📚 Polymers: IGCSE AQA Chemistry Exam Focus | IGCSE AQA 化学：聚合物 考点精讲
Polymers are everywhere, from the plastics in your phone case to the proteins in your body. In IGCSE AQA Chemistry, polymers is a topic that bridges organic chemistry, materials science, and biology. Understanding addition and condensation polymerisation, as well as the structure and function of natural polymers, is essential for success in the exam. This article breaks down every key concept you need, complete with clear examples and typical exam tips.
聚合物无处不在，从手机壳的塑料到你体内的蛋白质。在 IGCSE AQA 化学中，聚合物是连接有机化学、材料科学与生物学的桥梁。掌握加成聚合与缩合聚合，以及天然聚合物的结构与功能，是考试成功的关键。本文将逐一解析你需要掌握的每个核心概念，并提供清晰的示例和典型应试技巧。
1. What are Polymers? | 什么是聚合物？
A polymer is a very large molecule (macromolecule) built from many small, repeating units called monomers. The word ‘polymer’ comes from Greek: ‘poly’ means many, ‘mer’ means part. Monomers are like building blocks – when they link together in a chain, a polymer is formed. This linking process is called polymerisation. Polymers can be synthetic, such as polythene and nylon, or natural, such as starch, cellulose, proteins and DNA.
聚合物是由许多称为单体的小重复单元构成的大分子。‘聚合物’一词源自希腊语：‘poly’表示多，‘mer’表示部分。单体就像积木——它们连接成长链时就形成了聚合物。这个连接过程叫做聚合反应。聚合物可以是合成的，如聚乙烯和尼龙，也可以是天然的，如淀粉、纤维素、蛋白质和DNA。
No matter the type, every polymer has a repeat unit – the smallest group of atoms that repeats along the chain. You need to be able to identify and draw repeat units for both addition and condensation polymers in the exam.
无论何种类型，每个聚合物都有重复单元——即沿着链重复的最小原子团。你需要能够在考试中识别并绘制加成聚合物和缩合聚合物的重复单元。
2. Addition Polymerisation | 加成聚合
Addition polymerisation occurs when alkene monomers join together without the loss of any atoms. The carbon–carbon double bond (C=C) in each monomer opens up, and the monomers add to one another to form a long saturated carbon chain. The only product is the polymer itself.
加成聚合发生时，烯烃单体连接在一起，没有任何原子丢失。每个单体中的碳碳双键 (C=C) 打开，单体相互加成，形成一条饱和的长碳链。唯一的产物就是聚合物本身。
The general equation can be written as: n monomer → polymer. For example, the polymerisation of ethene:
一般方程式可写作：n 单体 → 聚合物。例如，乙烯的聚合：
n CH₂=CH₂ → −(CH₂−CH₂)ₙ−
The repeat unit is −CH₂−CH₂−, and the polymer is named poly(ethene), often shortened to polythene. High pressure and a catalyst are typically required.
重复单元是−CH₂−CH₂−，聚合物命名为聚（乙烯），常简称为聚乙烯。通常需要高压和催化剂。
Addition polymers are always made from monomers containing a C=C bond. The polymer backbone is a continuous chain of carbon atoms, and the empirical formula of the polymer is identical to that of the monomer.
加成聚合物总是由含有C=C键的单体制成。聚合物主链是一条连续的碳原子链，聚合物的经验式与单体相同。
3. Common Addition Polymers | 常见的加成聚合物
The table below summarises four addition polymers you must know for IGCSE AQA Chemistry, along with their monomers and typical uses.
下表总结了IGCSE AQA化学必考的四种加成聚合物及其单体和典型用途。
| Monomer | Polymer | Common Uses |
|---|---|---|
| Ethene (CH₂=CH₂) | Poly(ethene) (PE) | Plastic bags, bottles, cling film |
| Propene (CH₂=CHCH₃) | Poly(propene) (PP) | Ropes, carpets, food containers |
| Chloroethene (CH₂=CHCl) | Poly(chloroethene) (PVC) | Pipes, window frames, electrical insulation |
| Phenylethene (styrene) (CH₂=CHC₆H₅) | Poly(phenylethene) (polystyrene) | Packaging, insulation, disposable cups |
中文对照：乙烯 → 聚乙烯 (PE)，用于塑料袋、瓶子、保鲜膜；丙烯 → 聚丙烯 (PP)，用于绳索、地毯、食品容器；氯乙烯 → 聚氯乙烯 (PVC)，用于管道、窗框、电线绝缘；苯乙烯 → 聚苯乙烯，用于包装、绝缘材料、一次性杯子。
Notice that the monomer names are placed in brackets after ‘poly’. In the exam, you may be asked to give the monomer for a given polymer section or vice versa.
