Anionic addition polymerization: Difference between revisions

Revision as of 14:51, 30 September 2019

Revision as of 17:09, 30 September 2019

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== Initiation ==

Initiators is selected based on the reactivity of the monomers. Highly electrophilic monomers such as cyanoacrylates require only weakly nucleophilic initiators, such as amines, phosphines, or even halides. Less reactive monomers such as styrene require powerful nucleophiles such as [[butyl lithium]]. Reaction of intermediate strength are used for monomers of intermediate reactivity such as [[vinylpyridine]].<ref name="Quirk"/>

The solvent used in anionic addition polymerizations are determined by the reactivity of both the initiator and nature of the propagating chain end. Anionic species with low reactivity, such as [[heterocyclic]] monomers, can use a wide range of solvents.<ref name="Quirk"/>

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===Initiation by strong anions===

[[Nucleophilic]] initiators include covalent or ionic metal [[amide]]s, [[alkoxide]]s, [[hydroxide]]s, [[cyanide]]s, [[phosphine]]s, [[amine]]s and organometallic compounds ([[alkyllithium]] compounds and [[Grignard reagents]]). The initiation process involves the addition of a neutral (B:) or negative (B:-) [[nucleophile]] to the monomer.<ref name=Odian/>

The most commercially useful of these initiators has been the [[alkyllithium]] initiators. They are primarily used for the polymerization of styrenes and dienes.<ref name="Quirk"/>

Monomers activated by strong electronegative groups may be initiated even by weak anionic or neutral [[nucleophiles]] (i.e. amines, phosphines). Most prominent example is the curing of [[cyanoacrylate]], which constitutes the basis for [[superglue]]. Here, only traces of basic impurities are sufficient to induce an anionic addition polymerization or [[zwitterionic addition polymerization]], respectively.<ref>Pepper, D.C. Zwitterionic Chain Polymerizations of Cyanoacrylates. ''Macromolecular Symposia''; '''1992''',''60'',pp. 267-277. [http://onlinelibrary.wiley.com/doi/10.1002/masy.19920600124/abstract]</ref>

== Propagation ==