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Living polymerization
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==History== Living polymerization was demonstrated by [[Michael Szwarc]] in 1956 in the anionic polymerization of [[styrene]] with an [[alkali metal]] / [[naphthalene]] system in [[tetrahydrofuran]] (THF). Szwarc showed that [[electron transfer]] occurred from [[radical anion]] of [[naphthalene]] to [[styrene]]. The initial radical anion of styrene converts to a [[dianion]] (or equivalently disodio-) species, which rapidly added styrene to form a "two β ended living polymer." An important aspect of his work, Szwarc employed the [[aprotic solvent]] [[tetrahydrofuran]], which dissolves but is otherwise unreactive toward the organometallic intermediates. After initial addition of monomer to the initiator system, the [[viscosity]] increased (due to increased polymer chain growth), but eventually cease after depletion of monomer concentration. However, he found that addition of ''more'' monomer caused an increase in viscosity, indicating growth of the polymer chain, and thus concluded that the polymer chains had never been terminated.<ref name="ReferenceA">{{Cite journal | doi = 10.1021/ja01592a101| title = Polymerization Initiated by Electron Transfer to Monomer. A New Method of Formation of Block Polymers1| journal = Journal of the American Chemical Society| volume = 78| issue = 11| pages = 2656β2657| year = 1956| last1 = Szwarc | first1 = M.| last2 = Levy | first2 = M.| last3 = Milkovich | first3 = R.}}</ref> This was a major step in polymer chemistry, since control over when the polymer was quenched, or terminated, was generally not a controlled step. With this discovery, the list of potential applications expanded dramatically.<ref>{{cite journal|author=M. Szwarc |year=1956|title="Living" polymers|journal=Nature|volume=178|issue=4543|page=1168|doi=10.1038/1781168a0}}</ref> Today, living polymerizations are used widely in the production of many types of polymers or plastics. For instance, [[poly(phthalaldehyde)]] polymer, first developed in 1967, can be synthesized via both [[Living cationic polymerization|living cationic]] and [[Living anionic polymerization|living anionic]] polymerization reactions producing both the cyclic or linear form of the polymer respectively. The approach offers control of the chemical makeup of the polymer and, thus, the structural and electronic properties of the material. This level of control rarely exists in non-living polymerization reactions.<ref name=Principles /><ref name="McNeil 1" />
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