Synthetic polymers

Q: What is the difference between a monomer and a polymer?

A monomer is a small, simple molecule that acts as a single repeating unit, whereas a polymer is a large macromolecule formed when many monomers chemically join together.

Q: What occurs during addition polymerisation?

Unsaturated monomers containing carbon-carbon double bonds ("> ext{C}= ext{C}<") open their double bonds to form a single long polymer chain of single bonds, producing no other byproduct.

Q: How do you draw the repeat unit of an addition polymer from its monomer?

Replace the \(\text{C}= ext{C}\) double bond with a single \(\text{C}-\text{C}\) bond, keep attached groups in the same positions, and draw extension bonds extending horizontally through square brackets with a subscript \(n\).

Q: What are the monomers and repeat units of the four prescribed addition polymers: poly(ethene), poly(propene), poly(chloroethene), and poly(tetrafluoroethene)?

Poly(ethene): \(\text{CH}_2=\text{CH}_2 \rightarrow -[\text{CH}_2-\text{CH}_2]_n-\); Poly(propene): \(\text{CH}_2=\text{CH}-\text{CH}_3 \rightarrow -[\text{CH}_2-\text{CH}(\text{CH}_3)]_n-\); Poly(chloroethene): \(\text{CH}_2=\text{CHCl} \rightarrow -[\text{CH}_2-\text{CH(Cl)}]_n-\); Poly(tetrafluoroethene): \(\text{CF}_2=\text{CF}_2 \rightarrow -[\text{CF}_2-\text{CF}_2]_n-\).

Q: How can you deduce the monomer from a given addition polymer repeat unit?

Identify the two-carbon backbone of the repeat unit, remove the extension bonds and brackets, and replace the single \(\text{C}-\text{C}\) bond with a \(\text{C}=\text{C}\) double bond.

Q: Why are addition polymers non-biodegradable and difficult to dispose of in landfills?

Addition polymers are chemically inert because of their strong, unreactive \(\text{C}-\text{C}\) single bonds, meaning microorganisms cannot break them down naturally.

Q: What environmental problems are associated with the incineration of synthetic addition polymers?

Incineration produces carbon dioxide (a greenhouse gas), toxic carbon monoxide from incomplete combustion, and hazardous acidic gases such as hydrogen chloride (\(\text{HCl}\)) from chlorine-containing polymers like PVC.

Q: What is condensation polymerisation?

Condensation polymerisation is a reaction where monomers with two functional groups combine to form a polymer chain, eliminating a small molecule such as water (\(\text{H}_2\text{O}\)) at each linkage.

Q: Which two types of monomers react to form a polyester, and what linkage connects them?

A dicarboxylic acid (containing two \(-\text{COOH}\) groups) and a diol (containing two \(-\text{OH}\) groups) react to form ester linkages (\(-\text{COO}-\)) and water.

Q: What is the repeat unit formed from the condensation polymerisation of ethanedioic acid and ethanediol?

The repeat unit is \(-[\text{O}-\text{CH}_2-\text{CH}_2-\text{O}-\text{CO}-\text{CO}]_n-\), producing \(2n\) molecules of \(\text{H}_2\text{O}\) as a byproduct.

Practice

Chemistry · Pearson Edexcel IGCSE · 5 min read · Updated: Sep 12, 2026

Welcome to Synthetic Polymers! Your Chemistry Survival Guide

Hello future chemists! Get ready to dive into the amazing world of polymers. Don't worry if the name sounds complicated; you interact with polymers every single day—we’re talking about plastics, packaging, non-stick coatings, fabrics, and bottles.

This chapter connects the small organic molecules we’ve studied (like alkenes, carboxylic acids, and alcohols) to the large, useful materials that make up modern society. Understanding how these massive molecules are built and disposed of is a key part of organic chemistry.

What You Will Learn:

What monomers and polymers are.
How addition polymerisation works and the repeat units of poly(ethene), poly(propene), poly(chloroethene), and poly(tetrafluoroethene).
How to deduce a monomer from a polymer repeat unit and vice versa.
Disposal problems: inertness, inability to biodegrade, and toxic gases when burned.
(Paper 2) Condensation polymerisation to form polyesters, including ethanedioic acid with ethanediol, and biodegradable biopolyesters.

1. Monomers, Polymers, and Polymerisation: The Building Blocks

Key Definitions

Imagine you have a box full of identical small Lego bricks. Now imagine you snap them all together to form a very long chain.

1. Monomer:
A monomer (mono- means ‘one’) is a small, simple molecule that acts as the basic repeating unit.
Analogy: A single Lego brick.

2. Polymer:
A polymer (poly- means ‘many’) is a large molecule (macromolecule) formed when many small monomers join together.
Analogy: The long chain built from many Lego bricks.

