Polymers
Polymers are long chains of repeating units called monomers. They are made when lots of small molecules join together in a process called polymerisation.
What is a polymer?
A polymer is a large molecule made from lots of smaller molecules (monomers) that are chemically bonded together.
- The monomers are usually alkenes (contain a C=C double bond)
- When they join together, they form a long repeating chain
- The double bond breaks and forms single bonds to link the monomers
What is polymerisation?
Polymerisation is the chemical reaction that joins many monomers into a polymer.
- It is usually done under high pressure and with catalysts
- The type of polymer formed depends on the monomer used
Example:
- Monomer: ethene (C₂H₄)
- Polymer: poly(ethene)
Structure of a polymer
- Show the repeating unit of poly(ethene) with square brackets and ‘n’ to represent many units
Repeating unit = a section of the polymer that shows how the monomers are joined together
Natural vs. synthetic polymers
Type | Examples |
Natural | DNA, proteins, starch, cellulose |
Synthetic | Poly(ethene), poly(propene), nylon |
Properties of polymers
Property | Explanation |
Solid at room temperature | Strong bonds between monomers give strength |
Flexible | Chains can bend and stretch |
Insoluble in water | Most synthetic polymers don’t dissolve easily |
Variable melting points | Depends on the type of polymer and how cross-linked or branched it is |
Uses of polymers
- Plastic bags – poly(ethene)
- Food containers – poly(propene)
- Clothing fibres – polyester, nylon
- Medical and industrial – hydrogels, biopolymers, biodegradable plastics
Questions
- What is a polymer made from?
- What is the name of the reaction that forms a polymer?
- What is the monomer of poly(ethene)?
- Is DNA a natural or synthetic polymer?
- Why are polymers flexible?
Summary
- Polymers are long-chain molecules made from repeating units (monomers)
- Polymerisation is the reaction that joins monomers together
- Alkenes are common monomers used in making addition polymers
- Polymers can be natural (like DNA) or synthetic (like plastics)
- Their properties vary depending on the structure, but most are solid, flexible, and strong