Editing Polymerization (section)

===Chain-growth===
{{Main|Chain-growth polymerization}}
In chain-growth (or chain) polymerization, the only chain-extension reaction step is the addition of a monomer to a growing chain with an active center such as a [[free radical]], [[cation]], or [[anion]]. Once the growth of a chain is initiated by formation of an active center, chain propagation is usually rapid by addition of a sequence of monomers. Long chains are formed from the beginning of the reaction.<ref name=":0" /><ref name=":1" />

Chain-growth polymerization (or addition polymerization) involves the linking together of unsaturated monomers, especially containing carbon-carbon [[double bonds]]. The pi-bond is lost by formation of a new sigma bond. Chain-growth polymerization is involved in the manufacture of polymers such as [[polyethylene]], [[polypropylene]], [[polyvinyl chloride]] (PVC), and [[acrylate]]. In these cases, the alkenes RCH=CH<sub>2</sub> are converted to high molecular weight alkanes (-RCHCH<sub>2</sub>-)<sub>n</sub>  (R = H, CH<sub>3</sub>, Cl, CO<sub>2</sub>CH<sub>3</sub>).

Other forms of chain growth polymerization include [[cationic addition polymerization]] and [[anionic addition polymerization]]. A special case of chain-growth polymerization leads to [[living polymerization]]. [[Ziegler–Natta polymerization]] allows considerable control of [[Branching (polymer chemistry)|polymer branching]].

[[File:Ethylene polymerization.png|thumb|right|Polymerization of [[ethylene]]]]

Diverse methods are employed to manipulate the initiation, propagation, and termination rates during chain polymerization. A related issue is [[temperature control]], also called heat management, during these reactions, which are often highly exothermic. For example, for the polymerization of ethylene, 93.6 kJ of energy are released per mole of monomer.<ref name=ullmannC2/>

The manner in which polymerization is conducted is a highly evolved technology.  Methods include [[emulsion polymerization]], [[solution polymerization]], [[suspension polymerization]], and [[precipitation polymerization]]. Although the polymer [[dispersity]] and molecular weight may be improved, these methods may introduce additional processing requirements to isolate the product from a solvent.