotides for DNA. Know the type of link: peptide, glycosidic, phosphodiester.
比较蛋白质、淀粉和 DNA：三者都是缩合聚合物。掌握各自单体和键型：蛋白质单体是氨基酸，键为肽键；淀粉单体是葡萄糖，键为糖苷键；DNA 单体是核苷酸，键为磷酸二酯键。
4. Use precise language: 'addition polymerisation requires a C=C double bond', 'condensation polymerisation releases a small molecule', 'thermosets have covalent cross‑links', etc.
使用严谨的语言：“加成聚合需要 C=C 双键”“缩合聚合释放小分子”“热固性塑料有共价交联”等。
5. Practice deducing monomers in both directions. Check that the total atoms in the monomers equal the repeat unit plus the small molecule(s) lost.
练习正反向推断单体。检查单体的总原子数是否等于重复单元加上失去的小分子。
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