Chain-growth polymerization or chain polymerization is a polymerization technique in which unsaturated monomer molecules add onto the active site of a growing polymer chain one at a time. Addition of each monomer unit regenerates the active site. They are the primary component of four of the plastics specifically labeled addition and condensation polymerization pdf recycling codes and are used extensively in packaging. This type of polymerization result in high molecular weight polymer being formed at low conversion.
This final weight is determined by the rate of propagation compared to the rate of individual chain termination, which includes both chain transfer and chain termination steps. Above a certain ceiling temperature, no polymerization occurs. Typical initiators include organic compounds with a labile group: e.
Two examples are benzoyl peroxide and AIBN. This can occur by reaction with the solvent, monomer, or another polymer molecule. Reaction with another polymer molecule results in the formation of a branched polymer.
Termination, in radical polymerization, is when the free radicals combine and is the end of the polymerization process. Under the necessary reaction conditions, an addition polymerization can be considered a living polymerization. This is most often seen with anionic polymerization as it can be easy to perform without termination steps.
The distinction between step-growth polymerization and chain-growth polymerization was introduced by Paul Flory in 1953, and refers to the difference in reaction mechanisms with step-growth using the functional groups of the monomer compared to the free-radical or ion groups used in chain-growth polymerization. The distinction between “addition polymerization” and “condensation polymerization” was introduced by Wallace Hume Carothers in 1929, and refers to the type of product produced. Addition polymerization produces only a polymer molecule, while condensation polymerization produces a polymer as well as a molecule with a low molecular weight, usually water. Introduction to Polymers 1987 R.