📚 Polymers: A Comprehensive Revision for IB & CIE Chemistry | 聚合物：IB与CIE化学考点精讲
Polymers are giant molecules built from many small repeating units called monomers. They form the basis of both natural materials, such as DNA, proteins, and starch, and a vast range of synthetic materials including plastics, fibres, and elastomers. In IB and CIE Chemistry, you are expected to understand addition and condensation polymerisation, be able to draw repeat units from monomer structures, compare the properties of different polymer types, and evaluate environmental issues linked to polymer disposal. This revision guide covers all the essential concepts, common pitfalls, and exam techniques you need to master polymers confidently.
聚合物是由许多称为单体的小重复单元构成的大分子。它们既构成了天然材料（如DNA、蛋白质和淀粉）的基础，也构成了包括塑料、纤维和弹性体在内的大量合成材料。在IB和CIE化学考试中，你需要理解加成聚合和缩合聚合反应，能够从单体结构绘制重复单元，比较不同类型聚合物的性质，并评估与聚合物处理相关的环境问题。本复习指南涵盖了所有基本概念、常见误区和考试技巧，助你自信掌握聚合物考点。
1. What are Polymers? | 什么是聚合物？
A polymer is a long-chain molecule formed by the covalent linking of many small monomer molecules. The process is called polymerisation. Monomers typically contain a functional group or a double bond that allows them to join together. The repeat unit shows the structure of the monomer after polymerisation, enclosed in brackets with a subscript ‘n’ to indicate a large number of repeats. For example, the repeat unit of poly(ethene) is —[CH₂—CH₂]—ₙ.
聚合物是由许多小单体分子通过共价键连接而成的长链分子。这一过程称为聚合反应。单体通常含有一个官能团或双键，使它们能够相互连接。重复单元显示了聚合后单体的结构，通常括在括号中，加上下标“n”表示大量重复。例如，聚乙烯的重复单元是—[CH₂—CH₂]—ₙ。
Polymers can be homopolymers (made from one type of monomer) or copolymers (made from two or more different monomers). They vary in chain length, branching, and cross‑linking, which all influence physical properties.
聚合物可以是均聚物（由一种单体构成）或共聚物（由两种或更多不同单体构成）。它们在链长、支化和交联方面各有不同，这些都会影响物理性质。
2. Addition Polymerisation | 加成聚合
Addition polymerisation involves monomers that contain a carbon–carbon double bond (C=C). The reaction proceeds via a free‑radical mechanism or an ionic mechanism. The double bond opens up, allowing each monomer molecule to form two new single bonds with neighbouring monomers. No small molecules are eliminated, so the empirical formula of the polymer is identical to that of the monomer.
加成聚合反应涉及含有碳碳双键（C=C）的单体。反应通过自由基机理或离子机理进行。双键打开，使每个单体分子与相邻单体形成两个新的单键。没有小分子被消除，因此聚合物的经验式与单体的经验式相同。
General equation: n CH₂=CHX → —[CH₂—CHX]—ₙ
通式：n CH₂=CHX → —[CH₂—CHX]—ₙ
Common addition polymers include poly(ethene) (PE), poly(propene) (PP), poly(chloroethene) (PVC), and poly(tetrafluoroethene) (PTFE). The properties vary with the substituent X: for example, Cl in PVC gives rigidity and flame retardancy, while F in PTFE creates an extremely chemically resistant, non‑stick material.
常见的加成聚合物包括聚乙烯（PE）、聚丙烯（PP）、聚氯乙烯（PVC）和聚四氟乙烯（PTFE）。性质随取代基 X 的不同而变化：例如 PVC 中的 Cl 提供了刚性和阻燃性，而 PTFE 中的 F 则形成极其耐化学腐蚀且不粘的材料。
Examiners often ask you to draw a section of the polymer chain showing at least two repeat units, starting from the monomer. Remember that the backbone is a continuous carbon chain, with side groups attached as shown in the monomer.
