Addition polymers

Chemistry· 35 min read

1. 1. What is Addition Polymerization?★★☆☆☆⏱ 10 min

📘 Definition

Addition Polymerization

A reaction where many small alkene-based monomer molecules add together to form a large polymer chain, with no small by-products produced.

Example:

Ethene monomers joining to form polyethene

Unlike condensation polymerization, addition polymerization only requires monomers with at least one carbon-carbon double bond. All atoms from the original monomers are retained in the final polymer, with no elimination of small molecules like water or hydrogen chloride.

📐 Worked Example

Show the formation of polypropene from propene monomers and write its repeating unit.

1
1. Start with the structure of the propene monomer:
2
$CH_2=CH(CH_3)$
3
1. Break the carbon-carbon double bond to create open bonding sites on each carbon:
4
$\bullet CH_2-CH(CH_3) \bullet$
5
1. Link the activated units together repeatedly to form a long polymer chain:
6
$...-CH_2-CH(CH_3)-CH_2-CH(CH_3)-CH_2-CH(CH_3)-...$
7
1. Draw the simplified repeating unit for exam use:
8
$\ce{-[CH2-CH(CH3)]_n-}$

Exam tip:

Always draw bonds extending through the brackets of a repeating unit to show it connects to adjacent units. Examiners regularly penalize missing outer bonds.

2. 2. Drawing Repeating Units From Monomers★★☆☆☆⏱ 12 min

For any alkene monomer with the general formula $C H_{2} = C H R$ , where R is any substituent group (alkyl, aryl, halogen etc.), the repeating unit follows a consistent pattern: the double bond breaks, R stays attached to its original carbon, and the two carbons from the double bond form the backbone of the repeating unit.

📐 Worked Example

Draw the repeating unit of poly(vinyl chloride) (PVC) from its monomer $C H_{2} = C H C l$ .

1
1. Locate the carbon-carbon double bond in the monomer, confirm the Cl substituent is attached to one carbon of the double bond.
2
1. Break the double bond to form two open single bonds on the backbone carbons.
3
1. Keep the Cl substituent attached to its original carbon, enclose the two-carbon backbone in brackets, add extending bonds and n subscript.
4
Final correct repeating unit:
5
$\ce{-[CH2-CH(Cl)]_n-}$

✓ Quick check

Test your understanding:

What is the correct repeating unit of polystyrene, formed from monomer $C H_{2} = C H (C_{6} H_{5})$ ?
- A: $\ce - [C H 2 - C H (C 6 H 5)]_{n} -$
- B: $\ce - [C H (C 6 H 5) - C H (C 6 H 5)]_{n} -$
- C: $\ce - [C H 2 - C H 2 - C 6 H 5]_{n} -$
Reveal answer
A: $\ce{-[CH2-CH(C6H5)]_n-}$ —
Correct! The phenyl group stays attached to the original carbon from the double bond.

3. 3. Identifying Monomers From Repeating Units★★★☆☆⏱ 15 min

A common exam question asks you to work backwards from a given repeating unit to find the original alkene monomer. The process is simply the reverse of polymerization: split the polymer backbone between the bonds connecting adjacent repeating units, then reform the double bond between the two carbons of the backbone.

📐 Worked Example

Identify the monomer of the addition polymer with repeating unit $\ce - [C H 2 - C (C H 3) 2]_{n} -$ .

1
1. Split the backbone between the carbon atoms that connect to adjacent repeating units, leaving you with the fragment $C H_{2} - C (C H_{3})_{2}$ .
2
1. Reform the double bond between these two carbons, which was the original double bond in the monomer.
3
1. The final monomer is:
4
$CH_2=C(CH_3)_2 (2-methylpropene)$

Exam tip:

The molecular formula of the monomer is identical to the molecular formula of the repeating unit for addition polymers. Use this to check your answer if you are unsure.

4. 4. Common Addition Polymers and Uses★★☆☆☆⏱ 8 min

CIE exams regularly test recall of the names, monomers and common uses of the major commercial addition polymers, as shown in the table below:

Polymer Name	Monomer Name	Common Use
Polyethene (PE)	Ethene	Plastic bags, food packaging
Polypropene (PP)	Propene	Ropes, crates, synthetic fibres
Poly(vinyl chloride) (PVC)	Chloroethene (vinyl chloride)	Pipes, window frames, electrical insulation
Polystyrene (PS)	Phenylethene (styrene)	Packaging foam, disposable containers
Polytetrafluoroethene (PTFE)	Tetrafluoroethene	Non-stick coatings, low-friction bearings

5. Common Pitfalls

Wrong move:

Drawing a repeating unit without extending bonds through the brackets

Why:

Examiners require this to show the repeating unit connects to the rest of the chain, and will deduct marks for missing bonds

Correct move:

Always draw a single bond extending out of each side of the brackets, and add the n subscript

Wrong move:

Moving the substituent R when drawing the repeating unit, e.g. writing polypropene as $\ce - [C H 2 - C H 2 - C H 2]_{n} -$

Why:

Confuses addition polymer backbone structure with straight-chain alkanes, forgetting R stays attached to the original double bond carbon

Correct move:

Keep all substituents in their original position relative to the two double bond carbons after breaking the double bond

Wrong move:

Stating addition polymerization produces a small by-product like water

Why:

Confuses addition polymerization with condensation polymerization, a common exam trick question

Correct move:

Addition polymerization produces no by-products; all atoms from monomers end up in the polymer chain

Wrong move:

Identifying a monomer with more than one double bond from a 2-carbon repeating unit

Why:

Incorrectly splitting the polymer backbone over more than two carbons

Correct move:

For addition polymers from monalkene monomers, split the backbone every 2 carbons then reform the double bond between those two carbons

Wrong move:

Writing the monomer of PTFE as $C H_{2} = C F_{2}$

Why:

Misremembering the structure of this common addition polymer

Correct move:

PTFE is made from tetrafluoroethene $C F_{2} = C F_{2}$ , with all four positions on the double bond substituted with fluorine

6. Quick Reference Cheatsheet

Task	Step-by-Step Rule
Draw repeating unit from monomer	Locate C=C in monomer 2. Break double bond to single 3. Add extending bonds to each end 4. Enclose in brackets, add n
Find monomer from repeating unit	Split chain between adjacent units 2. Reform C=C between 2 backbone carbons 3. Result is the monomer
Key facts	No by-products formed, all monomers have C=C, molecular formula of monomer = formula of repeating unit
Common polymers	PE: ethene → polyethene, PVC: chloroethene → PVC, PTFE: CF₂=CF₂ → PTFE

When this came up on past exams

AI-estimated based on syllabus patterns — cross-check with official past papers for accuracy. Use only as revision-focus signals.

2022 · 12
Identify monomer from given polymer
2023 · 22
Draw repeating unit from alkene monomer
2021 · 31
Compare addition vs condensation polymerization

Going deeper

syllabusCIE 9701 2025-2026 SyllabusSee section 24 for full polymer syllabus

What's Next

Addition polymers are the foundational polymer type in the CIE A-Level polymers unit, and the core skills of drawing repeating units and identifying monomers are required for all subsequent polymer topics. Most CIE exam papers include at least one question testing these skills, so mastering this sub-topic guarantees you easy, guaranteed marks on exam day. This knowledge also sets you up to compare addition polymers with condensation polymers, the second major polymer class, and prepares you for questions on polymer properties, biodegradability and disposal which are often tested in extended response questions.