IntermediateTopic 39 of 100Materials & Chemical
Polymerisation
Chain-growth and step-growth reactions build polymers.
In depth
Chain-growth (addition: initiation, propagation, termination) makes polyethylene, PVC, polystyrene; step-growth (condensation) makes polyesters, nylons, polyurethanes, epoxies. Molecular weight distribution and branching govern properties; copolymers and blends tailor behaviour.
Key points
- Free radical and Ziegler-Natta catalysts
- Mn and Mw
- Crosslinking
ExamplePET forms by condensation of terephthalic acid and ethylene glycol.
What is Polymerisation?
Chain-growth and step-growth reactions build polymers.
Why is it important to understand polymerisation?
Polymerisation determines the structure and properties of plastics, since chain length and branching control strength and processability.
What is chain-growth polymerisation?
Monomers add one by one to a growing chain that starts from an active site, as in the production of polyethylene.
What is step-growth polymerisation?
Monomers react with each other to form dimers, trimers and longer chains, as in nylon and polyester production.
How is Polymerisation used in practice?
Typical applications include choosing a grade of polyethylene for a flexible film or a rigid tank, controlling molecular weight to get the right toughness for an injection-moulded part and understanding why some plastics are branched and others linear.
What should I learn before Polymerisation?
Study "Polymers" first (topic 38 of 100 in Materials & Chemical). It covers the groundwork this topic builds on.
What are the key points of Polymerisation?
Free radical and Ziegler-Natta catalysts. Mn and Mw. Crosslinking.
Can you give an example of Polymerisation?
PET forms by condensation of terephthalic acid and ethylene glycol.
What comes after Polymerisation?
The next topic is "Thermoplastics", which builds directly on this one.
How difficult is Polymerisation?
It is classed as Intermediate in Materials & Chemical (topic 39 of 100). It is an intermediate topic. Work through the beginner topics in Materials & Chemical first.