考官经常要求你从单体出发，画出包含至少两个重复单元的聚合物链段。请记住主链是连续的碳链，侧基连接方式与单体所示一致。
3. Condensation Polymerisation | 缩合聚合
Condensation polymerisation involves monomers that each have two functional groups. These monomers react together with the elimination of a small molecule, most commonly water (H₂O) or hydrogen chloride (HCl). The polymer contains a functional group in the backbone, such as an ester or amide linkage. The empirical formula of the polymer is not the same as that of the monomers.
缩合聚合涉及每个单体带有两个官能团。这些单体相互反应，同时消除一个小分子，最常是水（H₂O）或氯化氢（HCl）。聚合物主链中含有官能团，如酯键或酰胺键。聚合物的经验式不同于单体的经验式。
Polyester example: n HOOC–C₆H₄–COOH + n HO–CH₂–CH₂–OH → —[OC–C₆H₄–COO–CH₂–CH₂–O]—ₙ + 2n H₂O
聚酯示例：n HOOC–C₆H₄–COOH + n HO–CH₂–CH₂–OH → —[OC–C₆H₄–COO–CH₂–CH₂–O]—ₙ + 2n H₂O
Two main types of condensation polymers are polyesters (from dicarboxylic acids and diols) and polyamides (from dicarboxylic acids and diamines, or from amino acids). Nylon‑6,6 is a polyamide made from adipic acid (hexanedioic acid) and 1,6‑diaminohexane. PET (polyethylene terephthalate) is a polyester used in bottles and clothing fibres.
两种主要的缩合聚合物是聚酯（由二元羧酸和二元醇制得）和聚酰胺（由二元羧酸和二元胺，或由氨基酸制得）。尼龙‑6,6 是由己二酸和1,6‑己二胺制成的聚酰胺。PET（聚对苯二甲酸乙二酯）是一种用于瓶子和服装纤维的聚酯。
When drawing repeat units for condensation polymers, make sure the ester or amide linkage appears inside the brackets, and that the ends are bonded correctly to avoid dangling bonds. Always count the number of water molecules eliminated.
在绘制缩合聚合物的重复单元时，确保酯键或酰胺键出现在括号内，并且末端键合正确，避免出现悬挂键。务必正确计算消除的水分子数。
4. Types of Polymer Structures | 聚合物结构类型
Polymers can be classified as thermoplastics or thermosets based on their response to heat. Thermoplastics (e.g. PE, PP, PVC, PET) consist of linear or branched chains with weak intermolecular forces between chains. They soften on heating and harden on cooling, making them recyclable. Thermosets (e.g. Bakelite, epoxy resins) contain extensive covalent cross‑links between chains. They do not soften on heating and are strong, rigid, and heat‑resistant, but cannot be remoulded.
聚合物根据对热的响应可分为热塑性和热固性两大类。热塑性塑料（如 PE、PP、PVC、PET）由线性或支化链组成，链间作用力弱。加热时软化，冷却时变硬，因此可回收。热固性塑料（如酚醛树脂、环氧树脂）含有广泛的链间共价交联。加热时不会软化，强度高、刚性好且耐热，但不能重塑。
Elastomers are lightly cross‑linked polymers that can stretch extensively and return to their original shape. The cross‑links prevent irreversible chain slippage. Natural rubber and silicone rubbers are typical elastomers.
弹性体是具有轻微交联的聚合物，可大幅拉伸并恢复原状。交联防止了链的不可逆滑移。天然橡胶和硅橡胶是典型的弹性体。
The degree of crystallinity also affects properties. More linear, unbranched chains pack closely, forming crystalline regions that increase density, stiffness, and chemical resistance. Branched or atactic polymers are more amorphous, transparent, and flexible.