3. Polymerisation:
The chemical reaction in which many monomers join together to form a polymer chain.

2. Addition Polymerisation

In addition polymerisation, thousands of unsaturated monomers containing a carbon-carbon double bond ( \(>\text{C}=\text{C}<\) ) join together to form a single long polymer chain. No other product is formed.

How Addition Polymerisation Works

The double bond between carbon atoms in the monomer breaks (opens up).
Each carbon atom forms a new single covalent bond to a carbon atom on an adjacent monomer.
This links thousands of monomer units into a continuous chain of single \(\text{C}-\text{C}\) bonds.

Representing Addition Polymers: Monomers and Repeat Units

A repeat unit is the specific arrangement of atoms in the polymer that is repeated over and over. When drawing a repeat unit:

Replace the \(\text{C}=\text{C}\) double bond with a single \(\text{C}-\text{C}\) bond.
Keep all the atoms or groups attached to each carbon atom in the exact same positions above and below the chain.
Extend single bonds horizontally through the square brackets on each side to show open continuation bonds.
Add a subscript \(n\) outside the right bracket to represent a large number of repeating units.

The 4 Prescribed Addition Polymers:

1. Poly(ethene):
Monomer: Ethene (\(\text{CH}_2=\text{CH}_2\))
Polymer repeat unit: \(-[\text{CH}_2-\text{CH}_2]_n-\)

2. Poly(propene):
Monomer: Propene (\(\text{CH}_2=\text{CH}-\text{CH}_3\))
Polymer repeat unit: \(-[\text{CH}_2-\text{CH}(\text{CH}_3)]_n-\)

3. Poly(chloroethene) (PVC):
Monomer: Chloroethene (\(\text{CH}_2=\text{CHCl}\))
Polymer repeat unit: \(-[\text{CH}_2-\text{CH(Cl)}]_n-\)

4. Poly(tetrafluoroethene) (PTFE / Teflon):
Monomer: Tetrafluoroethene (\(\text{CF}_2=\text{CF}_2\))
Polymer repeat unit: \(-[\text{CF}_2-\text{CF}_2]_n-\)

Deducing Monomer from Repeat Unit and Vice Versa

Monomer to Repeat Unit: Change the \(\text{C}=\text{C}\) double bond to a \(\text{C}-\text{C}\) single bond, draw extension bonds extending out through brackets, and add \(n\).
Repeat Unit to Monomer: Identify the two-carbon backbone of the repeat unit, remove the extension bonds, remove the brackets and \(n\), and replace the single \(\text{C}-\text{C}\) bond with a \(\text{C}=\text{C}\) double bond.

3. Disposal Problems of Addition Polymers

While the durability and unreactive nature of synthetic addition polymers make them extremely useful, they cause significant environmental problems upon disposal:

Inertness and Non-biodegradability: Synthetic addition polymers contain strong carbon-carbon (\(\text{C}-\text{C}\)) single bonds and are chemically inert (unreactive). Microorganisms (bacteria and fungi) cannot readily break these bonds, meaning these plastics do not biodegrade. They remain intact in landfill sites and oceans for hundreds of years.
Toxic Gases on Incineration: Burning (incinerating) plastic waste reduces volume and releases energy, but it produces harmful pollutants. Complete combustion produces carbon dioxide (a greenhouse gas), incomplete combustion produces toxic carbon monoxide, and polymers containing other elements (such as chlorine in poly(chloroethene)) release toxic gases like hydrogen chloride (\(\text{HCl}\)) when burned.

4. Condensation Polymerisation (Paper 2 Only)

In condensation polymerisation, monomers with two functional groups react together to form a polymer chain, releasing a small molecule (such as water, \(\text{H}_2\text{O}\)) as a byproduct for each bond formed.

Making Polyesters

A polyester is formed by the reaction between:

A dicarboxylic acid (a molecule containing two \(-\text{COOH}\) carboxyl groups, \(\text{HOOC}-\text{R}_1-\text{COOH}\)).
A diol (a molecule containing two \(-\text{OH}\) alcohol groups, \(\text{HO}-\text{R}_2-\text{OH}\)).

Each \(-\text{COOH}\) group reacts with an \(-\text{OH}\) group to form an ester link (\(-\text{COO}-\)) with the elimination of a molecule of \(\text{H}_2\text{O}\).

General Word Equation:
\(\text{dicarboxylic acid} + \text{diol} \rightarrow \text{polyester} + \text{water}\)

Specific Example: Ethanedioic Acid with Ethanediol

Dicarboxylic acid monomer: Ethanedioic acid (\(\text{HOOC}-\text{COOH}\))
Diol monomer: Ethanediol (\(\text{HO}-\text{CH}_2-\text{CH}_2-\text{OH}\))

The repeat unit of this polyester is:
\(-[\text{O}-\text{CH}_2-\text{CH}_2-\text{O}-\text{CO}-\text{CO}]_n-\)
For \(n\) units of each monomer joining together, \(2n\) molecules of water (\(\text{H}_2\text{O}\)) are produced.

