Types and Applications of Polymerization Reactions | 聚合反应的类型与应用

📚 Types and Applications of Polymerization Reactions | 聚合反应的类型与应用

Polymerization is a fundamental process in organic chemistry in which small molecules known as monomers join together to form large macromolecules called polymers. Understanding the types of polymerization and their real-world applications is essential for success in A-Level chemistry examinations.

聚合反应是有机化学中的一个基本过程，即称为单体的小分子相互连接形成称为聚合物的大分子。理解聚合反应的类型及其实际应用，对于在A-Level化学考试中取得好成绩至关重要。

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1. Overview of Polymerization | 聚合反应概述

Polymers are long-chain molecules composed of repeating structural units derived from monomers. The process of forming these chains can be classified primarily into two major categories: addition polymerization and condensation polymerization. Each type follows a distinct mechanism and has unique characteristics.

聚合物是由单体衍生而来的重复结构单元组成的长链分子。形成这些链的过程主要可分为两大类：加聚反应和缩聚反应。每种类型遵循不同的机理，并具有独特的特征。

The key differences between the two types can be summarised as follows:

这两种类型之间的关键区别可总结如下：

Feature | 特征	Addition Polymerisation | 加聚反应	Condensation Polymerisation | 缩聚反应
Monomer type | 单体类型	Alkenes with C=C bonds | 含C=C键的烯烃	Bifunctional molecules (diols, diamines, diacids) | 双官能团分子（二醇、二胺、二酸）
Small molecule lost | 失去的小分子	None | 无	Water, HCl, etc. | 水、氯化氢等
Mechanism | 机理	Chain growth (free radical, cationic, anionic) | 链增长（自由基、阳离子、阴离子）	Step growth | 逐步增长
Examples | 实例	Polyethene, PVC, polystyrene | 聚乙烯、聚氯乙烯、聚苯乙烯	Nylon, Terylene (polyester) | 尼龙、涤纶（聚酯）

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2. Addition Polymerisation | 加聚反应

Addition polymerisation involves the repetitive addition of alkene monomers that contain a carbon-carbon double bond. The double bond opens up to form single bonds, allowing monomers to link together without the elimination of any small molecule.

加聚反应涉及含有碳碳双键的烯烃单体的重复加成。双键打开形成单键，使单体无需消除任何小分子即可连接在一起。

The general equation for addition polymerisation can be written as:

加聚反应的一般方程式可写为：

n CH₂=CH₂ → —(CH₂—CH₂)ₙ—

For ethene, the polymer formed is polyethene (also called polythene). The monomer ethene has the formula C₂H₄, and each repeating unit in the polymer is —CH₂—CH₂—.

对于乙烯，形成的聚合物是聚乙烯。乙烯单体的分子式为C₂H₄，聚合物中每个重复单元为—CH₂—CH₂—。

Key features of addition polymerisation include:

加聚反应的关键特征包括：

• The polymer is the only product; no by-products are formed. | 聚合物是唯一产物；不形成副产物。

• The empirical formula of the polymer is identical to that of the monomer. | 聚合物的实验式与单体的实验式相同。

• The reaction requires an initiator, typically a free radical. | 反应需要引发剂，通常是自由基。

• High pressure and/or catalysts may be required depending on the monomer. | 根据单体的不同，可能需要高压和/或催化剂。

Substituted alkenes can also undergo addition polymerisation. For example, chloroethene (CH₂=CHCl) polymerises to form poly(chloroethene), commonly known as PVC. Similarly, phenylethene (CH₂=CHC₆H₅) forms polystyrene, and propene (CH₂=CHCH₃) forms polypropene.