结晶度也影响性质。线性无支化的链堆积更紧密，形成结晶区，从而增加密度、刚度和耐化学性。支化或无规聚合物则更呈无定形态，透明且柔韧。
5. Natural Polymers | 天然聚合物
Natural polymers are produced by living organisms and include proteins, polysaccharides (starch, cellulose, glycogen), and nucleic acids (DNA, RNA). Proteins are condensation polymers of amino acids, linked by peptide (amide) bonds. The primary structure is the sequence of amino acid residues, while secondary and tertiary structures arise from hydrogen bonding, disulfide bridges, and hydrophobic interactions.
天然聚合物由生物体产生，包括蛋白质、多糖（淀粉、纤维素、糖原）和核酸（DNA、RNA）。蛋白质是氨基酸的缩合聚合物，通过肽（酰胺）键连接。一级结构是氨基酸残基的序列，而二级和三级结构则通过氢键、二硫桥和疏水相互作用形成。
Starch and cellulose are both made from glucose monomers, but starch consists of α‑glucose units with a spiral structure (amylose and amylopectin), while cellulose has β‑glucose units with straight chains that hydrogen‑bond extensively, providing high tensile strength for plant cell walls. The difference in glycosidic linkage (α‑1,4 vs β‑1,4) leads to vastly different digestibility and properties.
淀粉和纤维素都由葡萄糖单体构成，但淀粉由 α‑葡萄糖单元构成，呈螺旋结构（直链淀粉和支链淀粉），而纤维素具有 β‑葡萄糖单元，直链间大量氢键交联，为植物细胞壁提供了高拉伸强度。糖苷键的不同（α‑1,4 与 β‑1,4）导致了极不相同的消化性和性质。
DNA is a condensation polymer of nucleotides, each containing deoxyribose sugar, a phosphate group, and a nitrogenous base. The double helix is held together by hydrogen bonds between complementary base pairs (A–T and C–G). Understanding these natural polymers helps link organic chemistry with biochemistry.
DNA 是核苷酸的缩合聚合物，每个核苷酸包含脱氧核糖、磷酸基团和含氮碱基。双螺旋结构通过互补碱基对（A–T 和 C–G）之间的氢键维系。理解这些天然聚合物有助于将有机化学与生物化学联系起来。
6. Synthetic Polymers in Daily Life | 日常生活中的合成聚合物
Addition polymers dominate many everyday applications. Low‑density poly(ethene) (LDPE) is used for plastic bags and films because it is flexible and transparent. High‑density poly(ethene) (HDPE) is stronger and used for bottles and pipes. Poly(propene) is employed in medical syringes, ropes, and carpets due to its toughness and resistance to fatigue. PVC is valued for window frames and pipes (rigid PVC) and in synthetic leather (plasticised PVC). Polystyrene can be solid (transparent containers) or foamed (expanded polystyrene for packaging).
加成聚合物在许多日常应用中占主导地位。低密度聚乙烯（LDPE）用于塑料袋和薄膜，因其柔韧而透明。高密度聚乙烯（HDPE）强度更高，用于瓶子和管道。聚丙烯因韧性好且耐疲劳，被用于医用注射器、绳索和地毯。PVC 因其刚性形式（窗框和管道）和增塑形式（人造革）而受到重视。聚苯乙烯可以是实心的（透明容器）或发泡的（发泡聚苯乙烯用于包装）。
Condensation polymers also find wide use. Nylon‑6,6 is strong and abrasion‑resistant, ideal for ropes, nylon stockings, and mechanical parts. Kevlar, an aromatic polyamide, is bullet‑proof due to extensive hydrogen bonding between chains. PET is transparent and impermeable to carbon dioxide, making it perfect for fizzy drink bottles and polyester fabrics.
缩合聚合物也有广泛应用。尼龙‑6,6 强度高且耐磨，非常适合绳索、尼龙袜和机械零件。凯芙拉是一种芳香族聚酰胺，由于链间广泛的氢键而具有防弹性。PET 透明且不透二氧化碳，非常适合用于汽水瓶和聚酯织物。
You must be able to identify monomers, repeat units, and linkages given a polymer structure, or vice versa, for any of these common materials.
