View source for Chemistry:Copper(0)-mediated reversible-deactivation radical polymerization

<!--- Don't mess with this line! ---><!--- Write your article below this line --->
'''Copper(0)-mediated reversible-deactivation radical polymerization''' '''(Cu(0)-mediated RDRP)''' is a member of the class of [[Chemistry:Reversible-deactivation radical polymerization|reversible-deactivation radical polymerization]].<ref>{{cite journal|last1=Jenkins|first1=Aubrey D.|last2=Jones|first2=Richard G.|last3=Moad|first3=Graeme|title=Terminology for reversible-deactivation radical polymerization previously called "controlled" radical or "living" radical polymerization (IUPAC Recommendations 2010)|journal=Pure and Applied Chemistry|date=18 January 2009|volume=82|issue=2|pages=483–491|doi=10.1351/PAC-REP-08-04-03|s2cid=98243937|doi-access=free}}</ref> As the name implies, metallic [[Chemistry:Copper|copper]] is employed as the transition-metal catalyst for reversible activation/deactivation of the propagating chains responsible for uniform polymer chain growth.

==History of Copper-mediated RDRP== 
Although copper complexes (in combination with relevant ligands) have long been used as catalysts for organic reactions such as atom transfer radical addition (ATRA) and copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC), copper complex catalyzed RDRP was not reported until 1995 when Jin-Shan Wang and Krzysztof Matyjaszewski introduced it as atom transfer radical polymerization (ATRP).<ref>{{cite journal|last1=Wang|first1=Jin-Shan|last2=Matyjaszewski|first2=Krzysztof|title=Controlled/"living" radical polymerization. atom transfer radical polymerization in the presence of transition-metal complexes|journal=Journal of the American Chemical Society|date=May 1995|volume=117|issue=20|pages=5614–5615|doi=10.1021/ja00125a035}}</ref><ref>{{cite journal|last1=Kato|first1=Mitsuru|last2=Kamigaito|first2=Masami|last3=Sawamoto|first3=Mitsuo|last4=Higashimura|first4=Toshinobu|title=Polymerization of Methyl Methacrylate with the Carbon Tetrachloride/Dichlorotris- (triphenylphosphine)ruthenium(II)/Methylaluminum Bis(2,6-di-tert-butylphenoxide) Initiating System: Possibility of Living Radical Polymerization|journal=Macromolecules|date=September 1995|volume=28|issue=5|pages=1721–1723|doi=10.1021/ma00109a056|bibcode=1995MaMol..28.1721K}}</ref> ATRP with copper as catalyst quickly became one of the most robust and commonly used RDRP techniques for designing and synthesizing polymers with well-defined composition, functionalities, and architecture. Due to some inherited drawbacks, such the [[Chemistry:Persistent radical effect|persistent radical effect]] (PRE),<ref>{{cite journal|last1=Fischer|first1=Hanns|title=The Persistent Radical Effect: A Principle for Selective Radical Reactions and Living Radical Polymerizations|journal=Chemical Reviews|date=December 2001|volume=101|issue=12|pages=3581–3610|doi=10.1021/cr990124y|pmid=11740916}}</ref> several advanced ATRP techniques have been developed, including activators regenerated by electron transfer (ARGET) ATRP<ref>{{cite journal|last1=Jakubowski|first1=Wojciech|last2=Matyjaszewski|first2=Krzysztof|title=Activators Regenerated by Electron Transfer for Atom-Transfer Radical Polymerization of (Meth)acrylates and Related Block Copolymers|journal=Angewandte Chemie International Edition|date=3 July 2006|volume=45|issue=27|pages=4482–4486|doi=10.1002/anie.200600272|pmid=16770821|doi-access=free}}</ref> and initiators for continuous activator regeneration (ICAR) ATRP.<ref>{{cite journal|last1=Matyjaszewski|first1=K.|last2=Jakubowski|first2=W.|last3=Min|first3=K.|last4=Tang|first4=W.|last5=Huang|first5=J.|last6=Braunecker|first6=W. A.|last7=Tsarevsky|first7=N. V.|title=Diminishing catalyst concentration in atom transfer radical polymerization with reducing agents|journal=Proceedings of the National Academy of Sciences|date=10 October 2006|volume=103|issue=42|pages=15309–15314|doi=10.1073/pnas.0602675103|pmid=17032773|pmc=1622823|bibcode=2006PNAS..10315309M|doi-access=free}}</ref>