取代烯烃也可以发生加聚反应。例如，氯乙烯（CH₂=CHCl）聚合形成聚氯乙烯，通常称为PVC。类似地，苯乙烯（CH₂=CHC₆H₅）形成聚苯乙烯，丙烯（CH₂=CHCH₃）形成聚丙烯。

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3. Mechanism of Addition Polymerisation | 加聚反应的机理

A-Level syllabuses typically require knowledge of the free-radical mechanism for addition polymerisation. This mechanism proceeds in three stages: initiation, propagation, and termination.

A-Level课程大纲通常要求掌握加聚反应的自由基机理。该机理分三个阶段进行：链引发、链增长和链终止。

Stage 1: Initiation | 第一阶段：链引发

An initiator such as benzoyl peroxide or an organic peroxide decomposes to form free radicals. The general homolytic fission can be represented as:

引发剂如过氧化苯甲酰或有机过氧化物分解产生自由基。均裂的一般表示如下：

RO—OR → 2 RO•

The free radical (RO•) then attacks the π bond of an alkene monomer, forming a new carbon-centred radical:

然后自由基（RO•）攻击烯烃单体的π键，形成新的碳中心自由基：

RO• + CH₂=CH₂ → RO—CH₂—CH₂•

Stage 2: Propagation | 第二阶段：链增长

The radical at the end of the growing chain attacks another monomer molecule, adding one unit at a time. This step repeats rapidly, building a long polymer chain:

生长链末端的自由基攻击另一个单体分子，一次添加一个单元。此步骤快速重复，构建长聚合物链：

RO—(CH₂—CH₂)ₙ—CH₂—CH₂• + CH₂=CH₂ → RO—(CH₂—CH₂)ₙ₊₁—CH₂—CH₂•

Stage 3: Termination | 第三阶段：链终止

Two propagating radicals combine, or a radical transfers a hydrogen atom, ending the growth of the chain. Combination of two growing chains gives a single longer chain.

两个增长中的自由基结合，或一个自由基转移一个氢原子，从而终止链的增长。两个增长链结合形成一条更长的链。

~CH₂—CH₂• + •CH₂—CH₂~ → ~CH₂—CH₂—CH₂—CH₂~

It is important to note that the polymer chains produced by free-radical polymerisation have varying lengths, so the polymer sample is a mixture of molecules with different molar masses. This is expressed as an average molar mass.

需要注意，自由基聚合产生的聚合物链长度不同，因此聚合物样品是不同摩尔质量分子的混合物。这用平均摩尔质量来表示。

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4. Condensation Polymerisation | 缩聚反应

Condensation polymerisation involves bifunctional monomers — molecules that possess two reactive functional groups — reacting together with the elimination of a small molecule, such as water or hydrogen chloride. Each step in the process joins two monomers while releasing a by-product.

缩聚反应涉及双官能团单体——即具有两个反应性官能团的分子——在消除小分子（如水或氯化氢）的同时相互反应。该过程的每一步连接两个单体并释放副产物。

Two important classes of condensation polymers are polyamides and polyesters.

两类重要的缩聚聚合物是聚酰胺和聚酯。

Polyamides | 聚酰胺

Polyamides are formed from the reaction between a dicarboxylic acid and a diamine. The functional groups react to form amide linkages (−CO−NH−) with the loss of water.

聚酰胺由二羧酸和二胺之间的反应形成。官能团反应形成酰胺键（−CO−NH−），同时失去水。

Nylon-6,6 is a well-known polyamide formed from hexanedioic acid (adipic acid) and 1,6-diaminohexane. The “6,6” refers to the six carbon atoms in each monomer.

尼龙-6,6是一种众所周知的聚酰胺，由己二酸和1,6-己二胺形成。”6,6″指的是每个单体中的六个碳原子。

The repeating unit of nylon-6,6 contains the amide linkage:

尼龙-6,6的重复单元含有酰胺键：

—[—NH—(CH₂)₆—NH—CO—(CH₂)₄—CO—]ₙ—

Polyesters | 聚酯

Polyesters are formed from the reaction between a dicarboxylic acid and a diol, producing ester linkages (−COO−) with the loss of water.

