Addition Polymers Exam Strategies | 加成聚合物答题策略

📚 Addition Polymers Exam Strategies | 加成聚合物答题策略

Addition polymers are a core topic in CIE A-Level Chemistry. Many students lose marks because they confuse repeat units with monomers or fail to write balanced polymerisation equations. This guide provides a clear, step-by-step exam strategy to help you avoid these errors and answer questions confidently.

加成聚合物是CIE A-Level化学的核心内容。许多学生因为混淆重复单元与单体，或未能写出配平的聚合方程式而失分。本指南提供清晰、分步的答题策略，帮助你避免这些错误，自信应对考试题。

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1. Key Concepts | 核心概念

An addition polymer is formed by the repeated addition of unsaturated monomers, usually alkenes, across a C=C double bond. The polymer contains all the atoms of the original monomers; no small molecule is eliminated.

加成聚合物是由不饱和单体（通常是烯烃）通过反复加成到C=C双键上形成的聚合物。聚合物包含原单体的所有原子，没有小分子生成。

The repeating unit is the simplest group of atoms that repeats along the polymer chain. For example, the repeat unit of poly(ethene) is -CH₂-CH₂-.

重复单元是沿聚合物链重复的最小的原子团。例如，聚乙烯的重复单元是 -CH₂-CH₂-。

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2. Identifying Monomers and Repeat Units | 识别单体与重复单元

To identify the repeat unit from a polymer chain, look for the smallest pattern that repeats. In addition polymers the main chain normally contains two carbon atoms per repeat unit.

要从聚合物链中识别重复单元，寻找最小的重复模式。在加成聚合物中，主链通常每个重复单元包含两个碳原子。

To find the monomer from the repeat unit, convert the single bond between the two main-chain carbons into a C=C double bond. Keep all the substituents exactly as they are.

要从重复单元推断单体，将两个主链碳之间的单键转换为C=C双键。所有取代基保持不变。

For example, the repeat unit [-CH₂-CH(CH₃)-]ₙ gives the monomer CH₂=CHCH₃ (propene).

例如，重复单元 [-CH₂-CH(CH₃)-]ₙ 对应的单体是 CH₂=CHCH₃（丙烯）。

Always show the repeat unit in brackets with the subscript n, and do not forget that end groups are not needed in exam equations.

务必用括号和下标n表示重复单元，考试方程式中端基通常不需要写出。

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3. Writing Polymerisation Equations | 写出聚合反应方程式

Write the equation in the form: n (monomer) → [-repeat unit-]ₙ. The value n is a large integer, so it cannot be cancelled from both sides because monomers are individual molecules while the polymer is one long chain.

将方程式写成：n（单体）→ [-重复单元-]ₙ。n是很大的整数，不能从两边约去，因为单体是单个分子而聚合物是一条长链。

Make sure the atoms on each side balance. For ethene: nCH₂=CH₂ → [-CH₂-CH₂-]ₙ. For chloroethene: nCH₂=CHCl → [-CH₂-CHCl-]ₙ.

确保两边原子守恒。乙烯：nCH₂=CH₂ → [-CH₂-CH₂-]ₙ。氯乙烯：nCH₂=CHCl → [-CH₂-CHCl-]ₙ。

Include conditions if asked: usually high pressure, a catalyst or a free-radical initiator. Common conditions for ethene are high temperature (about 200°C) and high pressure (about 2000 atm), or a catalyst.

如果题目要求，要写出条件：通常是高压、催化剂或自由基引发剂。乙烯的常见条件是高温（约200°C）和高压（约2000 atm），或使用催化剂。

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4. Mechanism of Free-Radical Addition Polymerisation | 自由基加成聚合机理

Free-radical addition polymerisation proceeds in three stages: initiation, propagation and termination.

自由基加成聚合分为三个阶段：引发、增长和终止。

Initiation: heat or UV light breaks the O-O bond in a peroxide (ROOR) to give two alkoxy radicals R•. The radical attacks the alkene π bond, forming a carbon radical.

引发：加热或紫外光使过氧化物（ROOR）中的O-O键断裂，产生两个烷氧自由基R•。自由基进攻烯烃的π键，生成碳自由基。

Propagation: the new radical attacks another monomer molecule, and the chain grows as this step repeats many times.

增长：新的自由基进攻另一个单体分子，链不断增长，该步骤重复许多次。

Termination: two radicals combine, or one radical transfers a hydrogen atom to another. The polymer chain stops growing.

终止：两个自由基结合，或一个自由基向另一个自由基转移氢原子。聚合物链停止增长。

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5. Polymer Structure: Linear, Branched, Cross-linked | 聚合物结构：线型、支化、交联

Linear

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