##  [Free-Radical Polymerization](/free-radical-polymerization-0) 

 Definition

A chain-growth polymerization mechanism initiated by free radicals in which monomer molecules add sequentially to a radical chain end. The cycle proceeds through distinct initiation, radical propagation, chain transfer, and termination steps and typically yields polymers with broad molecular-weight distributions unless additional control methods are employed.

 

 

 

 

 

 





## Principle

Principle

Radical centers (unpaired-electron species) add to unsaturated monomers to form a new radical at the chain terminus; the balance between propagation, chain-transfer, and termination events determines chain length and dispersity.

 

 

 

 

 





## Demonstration

Demonstration

Polymerization of styrene initiated thermally by a peroxide or azo initiator: an initiator decomposes to radicals, a radical adds to styrene producing a phenethyl radical, repeated additions produce polystyrene chains until termination by recombination or disproportionation.

 

 

 

 

## Misapplication

Misapplication

Treating free-radical polymerization as if it were step-growth (where all chains grow gradually by bimolecular combination) or assuming that monomer conversion alone controls molecular weight without accounting for transfer and termination events.

 

 

 

 

 





## Consequence

Consequence

Rapid chain growth enabling high polymerization rates and synthesis of a wide range of vinyl polymers; observable consequences include sensitivity to oxygen, radicals’ reactivity determining tacticity and chain defects, and typically high dispersity unless mediated.

 

 

 

 

## Reversal

Reversal

Replacing the process with a living/controlled radical method (e.g., reversible-deactivation radical polymerization) or with ionic polymerization inverts control over chain-ends and often yields narrower molecular-weight distributions and different end-group chemistry.

 

 

 

 

 





## Boundary

Boundary

Applies to chain-growth mechanisms propagated by free radicals acting at a carbon-centered (or heteroatom-centered) radical site; excludes purely ionic, condensation (step-growth) polymerizations and specific reversible-deactivation variants unless explicitly specified.

 

 

 

 

 





## Semantic Tension

Semantic Tension

Distinguishing ‘free-radical polymerization’ from broadly ‘radical polymerization’ or from ‘controlled/living radical’ methods—terms overlap in everyday use but differ in mechanistic detail and in expectations for molecular-weight control.

 

 

 

 

 





## Synthesis

Synthesis

A rapid chain-growth process driven by reactive radical chain ends that repeatedly add monomer; the final polymer properties reflect the competition between propagation, transfer, and termination, and modest control of molecular weight requires additional reversible-deactivation strategies.