Difference Between Chain Growth and Additional Polymerization
Chain growth and additional polymerization are crucial mechanisms in polymer chemistry, each with distinct characteristics and processes.
Chain Growth Polymerization
- Definition: A method where monomers with unsaturated bonds (like alkenes) link together to form a polymer.
- Mechanism:
- Initiation: A reactive species (initiator) generates free radicals.
- Propagation: Free radicals react with monomers, creating new radicals that continue to react.
- Termination: The process stops when two radicals combine or a radical is quenched.
- Characteristics:
- Rapid growth of polymer chains.
- Typically produces high molecular weight polymers.
- Examples include polyethylene and polystyrene.
Additional Polymerization
- Definition: A type of polymerization where monomers add to each other without the loss of any small molecules.
- Mechanism:
- Stepwise addition of monomers, which often contain functional groups.
- Can involve condensation reactions where by-products (like water) may form.
- Characteristics:
- Generally involves more complex monomers.
- Products can have varying molecular weights, leading to a mix of polymer sizes.
- Examples include polyesters and polyamides.
Key Differences
- Process Type: Chain growth is a rapid sequential process; additional polymerization may involve stepwise reactions.
- Molecular Structure: Chain growth typically yields higher molecular weight polymers, while additional polymerization can result in a distribution of molecular weights.
- By-products: Chain growth does not create by-products, whereas additional polymerization may release small molecules.
Understanding these differences is essential for selecting the appropriate polymerization method for specific applications in materials science.