聚酯由二羧酸和二醇之间的反应形成，产生酯键（−COO−），同时失去水。

Terylene (also called Dacron) is a common polyester produced from benzene-1,4-dicarboxylic acid (terephthalic acid) and ethane-1,2-diol (ethylene glycol).

涤纶（也称大可纶）是一种常见的聚酯，由对苯二甲酸和乙二醇制备。

—[—O—CH₂—CH₂—O—CO—C₆H₄—CO—]ₙ—

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5. Monomers and Repeating Units | 单体与重复单元

A critical skill in exam questions is the ability to identify the monomer from a given polymer structure, and conversely, to deduce the repeating unit from a given monomer. The repeating unit is the smallest group of atoms that repeats along the polymer chain.

考试题中的一个关键技能是能够从给定的聚合物结构识别单体，反之亦然，从给定的单体推导重复单元。重复单元是沿聚合物链重复的最小原子组。

For addition polymers, the repeating unit has the same atoms as the monomer, but the double bond is converted to single bonds. To find the monomer from the repeating unit, add back the double bond.

对于加聚物，重复单元与单体具有相同的原子，但双键转化为单键。要从重复单元找单体，需要恢复双键。

For example, the repeating unit of polypropene is:

例如，聚丙烯的重复单元为：

—CH₂—CH(CH₃)—

Adding the double bond back between the two carbon atoms gives the monomer CH₂=CHCH₃ (propene).

在两个碳原子之间恢复双键，得到单体CH₂=CHCH₃（丙烯）。

For condensation polymers, the repeating unit includes contributions from both monomers. The identification of monomers requires recognising the amide or ester linkage and splitting it apart, adding back −OH to one fragment and −H to the other:

对于缩聚物，重复单元包含来自两个单体的贡献。识别单体需要识别酰胺键或酯键并将其拆分，向一个片段加回−OH，向另一个片段加回−H：

—CO—NH— (amide) → —COOH + H₂N—

—CO—O— (ester) → —COOH + HO—

Students must practise these conversions thoroughly as they appear frequently in structured examination questions.

学生必须充分练习这些转换，因为它们在结构化的考试问题中频繁出现。

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6. Comparison of Addition and Condensation Polymerisation | 加聚反应与缩聚反应的对比

Understanding the similarities and differences between the two types is essential for answering comparison questions. The table below summarises the most important points.

理解两种类型之间的相似之处和差异对于回答比较类问题至关重要。下表总结了最重要的要点。

Aspect | 方面	Addition | 加聚	Condensation | 缩聚
Monomers | 单体	Alkenes (one type) | 烯烃（一种）	Two types with two functional groups each | 两种类型，各含两个官能团
By-product | 副产物	None | 无	Small molecule (H₂O, HCl) | 小分子（H₂O、HCl）
Bond formed | 形成的键	C—C single bond | 碳碳单键	Amide or ester linkage | 酰胺键或酯键
Atom economy | 原子经济性	100% | 100%	Less than 100% (by-product formed) | 低于100%（形成副产物）
Thermoplastic behaviour | 热塑性行为	Usually thermoplastic | 通常是热塑性的	Often thermoplastic | 通常是热塑性的

The concept of atom economy links polymerisation to the broader theme of green chemistry. Addition polymerisation has 100% atom economy, making it inherently more sustainable than condensation polymerisation.

原子经济性的概念将聚合反应与绿色化学的更广泛主题联系起来。加聚反应具有100%的原子经济性，使其本质上比缩聚反应更具可持续性。

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7. Applications of Addition Polymers | 加聚物的应用

Addition polymers are among the most widely produced synthetic materials in the world, with applications ranging from packaging to construction.