你必须能够根据给定的聚合物结构鉴识单体、重复单元和连接基团，或反过来根据单体推导聚合物结构，针对这些常见材料。
7. Physical Properties: Crystallinity and Branching | 物理性质：结晶度与支化
The arrangement of polymer chains dramatically influences density, tensile strength, transparency, and melting point. Highly linear chains with minimal branching can align closely, forming crystalline regions where intermolecular forces (e.g. van der Waals, dipole‑dipole) are maximised. HDPE is about 80–95% crystalline, making it opaque and rigid. LDPE, with many short and long branches, is only about 40–50% crystalline, leading to flexibility and transparency.
聚合物链的排列方式极大地影响密度、拉伸强度、透明度和熔点。极少支化的高度线性链能紧密排列，形成结晶区，使分子间作用力（如范德华力、偶极‑偶极力）最大化。HDPE 大约 80–95% 结晶，因此不透明且刚性。LDPE 带有许多短支链和长支链，结晶度仅约 40–50%，因此柔韧且透明。
Stereoregularity also matters. Isotactic poly(propene), with all methyl groups on the same side, is a strong semicrystalline material, whereas atactic poly(propene) (random orientation of methyl groups) is amorphous and soft. Catalysts like Ziegler–Natta catalysts control the stereochemistry and thus the properties.
立构规整度也很重要。全同立构聚丙烯，所有甲基都在同侧，是一种坚固的半结晶材料；而无规聚丙烯（甲基无规则取向）则是无定形态且柔软。齐格勒‑纳塔催化剂等可控制立体化学，从而控制性质。
Plasticisers are small molecules added to a polymer to separate chains, reduce intermolecular forces, and increase flexibility. For instance, plasticised PVC is used in cable insulation and artificial leather. Without plasticisers, PVC is rigid and brittle.
增塑剂是添加至聚合物中的小分子，用于分隔链、减少分子间作用力并增加柔韧性。例如，增塑 PVC 用于电缆绝缘层和人造革。没有增塑剂的 PVC 则刚硬且脆。
8. Environmental Impact and Degradability | 环境影响与可降解性
Most addition polymers are non‑biodegradable because their saturated carbon–carbon backbone is chemically very stable and resistant to microbial attack. Discarded plastics accumulate in landfills and oceans, causing long‑term pollution. Microplastics enter the food chain. Incineration can release toxic gases such as HCl from PVC or dioxins if combustion is incomplete.
大多数加成聚合物不可生物降解，因为它们的饱和碳‑碳主链化学性质非常稳定，能抵抗微生物侵蚀。废弃塑料在填埋场和海洋中累积，造成长期污染。微塑料进入食物链。焚烧可能释放有毒气体，如 PVC 产生的 HCl，或在燃烧不完全时产生二噁英。
Some strategies to mitigate this include recycling, development of biodegradable polymers, and feedstock recycling. Biodegradable polymers contain ester or amide linkages that can be broken down by hydrolysis and microorganisms. Examples are poly(lactic acid) (PLA), made from renewable sources such as corn starch, and polyglycolic acid. These are used in compostable packaging and medical sutures.
缓解这一问题的策略包括回收再利用、开发可生物降解聚合物以及原料回收。可生物降解聚合物含有酯键或酰胺键，可被水解和微生物分解。例子有聚乳酸 (PLA)，由玉米淀粉等可再生资源制成，以及聚乙醇酸。这些材料用于可堆肥包装和医用缝合线。
Photodegradable polymers incorporate light‑sensitive functional groups that break the chains upon exposure to UV radiation. However, they may still leave microscopic fragments. In exams, you should be able to discuss the advantages and disadvantages of different disposal methods.
