Polymers and Macromolecules
Understand how small monomer units join to form large polymer chains through addition and condensation reactions, and explore their properties and applications.
Monomers and Polymers
A polymer is a large molecule (macromolecule) made up of many repeating smaller units called monomers. The process of joining monomers together is called polymerisation.
Monomer to Polymer
Many small monomers join to form a long polymer chain
Naming convention: Polymers are typically named by adding "poly-" to the monomer name. For example, ethene monomers form polyethene (polyethylene), and styrene forms polystyrene.
Addition vs Condensation Polymerisation
There are two main types of polymerisation. They differ in how monomers join and whether a small molecule is released.
Addition Polymerisation
- • Monomers have a C=C double bond
- • Double bond opens up and monomers link
- • No by-product is released
- • All atoms from monomers end up in the polymer
- • Examples: polyethene, polypropylene, PVC, polystyrene
Condensation Polymerisation
- • Monomers have two functional groups
- • Functional groups react to link monomers
- • A small molecule (usually water) is released
- • Polymer has fewer atoms than the combined monomers
- • Examples: nylon, polyester, proteins, starch
Key difference: Addition polymerisation produces no by-product, while condensation polymerisation releases a small molecule (such as H2O or HCl) for each new bond formed.
Properties and Applications
The properties of a polymer depend on its structure: the type of monomer, chain length, branching, and cross-linking. These properties determine how the polymer is used.
Common Polymers and Their Uses
Polyethene (PE)
Flexible, chemically resistant. Used in plastic bags, bottles, and packaging.
PVC (Polyvinyl Chloride)
Rigid or flexible with plasticisers. Used in pipes, flooring, and cable insulation.
Nylon (Polyamide)
Strong, elastic, resistant to wear. Used in textiles, ropes, and gears.
Polyester (PET)
Strong, wrinkle-resistant. Used in clothing, drink bottles, and food packaging.
Environmental Considerations
• Non-biodegradable: Most synthetic polymers (especially addition polymers) do not break down easily, causing pollution.
• Recycling: Thermoplastics can be melted and reshaped; thermosets cannot be recycled easily.
• Bioplastics: New polymers from renewable sources (e.g., PLA from corn starch) are being developed as sustainable alternatives.
Key Vocabulary
Monomer
A small, reactive molecule that can join with others to form a polymer chain.
Polymer
A large molecule (macromolecule) composed of many repeating monomer units linked by covalent bonds.
Addition Polymerisation
A reaction where unsaturated monomers join by opening their double bonds, with no by-product formed.
Condensation Polymerisation
A reaction where monomers with two functional groups link together, releasing a small molecule (often water) each time.
Worked Examples
Identify the type of polymerisation used to make polyethene from ethene (CH2=CH2).
Step 1: Ethene contains a C=C double bond.
Step 2: During polymerisation, the double bond opens and monomers link in a chain.
Step 3: No small molecule is released. This is addition polymerisation.
Explain why nylon is made by condensation polymerisation.
Step 1: Nylon is formed from two types of monomers: a diamine (two -NH2 groups) and a dicarboxylic acid (two -COOH groups).
Step 2: When -NH2 reacts with -COOH, an amide bond (-CONH-) forms and a water molecule is released.
Step 3: Because a small molecule (H2O) is produced with each link, this is condensation polymerisation.
Explain why most addition polymers are non-biodegradable.
Step 1: Addition polymers have a carbon backbone made entirely of strong C-C single bonds.
Step 2: These bonds are chemically very stable and resistant to attack by microorganisms and enzymes.
Step 3: Unlike condensation polymers (which can be hydrolysed), the C-C backbone does not break down easily in the environment, making them non-biodegradable.
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
Which feature must a monomer have to undergo addition polymerisation?
Question 2
What small molecule is typically released during condensation polymerisation?
Question 3
Which of the following is a condensation polymer?
Question 4
Why are most addition polymers difficult to recycle by chemical means?
Question 5
Which biological macromolecule is formed by condensation polymerisation of amino acids?
Key Concepts Summary
- ●Polymers are large molecules made of repeating monomer units.
- ●Addition polymerisation requires C=C double bonds and produces no by-product.
- ●Condensation polymerisation uses bifunctional monomers and releases a small molecule (e.g. water).
- ●Polymer properties depend on monomer type, chain length, branching, and cross-linking.
- ●Most synthetic addition polymers are non-biodegradable, raising environmental concerns.