加聚物是世界上产量最广泛的合成材料之一，其应用范围从包装到建筑。

Polyethene (Polythene) | 聚乙烯

Polyethene exists in different forms — low-density polyethene (LDPE) and high-density polyethene (HDPE). LDPE has branched chains, making it flexible and transparent, suitable for plastic bags and squeezable bottles. HDPE has linear chains, giving it higher strength and stiffness, used for rigid containers and piping.

聚乙烯存在不同形式——低密度聚乙烯（LDPE）和高密度聚乙烯（HDPE）。LDPE具有支链，使其柔韧且透明，适用于塑料袋和可挤压瓶子。HDPE具有线性链，赋予其更高的强度和刚度，用于刚性容器和管道。

Polyvinyl Chloride (PVC) | 聚氯乙烯

PVC is rigid and durable. It is widely used for window frames, drainage pipes, and electrical cable insulation. Plasticisers can be added to PVC to make it flexible for use in synthetic leather and waterproof clothing.

PVC坚硬且耐用。它广泛用于窗框、排水管和电线绝缘层。可以向PVC中添加增塑剂使其柔韧，用于合成革和防水服装。

Polystyrene | 聚苯乙烯

Polystyrene is a hard, transparent plastic used in disposable cutlery and CD cases. Expanded polystyrene (foam) is an excellent thermal insulator used in packaging and building insulation.

聚苯乙烯是一种坚硬、透明的塑料，用于一次性餐具和CD盒。发泡聚苯乙烯（泡沫）是极好的隔热材料，用于包装和建筑保温。

Polytetrafluoroethene (PTFE) | 聚四氟乙烯

PTFE, known commercially as Teflon, has exceptionally low friction and high chemical resistance, making it ideal for non-stick cookware and industrial seals.

PTFE，商业上称为特氟龙，具有极低的摩擦系数和高耐化学性，使其成为不粘炊具和工业密封件的理想材料。

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8. Applications of Condensation Polymers | 缩聚物的应用

Condensation polymers such as nylon and polyesters have revolutionised the textile and engineering industries. Their strong intermolecular forces, particularly hydrogen bonding in polyamides, give them high tensile strength.

尼龙和聚酯等缩聚物彻底改变了纺织和工程行业。它们强大的分子间作用力，特别是聚酰胺中的氢键，赋予它们高抗拉强度。

Nylon | 尼龙

• Textiles: Nylon fibres are used in clothing, ropes, and seat belts due to their strength and elasticity. | 纺织品：尼龙纤维因其强度和弹性而用于服装、绳索和安全带。

• Engineering: Nylon gears and bearings are used in machinery because of their wear resistance and low friction. | 工程：尼龙齿轮和轴承因其耐磨性和低摩擦系数而用于机械。

• Consumer goods: Toothbrush bristles and fishing lines are commonly made from nylon. | 消费品：牙刷毛和钓鱼线通常由尼龙制成。

Terylene (Polyester) | 涤纶（聚酯）

• Fabrics: Terylene is used extensively in clothing, often blended with cotton. It is crease-resistant and dries quickly. | 织物：涤纶广泛用于服装，常与棉混纺。其抗皱且快干。

• Packaging: PET (polyethylene terephthalate), a close relative of Terylene, is used to make drinks bottles. | 包装：PET（聚对苯二甲酸乙二醇酯）是涤纶的近亲，用于制造饮料瓶。

• Industrial applications: Polyester fibres reinforce conveyor belts and are used in tyre cords. | 工业应用：聚酯纤维增强传送带，并用于轮胎帘线。

Kevlar | 凯夫拉

Kevlar is an aromatic polyamide with extremely high strength-to-weight ratio. It is used in bulletproof vests, helmets, and high-performance composites for aerospace applications.

凯夫拉是一种芳香族聚酰胺，具有极高的强度重量比。它用于防弹背心、头盔和航空航天应用的高性能复合材料。

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9. Structure–Property Relationships | 结构–性能关系

Examination questions frequently ask you to explain physical properties of polymers in terms of their molecular structure. The following factors are crucial.

