📚 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。
1. Key Concepts | 核心概念
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-。
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。
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。
3. Writing Polymerisation Equations | 写出聚合反应方程式
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。
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。
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。
5. Polymer Structure: Linear, Branched, Cross-linked | 聚合物结构：线型、支化、交联
Linear
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