注意单体名称放在‘聚’之后的括号中。考试可能会要求你根据给出的聚合物片段写出单体，或反之。
4. Properties and Uses of Addition Polymers | 加成聚合物的性质与用途
The physical properties of addition polymers depend on the length of the chains, the amount of branching, and the presence of cross‑links. Most addition polymers are thermoplastics – they soften when heated and can be remoulded. This is because the polymer chains are held together by weak intermolecular forces, not strong covalent cross‑links.
加成聚合物的物理性质取决于链长、支链数量和交联的存在。大多数加成聚合物是热塑性塑料——加热时软化，可以重新塑形。这是因为聚合物链之间由弱的分子间力维系，而非强的共价交联。
Low‑density poly(ethene) (LDPE) has significant branching, which prevents the chains from packing closely. This makes it flexible and suitable for carrier bags. High‑density poly(ethene) (HDPE) has less branching, so chains pack more tightly, giving it higher strength and rigidity – ideal for drainpipes and bottles.
低密度聚乙烯 (LDPE) 具有大量支链，阻止了链紧密堆积，因此柔韧，适用于购物袋。高密度聚乙烯 (HDPE) 支链较少，链堆积更紧密，具有更高的强度和刚性，是排水管和瓶子的理想选择。
Addition polymers are chemically inert and resistant to corrosion, but this also means they are non‑biodegradable. They persist in the environment for hundreds of years, creating waste disposal challenges.
加成聚合物化学惰性好且耐腐蚀，但这也意味着它们不可生物降解。它们能在环境中存留数百年，造成废物处理难题。
5. Condensation Polymerisation | 缩合聚合
Condensation polymerisation involves monomers with two functional groups reacting together and releasing a small molecule – usually water or hydrogen chloride. Unlike addition polymerisation, the monomers are not based on alkenes; instead they are often dicarboxylic acids, diols, diamines, or amino acids.
缩合聚合涉及带有两个官能团的单体反应，同时释放出小分子——通常是水或氯化氢。与加成聚合不同，单体并非基于烯烃；它们通常是二元羧酸、二元醇、二元胺或氨基酸。
For IGCSE AQA, you mainly need to know about polyesters. A polyester is formed from a dicarboxylic acid and a diol. Each time an ester linkage (−COO−) forms, a water molecule is eliminated. The polymer chain therefore contains many ester groups.
在IGCSE AQA考试中，你主要需要了解聚酯。聚酯由二元羧酸和二元醇形成。每形成一个酯键 (−COO−)，就会消除一个水分子。因此聚合物链含有许多酯基。
A general equation for polyester formation is:
聚酯形成的通式为：
n HOOC–R–COOH + n HO–R′–OH → −[OC–R–COO–R′–O]ₙ− + (2n−1) H₂O
Be careful: the repeat unit in a condensation polymer often has a different empirical formula from the starting monomers because small molecules are lost.
注意：由于小分子的丢失，缩聚物的重复单元通常与起始单体的经验式不同。
6. Polyesters: Terylene and PET | 聚酯：涤纶和PET
The most common polyester is poly(ethylene terephthalate), known as PET. It is made from benzene‑1,4‑dicarboxylic acid (terephthalic acid) and ethane‑1,2‑diol. The reaction is:
最常见的聚酯是聚对苯二甲酸乙二醇酯，简称PET。它由1,4‑苯二甲酸（对苯二甲酸）和1,2‑乙二醇制成。反应如下：
n HOOC–C₆H₄–COOH + n HO–CH₂–CH₂–OH → −[OC–C₆H₄–COO–CH₂–CH₂–O]ₙ− + (2n−1) H₂O
PET is a thermoplastic polyester used to make drinks bottles, clothing fibres (Terylene), and food trays. It can be recycled and is coded as recycling number 1. The ester linkages in polyester can be hydrolysed under certain conditions, which means polyesters are more chemically degradable than addition polymers.
PET是一种热塑性聚酯，用于制造饮料瓶、服装纤维（涤纶）和食品托盘。它可以回收，回收代码为1号。聚酯中的酯键可在一定条件下水解，这意味着聚酯比加成聚合物更容易化学降解。
In exam questions, you may be asked to draw the repeat unit of PET from its monomers or to identify the number of water molecules produced per repeat unit. Always show the ester link and the continuing bonds at each end of the repeat unit.
