Addition and Condensation Polymers

This lesson covers polymers — both addition and condensation types — as required by the Edexcel GCSE Chemistry specification (1CH0). You need to understand how polymers are formed, be able to draw sections of addition polymers from monomers (and vice versa), know about condensation polymerisation and natural polymers, and appreciate the environmental issues associated with polymer waste.

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What Are Polymers?

A polymer is a very large molecule (macromolecule) made by joining together many small molecules called monomers. The process of making a polymer is called polymerisation.

Term	Definition
Monomer	A small molecule that can join with others to form a polymer
Polymer	A very large molecule made from many repeating monomer units
Polymerisation	The chemical reaction in which monomers join together to form a polymer

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Addition Polymerisation

How It Works

Addition polymerisation occurs when many alkene monomers (each containing a C=C double bond) join together. The double bond in each monomer opens up, and the monomers link together to form a long chain with only single C–C bonds.

Key features of addition polymerisation:

• The monomer must contain a C=C double bond (it must be an alkene or a substituted alkene).
• The double bond opens to form two new single bonds — one to the monomer on the left, one to the monomer on the right.
• No other molecule is produced — the only product is the polymer.
• The polymer has the same atoms as the monomers, just bonded differently.

Drawing Addition Polymers

From monomer to polymer:

To draw a section of an addition polymer from its monomer:

1. Draw the monomer and identify the C=C double bond.
2. Open the double bond to make a single bond: C–C.
3. Add extension bonds at each end (showing the chain continues).
4. Enclose the repeating unit in square brackets with an n subscript.

From polymer to monomer:

To identify the monomer from a section of addition polymer:

1. Identify the repeating unit (the pattern that repeats).
2. Write the repeating unit with a C=C double bond (close the two extension bonds into a double bond).

Common Addition Polymers

Monomer	Monomer formula	Polymer	Polymer formula	Uses
Ethene	CH₂=CH₂	Poly(ethene) / polyethylene	–(CH₂–CH₂)ₙ–	Plastic bags, bottles, cling film
Propene	CH₂=CHCH₃	Poly(propene) / polypropylene	–(CH₂–CHCH₃)ₙ–	Rope, crates, car bumpers
Chloroethene (vinyl chloride)	CH₂=CHCl	Poly(chloroethene) / PVC	–(CH₂–CHCl)ₙ–	Window frames, pipes, flooring
Tetrafluoroethene	CF₂=CF₂	PTFE (Teflon)	–(CF₂–CF₂)ₙ–	Non-stick pans, waterproof coatings

Exam Tip: The polymer is named poly(monomer name). For example, the polymer made from ethene is poly(ethene); from propene it is poly(propene). The prefix "poly-" means "many".

Worked Example

Monomer: Ethene, CH₂=CH₂

Step 1: Open the double bond → –CH₂–CH₂–

Step 2: Show the repeating unit in brackets:

Polymer: –[CH₂–CH₂]ₙ– (where n is a very large number, typically thousands)

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Condensation Polymerisation

How It Works

Condensation polymerisation occurs when two different types of monomer join together, and a small molecule is released (eliminated) each time a bond forms. The small molecule is usually water (H₂O), though it can sometimes be HCl or another small molecule.

Key features of condensation polymerisation:

• Two different monomers are needed, each with functional groups at both ends.
• A small molecule (usually water) is released at each link.
• The polymer chain builds up by alternating the two monomer types.

Comparison: Addition vs Condensation

Feature	Addition polymerisation	Condensation polymerisation
Number of monomer types	One	Usually two different monomers
Monomer requirement	Must contain C=C double bond	Must have functional groups at both ends
Small molecule produced?	No	Yes (usually water)
Example	Poly(ethene) from ethene	Polyester from a diol + dicarboxylic acid

Exam Tip: The key distinction is: addition polymerisation produces only the polymer; condensation polymerisation produces the polymer plus a small molecule (usually water).

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Natural Polymers

Polymers are not only synthetic (man-made) — many occur naturally in living organisms. These are all formed by condensation polymerisation.

Natural polymer	Monomer	Where found	Function
Proteins	Amino acids	All living organisms	Enzymes, structural components, antibodies, hormones
DNA	Nucleotides	Cell nuclei	Stores genetic information
Starch	Glucose (α-glucose)	Plants	Energy storage
Cellulose	Glucose (β-glucose)	Plant cell walls	Structural support
Glycogen	Glucose	Animals (liver, muscles)	Energy storage

How Natural Condensation Polymers Form

When amino acids join together to make a protein:

• The amino group (–NH₂) of one amino acid reacts with the carboxyl group (–COOH) of the next.
• A peptide bond forms and a molecule of water (H₂O) is released.
• This is repeated many times to build up a long polypeptide chain.

Similarly, when glucose monomers join to form starch or cellulose, a molecule of water is released at each link (a glycosidic bond forms).

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Problems with Polymer Waste

Most synthetic polymers (plastics) are non-biodegradable — they are not broken down by microorganisms in the environment. This creates significant environmental problems.

Disposal Methods and Their Issues