Biopolyesters: The Biodegradable Solution

Biopolyesters are synthetic polymers derived from renewable biological resources or engineered with ester linkages that can be broken down naturally by microorganisms over time.

Because they are biodegradable, they break down in the environment much faster than addition polymers, significantly reducing landfill waste and plastic pollution.

Chapter Summary Review

Key Takeaways:

Addition Polymerisation: Unsaturated monomers (alkenes) open their double bonds to form one single polymer product. Prescribed examples: poly(ethene), poly(propene), poly(chloroethene), and poly(tetrafluoroethene).
Disposal Issues: Addition polymers are inert and non-biodegradable; burning them releases toxic gases.
Condensation Polymerisation (P2): A dicarboxylic acid reacts with a diol to form a polyester and water (\(\text{H}_2\text{O}\)).
Biopolyesters (P2): Polyesters engineered to be biodegradable, offering a sustainable alternative to conventional plastics.

References

Pearson Edexcel International GCSE (9-1) Chemistry Specification — Pearson Edexcel

Quick check

Can you answer these now?

Open each question to check the key ideas from this chapter.

What is the difference between a monomer and a polymer?

A monomer is a small, simple molecule that acts as a single repeating unit, whereas a polymer is a large macromolecule formed when many monomers chemically join together.

What occurs during addition polymerisation?

Unsaturated monomers containing carbon-carbon double bonds ("> ext{C}= ext{C}<") open their double bonds to form a single long polymer chain of single bonds, producing no other byproduct.

How do you draw the repeat unit of an addition polymer from its monomer?

Replace the \(\text{C}=\text{C}\) double bond with a single \(\text{C}-\text{C}\) bond, keep attached groups in the same positions, and draw extension bonds extending horizontally through square brackets with a subscript \(n\).

What are the monomers and repeat units of the four prescribed addition polymers: poly(ethene), poly(propene), poly(chloroethene), and poly(tetrafluoroethene)?

Poly(ethene): \(\text{CH}_2=\text{CH}_2 \rightarrow -[\text{CH}_2-\text{CH}_2]_n-\); Poly(propene): \(\text{CH}_2=\text{CH}-\text{CH}_3 \rightarrow -[\text{CH}_2-\text{CH}(\text{CH}_3)]_n-\); Poly(chloroethene): \(\text{CH}_2=\text{CHCl} \rightarrow -[\text{CH}_2-\text{CH(Cl)}]_n-\); Poly(tetrafluoroethene): \(\text{CF}_2=\text{CF}_2 \rightarrow -[\text{CF}_2-\text{CF}_2]_n-\).

How can you deduce the monomer from a given addition polymer repeat unit?

Identify the two-carbon backbone of the repeat unit, remove the extension bonds and brackets, and replace the single \(\text{C}-\text{C}\) bond with a \(\text{C}=\text{C}\) double bond.

Why are addition polymers non-biodegradable and difficult to dispose of in landfills?

Addition polymers are chemically inert because of their strong, unreactive \(\text{C}-\text{C}\) single bonds, meaning microorganisms cannot break them down naturally.

What environmental problems are associated with the incineration of synthetic addition polymers?

Incineration produces carbon dioxide (a greenhouse gas), toxic carbon monoxide from incomplete combustion, and hazardous acidic gases such as hydrogen chloride (\(\text{HCl}\)) from chlorine-containing polymers like PVC.

What is condensation polymerisation?

Condensation polymerisation is a reaction where monomers with two functional groups combine to form a polymer chain, eliminating a small molecule such as water (\(\text{H}_2\text{O}\)) at each linkage.

Which two types of monomers react to form a polyester, and what linkage connects them?

A dicarboxylic acid (containing two \(-\text{COOH}\) groups) and a diol (containing two \(-\text{OH}\) groups) react to form ester linkages (\(-\text{COO}-\)) and water.

What is the repeat unit formed from the condensation polymerisation of ethanedioic acid and ethanediol?

The repeat unit is \(-[\text{O}-\text{CH}_2-\text{CH}_2-\text{O}-\text{CO}-\text{CO}]_n-\), producing \(2n\) molecules of \(\text{H}_2\text{O}\) as a byproduct.

What are biopolyesters and why are they environmentally advantageous?

Biopolyesters are biodegradable polyesters derived from renewable biological resources or engineered so that microorganisms can break down their ester links naturally.

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