在考试题中，你可能会被要求根据单体制出PET的重复单元，或计算每个重复单元产生的水分子数。一定要标出酯键以及重复单元两端的续连键。
7. Natural Polymers: Proteins | 天然聚合物：蛋白质
Proteins are natural condensation polymers made from amino acid monomers. There are about 20 different naturally occurring amino acids. Each amino acid has an amine group (−NH₂) at one end and a carboxyl group (−COOH) at the other, with a variable R group. The general structure is:
蛋白质是由氨基酸单体组成的天然缩合聚合物。自然界约有20种不同的氨基酸。每个氨基酸一端有一个氨基 (−NH₂)，另一端有一个羧基 (−COOH)，并带有一个可变的R基团。通式为：
H₂N–CHR–COOH
When amino acids polymerise, the amine group of one amino acid reacts with the carboxyl group of another, forming a peptide bond (−CONH−) and releasing a water molecule. This process produces a polypeptide chain. The sequence of amino acids determines the protein’s primary structure.
当氨基酸聚合时，一个氨基酸的氨基与另一个氨基酸的羧基反应，形成肽键 (−CONH−) 并释放一个水分子。此过程生成多肽链。氨基酸的顺序决定了蛋白质的一级结构。
Repeat unit: −HN–CHR–CO−. Proteins play huge roles in living organisms: enzymes are proteins, haemoglobin carries oxygen, and keratin makes up hair and nails. The ability to fold into specific 3D shapes gives proteins their diverse functions.
重复单元：−HN–CHR–CO−。蛋白质在生物体中扮演重要角色：酶是蛋白质，血红蛋白运输氧气，角蛋白构成头发和指甲。折叠成特定三维形状的能力赋予了蛋白质多样的功能。
8. Natural Polymers: Carbohydrates | 天然聚合物：碳水化合物
Starch and cellulose are both natural polymers of glucose, a simple sugar with the formula C₆H₁₂O₆. Glucose monomers join together by condensation polymerisation – each connection forms a glycosidic bond and eliminates a water molecule.
淀粉和纤维素都是葡萄糖（分子式C₆H₁₂O₆）的天然聚合物。葡萄糖单体通过缩合聚合连接——每个连接形成一个糖苷键并消除一个水分子。
Starch is a mixture of two polysaccharides: amylose (linear α‑1,4 linked glucose) and amylopectin (branched with α‑1,6 links). Plants use starch as an energy store. Cellulose, on the other hand, consists of β‑glucose units linked by β‑1,4 glycosidic bonds. The alternating orientation of glucose units allows long, straight chains to form hydrogen bonds with neighbouring chains, creating a rigid structure ideal for plant cell walls.
淀粉是两种多糖的混合物：直链淀粉（线性α‑1,4键合葡萄糖）和支链淀粉（具有α‑1,6分支）。植物用淀粉储存能量。而纤维素由β‑葡萄糖单元通过β‑1,4糖苷键连接而成。葡萄糖单元交替排列使得长直链能与相邻链形成氢键，从而产生适合植物细胞壁的刚性结构。
Although both are made from glucose, humans can digest starch but not cellulose because the enzyme amylase only breaks α‑glycosidic bonds.
虽然两者均由葡萄糖构成，但人类能消化淀粉却不能消化纤维素，因为淀粉酶只能断裂α‑糖苷键。
9. DNA: A Natural Condensation Polymer | DNA：天然缩合聚合物
DNA (deoxyribonucleic acid) is a double‑stranded polymer. Its monomers are nucleotides, each containing a phosphate group, a deoxyribose sugar, and a nitrogenous base (adenine, thymine, cytosine or guanine). Nucleotides join via condensation reactions between the phosphate of one nucleotide and the sugar of the next, forming a sugar‑phosphate backbone with phosphodiester bonds.
DNA（脱氧核糖核酸）是一种双链聚合物。其单体是核苷酸，每个核苷酸包含一个磷酸基团、一个脱氧核糖和一个含氮碱基（腺嘌呤、胸腺嘧啶、胞嘧啶或鸟嘌呤）。核苷酸通过一个核苷酸的磷酸与下一个核苷酸的糖之间的缩合反应连接，形成带有磷酸二酯键的糖‑磷酸骨架。
The two strands are held together by hydrogen bonds between complementary base pairs (A=T, G≡C) and twist into a double helix. DNA stores genetic information, and its sequence of bases determines the order of amino acids in proteins. This makes DNA one of the most important natural polymers in biology.
两条链通过互补碱基对（A=T，G≡C）之间的氢键维系，并扭转成双螺旋结构。DNA贮存遗传信息，其碱基序列决定了蛋白质中氨基酸的顺序。这使得DNA成为生物学中最重要的天然聚合物之一。
10. Disposal and Recycling of Polymers | 聚合物的处置与回收
The widespread use of polymers has created significant waste problems. Addition polymers like polythene and PVC are non‑biodegradable; they accumulate in landfills and oceans. Burning these plastics can release toxic gases such as hydrogen chloride (from PVC) and carbon monoxide
Published by TutorHao | IGCSE Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导