Chem 421: Introduction to Polymer Chemistry

Free Radical Polymerization - Initiation

Thermal initiators:

• Most common kind of FR initiator.
• Unimolecular decomposition.
• First order kinetics.
• Most common examples: peroxides or azo compounds.

Peroxides:

Azo compounds:

(Temperatures are for 10 hour half-lives.)

Redox initiators:

• Usually 2 component.
• Rarely used.
• Example: Fenton's reagent

Self-initiation:

• Only proven to occur with styrene.
• Mechanism involves preliminary dimer formation (via Diels-Alder reaction of two monomers, followed by hydrogen atom transfer to a third monomer).

Photochemical:

• One or two component.
• Used for thin films.
• Examples:

Ionizing radiation:

• X-ray, gamma-ray.
• Random destruction leads to radical formation.
• Used only in very special cases.

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