Anionic addition polymerization: Difference between revisions

Revision as of 11:53, 26 August 2019

Revision as of 13:54, 26 August 2019

Line 18:

== History ==

[[File:ET-coupledStyrene.png|thumb|Product of the reductive coupling of styrene, 1,4-dilithio-1,4-diphenylbutane.<ref>{{cite book|chapter=Ionic Polymerization|author=Sebastian Koltzenburg, Michael Maskos, Oskar Nuyken|title=Polymer Chemistry|isbn=978-3-662-49279-6|publisher=Springer}}</ref>]]

As early as 1936, [[Karl Ziegler]] proposed that anionic polymerization of styrene and butadiene by consecutive addition of monomer to an alkyl lithium initiator occurred without chain transfer or termination. Twenty years later, living polymerization was demonstrated by Szwarc.<ref>{{cite journal|author=M. Szwarc |year=1956|title="Living" polymers|journal=Nature|volume=178|page=1168|doi=10.1038/1781168a0}}</ref> The early work of [[Michael Szwarc]] and co – workers in 1956 was In one of the breakthrough events in the field of [[polymer science]]. When, Szwarc learned that the [[electron transfer]] between [[radical anion]] of [[naphthalene]] and [[styrene]] in an [[aprotic solvent]] such as [[tetrahydrofuran]] gave a messy product, he started investigating the reaction in more detail. He proved that the electron transfer results in the formation of a [[dianion]], which rapidly added styrene to form a "two – ended living polymer." Being a [[physical chemist]], Szwarc set forth in understanding the mechanism of such living polymerization in greater detail. His work elucidated the [[chemical kinetics|kinetics]] and the [[thermodynamics]] of the process in considerable detail. At the same time, he explored the structure property relationship of the various [[ion pair]]s and radical ions involved. This hadwork greatprovided ramificationsthe infoundations futurefor researchthe in polymerrational synthesis, because Szwarc had found a way to makeof polymers with greater control over [[molecular weight]], molecular weight distribution, and the architecture of the polymer.<ref>Smid, J. Historical Perspectives on Living Anionic Polymerization. ''J. Polym. Sci. Part A.''; '''2002''', ''40'',pp. 2101-2107. [https://archive.today/20121012113202/http://www3.interscience.wiley.com/journal/94515609/abstract DOI=10.1002/pola.10286]</ref>

The use of [[alkali metals]] to initiate polymerization of 1,3-[[diene]]s led to the discovery by Stavely and co-workers at Firestone Tire and Rubber company of cis-1,4-[[polyisoprene]].<ref name=Odian>Odian, G. Ionic Chain Polymerization; In '' Principles of Polymerization''; Wiley-Interscience: Staten Island, New York, 2004, pp. 372-463.</ref> This sparked the development of commercial anionic polymerization processes that utilize alkyllithium initiatiors.<ref name="Quirk"/>

Line 44 ⟶ 45:

Initiation of styrene polymerization with sodium naphthalene proceeds by [[electron transfer]] from the [[naphthalene]] radical anion to the monomer. The resulting radical dimerizes to give a dilithio compound, which then functions as the initiator. Polar solvents are necessary for this type of initiation both for stability of the anion-radical and to solvate the cation species formed.<ref name=Odian/> The anion-radical can then transfer an electron to the monomer.

Initiation can also involve the transfer of an electron from the alkali metal to the monomer to form an anion-radical. Initiation occurs on the surface of the metal, with the reversible transfer of an electron to the adsorbed monomer.<ref name="Quirk"/>

[[File:ET-coupledStyrene.png|thumb|Product of the reductive coupling of styrene, 1,4-dilithio-1,4-diphenylbutane.<ref>{{cite book|chapter=Ionic Polymerization|author=Sebastian Koltzenburg, Michael Maskos, Oskar Nuyken|title=Polymer Chemistry|isbn=978-3-662-49279-6|publisher=Springer}}</ref>]]

===Initiation by strong anions===