光降解聚合物含有光敏官能团，暴露在紫外线下会断裂链。但它们可能仍会留下微小碎片。在考试中，你应该能够讨论不同处理方法的优缺点。
9. Drawing Repeat Units | 绘制重复单元
Drawing repeat units correctly is a core skill for both IB and CIE papers. For addition polymers, start with the double bond and arrange the monomer so that the carbon atoms of the C=C become the backbone. Draw two carbon atoms joined by a single bond, with the attached groups in the same orientation as in the monomer, and place brackets around it with subscript n. Ensure the bonds leaving the brackets are shown crossing the brackets.
正确绘制重复单元是IB和CIE试卷的核心技能。对于加成聚合物，从双键出发，排列单体使 C=C 的碳原子成为主链。画出两个由单键连接的碳原子，附带的基团朝向与单体一致，用括号括起来并加下标n。确保离开括号的键穿越括号边界。
For condensation polymers, the repeat unit must include the functional linkage (ester —COO— or amide —CONH—). You must reconstruct the backbone, often by combining two monomers while removing small molecules. For instance, in Nylon‑6,6, the repeat unit is —[NH(CH₂)₆NHCO(CH₂)₄CO]—. Always check that the number of atoms agrees with the removal of water molecules.
对于缩合聚合物，重复单元必须包含官能团连接基团（酯 —COO— 或酰胺 —CONH—）。你必须重建主链，通常通过组合两种单体并移除小分子来实现。例如，在尼龙‑6,6中，重复单元为 —[NH(CH₂)₆NHCO(CH₂)₄CO]—。务必核对抗原子数目是否与移除水分子数相符。
Common mistakes include drawing an extra H or missing an O, forgetting to bracket the repeat unit, or drawing only one repeat unit when two are requested. Practise with different monomers until you can draw them fluently.
常见错误包括多画或少画H或O、忘记给重复单元加括号，或在需要画两个重复单元时只画了一个。请用不同单体练习，直到能流畅绘制。
10. Exam Tips and Key Comparisons | 考试技巧与关键对比
| Addition polymerisation | Condensation polymerisation |
| Monomer contains C=C bond | Monomers each have two functional groups |
| No small molecule lost | Small molecule (e.g. H₂O, HCl) eliminated |
| Backbone is all carbon atoms | Backbone contains ester or amide linkages |
| Atom economy theoretically 100% | Lower atom economy due to by‑product |
| Generally non‑biodegradable | Can be biodegradable (ester/amide bonds cleaved) |
Here are some top exam tips:
以下是一些顶级考试技巧：
– When asked to identify a polymer type, check for ester or amide links in the backbone. If present, it is a condensation polymer. If the backbone is purely carbon, it is likely an addition polymer.
– 当被要求判断聚合物类型时，检查主链中是否有酯键或酰胺键。若有，则为缩合聚合物。若主链全是碳，很可能是加成聚合物。
– For environmental questions, link polymer structure to stability: saturated C–C chains resist degradation; ester/amide bonds are hydrolysed. Mention specific examples like PLA.
– 对于环境问题，将聚合物结构与稳定性联系起来：饱和 C–C 链难降解；酯键/酰胺键可水解。提及 PLA 等具体例子。
– In constructing equations, always show two repeating units and bracket them. Label the diagram with the name of the polymer and the small molecule released.
– 在书写方程式时，务必展示两个重复单元并加括号。在图上标注聚合物名称和释放的小分子。
– Use precise terminology: ‘repeat unit’, ‘monomer’, ‘polymerisation’, ‘dicarboxylic acid’, ‘diol’, ‘diamine’. Avoid vague terms like ‘link’ when ‘ester linkage’ or ‘amide linkage’ is more accurate.
– 使用精确术语：“重复单元”、“单体”、“聚合反应”、“二元羧酸”、“二元醇”、“二元胺”。避免模糊词汇，能用“酯键”或“酰胺键”时不用“连接键”。
This guide should give you a firm foundation for tackling any polymer‑related question in IB and CIE Chemistry. Remember to practise drawing structures until they become second nature.
本指南将为你解答 IB 和 CIE 化学中任何与聚合物相关的问题提供坚实的基础。请记住多加练习绘制结构，直至完全自如。
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