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Vinyl monomers have the formula CH<sub>2</sub>=CHR, the most important are styrene (R = C<sub>6</sub>H<sub>5</sub>), butadiene (CH=CH<sub>2</sub>), and isoprene (R = C(Me)=CH<sub>2</sub>). A second major class of monomers are acrylate esters, such as [[acrylonitrile]], [[methacrylate]], [[cyanoacrylate]], and [[acrolein]]. Other vinyl monomers include [[vinylpyridine]], vinyl [[sulfone]], vinyl [[sulfoxide]], [[vinyl silane]]s.<ref name="Quirk"/>
[[Image:Ex polar monomers.png|thumb|300px|center|Examples of polar monomers.]]
[[Image:Example Vinyl monomer.png|thumb|200px|left|Examples of vinyl monomers.]]▼
===Cyclic monomers===
[[file:Hexamethylcyclotrisiloxan.svg|thumb|140px|left|Hexamethylcyclotrisiloxane]] is a cyclic monomer that is susceptible to anionic polymerization to [[siloxane]] polymers.]]
Many cyclic compounds are susceptible to [[ring-opening polymerization]]. [[Epoxide]]s, cyclic tri[[siloxane]]s, some lactones, [[lactide]]s, [[cyclic carbonate]]s, and [[amino acid N-carboxyanhydride]]s.
In order for polymerization to occur with [[vinyl group|vinyl]] [[monomer]]s, the [[substituent]]s on the [[double bond]] must be able to stabilize a [[negative charge]]. Stabilization occurs through [[delocalization]] of the negative charge. Because of the nature of the [[carbanion]] propagating center, substituents that react with bases or nucleophiles either must not be present or be protected.<ref name="Quirk"/>
▲[[Image:Example Vinyl monomer.png|thumb|200px|left|Examples of vinyl monomers.]]
== Initiation ==
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