考试问题经常要求你从分子结构的角度解释聚合物的物理性质。以下因素至关重要。

Chain length | 链长

Longer polymer chains lead to stronger intermolecular forces (more London dispersion forces) and therefore higher tensile strength, melting point, and rigidity. Short chains tend to form weaker, less durable materials.

较长的聚合物链导致更强的分子间作用力（更多的伦敦色散力），因此具有更高的抗拉强度、熔点和刚性。短链往往形成较弱、不太耐用的材料。

Branched vs linear chains | 支链与线性链

Linear chains pack closely together, maximising intermolecular contacts and giving high density and crystallinity. Branched chains cannot pack as tightly, resulting in lower density, lower melting points, and greater flexibility.

线性链紧密堆积在一起，使分子间接触最大化，赋予高密度和高结晶度。支链不能如此紧密地堆积，导致密度较低、熔点较低且柔韧性更高。

Cross-linking | 交联

Cross-links are covalent bonds between adjacent polymer chains. Low-density polyethene can be cross-linked to improve its strength. Heavily cross-linked polymers are thermosetting — they cannot be melted and reshaped once formed.

交联是相邻聚合物链之间的共价键。低密度聚乙烯可以交联以提高其强度。高度交联的聚合物是热固性的——一旦形成就无法熔化重塑。

Intermolecular hydrogen bonding | 分子间氢键

Polyamides such as nylon contain −CO−NH− groups that form hydrogen bonds between adjacent chains. These strong interactions give nylon its characteristic toughness and relatively high melting point. Polyesters only have dipole-dipole interactions, making them slightly weaker in comparison.

尼龙等聚酰胺含有−CO−NH−基团，可在相邻链之间形成氢键。这些强相互作用赋予尼龙特有的韧性和相对较高的熔点。聚酯只有偶极-偶极相互作用，因此相比之下稍弱。

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10. Environmental Considerations | 环境考量

The widespread use of synthetic polymers has raised significant environmental concerns. A-Level students are expected to discuss these issues and their possible solutions.

合成聚合物的广泛使用引发了重大环境问题。A-Level学生应能够讨论这些问题及其可能的解决方案。

Non-biodegradability | 不可生物降解性

Most addition polymers, particularly polyethene and PVC, are non-biodegradable. They persist in the environment for hundreds of years, contributing to landfill waste and ocean pollution.

大多数加聚物，特别是聚乙烯和PVC，是不可生物降解的。它们在环境中持续存在数百年，造成垃圾填埋场废物和海洋污染。

Solutions | 解决方案

• Recycling: Polymer waste can be separated and mechanically recycled into new products. However, mixed plastics are difficult to recycle economically. | 回收：聚合物废物可以被分类并机械回收成新产品。然而，混合塑料在经济上难以回收。

• Biodegradable polymers: Polylactic acid (PLA) and polyhydroxyalkanoates (PHAs) are biodegradable polyesters derived from renewable sources. They can be broken down by microorganisms. | 可生物降解聚合物：聚乳酸（PLA）和聚羟基烷酸酯（PHA）是可生物降解的聚酯，来源于可再生资源。它们可以被微生物分解。

• Feedstock recycling: Chemical processes can convert polymer waste back into monomers or fuels. | 原料回收：化学过程可以将聚合物废物转化回单体或燃料。

• Reduction and reuse: Reducing single-use plastic consumption and designing reusable packaging remain the most effective strategies. | 减量和重复使用：减少一次性塑料消费和设计可重复使用的包装仍然是最有效的策略。

Photodegradable polymers, which incorporate light-sensitive groups that break down under sunlight, offer another route to reducing plastic persistence in the environment.

可光降解聚合物含有光敏基团，在阳光下降解，这提供了减少塑料在环境中持久性的另一途径。

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11. Exam Tips and Common Mistakes | 考试技巧与常见错误

Many students lose marks on polymerisation questions due to avoidable errors. The following advice will help you maximise your score.

许多学生在聚合反应问题上因可避免的错误而失分。以下建议将帮助你最大化得分。

Tip 1: Draw repeating units with brackets | 技巧一：用方括号画重复单元

Always draw the repeating unit with the bracket notation and include the subscript n to indicate that the chain repeats many times. Do not forget the extended bond lines extending through the brackets.

始终使用方括号符号绘制重复单元，并包含下标n以表示链重复多次。不要忘记延伸穿过方括号的键线。

Tip 2: Do not confuse empirical formula with repeating unit | 技巧二：不要混淆实验式与重复单元

For addition polymers, the empirical formula is the same as the monomer formula, but the repeating unit is a structural representation, not just a molecular formula. Always show full structural details.

对于加聚物，实验式与单体式相同，但重复单元是结构表示，不仅仅是分子式。始终展示完整的结构细节。

Tip 3: Identify functional group linkages correctly | 技巧三：正确识别官能团连接

In condensation polymers, the amide linkage is −CO−NH− and the ester linkage is −CO−O−. When writing monomers, remember to show the carboxylic acid end as −COOH and the amine as −NH₂ or alcohol as −OH.

在缩聚物中，酰胺键为−CO−NH−，酯键为−CO−O−。在写单体时，记住将羧酸端表示为−COOH，胺表示为−NH₂，醇表示为−OH。

Tip 4: State conditions required | 技巧四：说明所需条件

When describing polymerisation, include relevant conditions: high pressure and a Ziegler-Natta catalyst for polyethene production; concentrated sulfuric acid as a catalyst for esterification in polyester formation; and high temperature for nylon production.

在描述聚合反应时，包括相关条件：聚乙烯生产需要高压和齐格勒-纳塔催化剂；聚酯形成中的酯化需要浓硫酸作为催化剂；尼龙生产需要高温。

Common mistake: Forgetting the by-product | 常见错误：忘记副产物

In condensation polymerisation, always write the small molecule (H₂O or HCl) as a product. Failing to do so is a frequent source of lost marks. In addition polymerisation, ensure no by-product is written.

在缩聚反应中，始终将小分子（H₂O或HCl）写为产物。未这样做是常见的失分原因。在加聚反应中，确保不写副产物。

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12. Summary | 总结

Polymerisation is a central topic in A-Level organic chemistry. Addition polymerisation joins alkene monomers without losing any atoms, giving a 100% atom economy. Condensation polymerisation joins bifunctional monomers with the loss of a small molecule, forming polyamides and polyesters with characteristic functional group linkages.

聚合反应是A-Level有机化学的核心主题。加聚反应在不损失任何原子的情况下连接烯烃单体，具有100%的原子经济性。缩聚反应在失去一个小分子的同时连接双官能团单体，形成具有特征性官能团连接的聚酰胺和聚酯。

The properties of polymers — strength, flexibility, melting point, and chemical resistance — are determined by molecular factors such as chain length, branching, cross-linking, and intermolecular forces. These properties, in turn, determine the practical applications of each polymer, from everyday packaging to advanced aerospace materials.

聚合物的性质——强度、柔韧性、熔点和耐化学性——由链长、支化、交联和分子间作用力等分子因素决定。这些性质反过来决定了每种聚合物的实际应用，从日常包装到先进的航空航天材料。

Finally, environmental concerns surrounding polymer waste highlight the importance of recycling, biodegradable alternatives, and sustainable design. Mastering the types, mechanisms, applications, and environmental implications of polymerisation will enable you to answer both factual and analytical examination questions with confidence.

最后，围绕聚合物废物的环境问题凸显了回收、可生物降解替代品和可持续设计的重要性。掌握聚合反应的类型、机理、应用和环境意义，将使你能够自信地回答事实性和分析性的考试问题。

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Published by TutorHao | Chemistry Revision Series | aleveler.com

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