One intriguing catalyst, metallic copper, has also been applied to these modified ATRP systems. The polymerization using Cu(0) and suitable ligands was introduced for the first time by Krzysztof Matyjaszewski in 1997.<ref>{{cite journal|last1=Matyjaszewski|first1=Krzysztof|last2=Coca|first2=Simion|last3=Gaynor|first3=Scott G.|last4=Wei|first4=Mingli|last5=Woodworth|first5=Brian E.|title=Zerovalent Metals in Controlled/"Living" Radical Polymerization|journal=Macromolecules|date=November 1997|volume=30|issue=23|pages=7348–7350|doi=10.1021/ma971258l|bibcode=1997MaMol..30.7348M}}</ref> However, then, in 2006, the Cu(0) – mediated RDRP of MA (in combination with tris(2-(dimethylamino)ethyl)amine(Me6TREN) as ligand in polar solvents) was reported, with a very different mechanism, single electron transfer living radical polymerization (SET-LRP) postulated by Virgil Percec.<ref name=Percec2006>{{cite journal|last1=Percec|first1=Virgil|last2=Guliashvili|first2=Tamaz|last3=Ladislaw|first3=Janine S.|last4=Wistrand|first4=Anna|last5=Stjerndahl|first5=Anna|last6=Sienkowska|first6=Monika J.|last7=Monteiro|first7=Michael J.|last8=Sahoo|first8=Sangrama|title=Ultrafast Synthesis of Ultrahigh Molar Mass Polymers by Metal-Catalyzed Living Radical Polymerization of Acrylates, Methacrylates, and Vinyl Chloride Mediated by SET at 25 °C|journal=Journal of the American Chemical Society|date=November 2006|volume=128|issue=43|pages=14156–14165|doi=10.1021/ja065484z|pmid=17061900}}</ref> Initiated by this mechanistic difference, many research articles were published during recent years which aimed to shed a light on this specific polymerization reaction, and the discussion of the mechanisms has been a very striking episode in the field of polymer science.<ref name=gao2014>{{cite journal|last1=Gao|first1=Yongsheng|last2=Zhao|first2=Tianyu|last3=Wang|first3=Wenxin|title=Is it ATRP or SET-LRP? part I: Cu &Cu /PMDETA – mediated reversible – deactivation radical polymerization|journal=RSC Adv.|date=11 November 2014|volume=4|issue=106|pages=61687–61690|doi=10.1039/C4RA11477A}}</ref><ref name=Maty2013MM>{{cite journal|last1=Konkolewicz|first1=Dominik|last2=Wang|first2=Yu|last3=Zhong|first3=Mingjiang|last4=Krys|first4=Pawel|last5=Isse|first5=Abdirisak A.|last6=Gennaro|first6=Armando|last7=Matyjaszewski|first7=Krzysztof|title=Reversible-Deactivation Radical Polymerization in the Presence of Metallic Copper. A Critical Assessment of the SARA ATRP and SET-LRP Mechanisms|journal=Macromolecules|date=26 November 2013|volume=46|issue=22|pages=8749–8772|doi=10.1021/ma401243k|bibcode=2013MaMol..46.8749K}}</ref><ref>{{cite journal|last1=Konkolewicz|first1=Dominik|last2=Wang|first2=Yu|last3=Krys|first3=Pawel|last4=Zhong|first4=Mingjiang|last5=Isse|first5=Abdirisak A.|last6=Gennaro|first6=Armando|last7=Matyjaszewski|first7=Krzysztof|title=SARA ATRP or SET-LRP. End of controversy?|journal=Polymer Chemistry|date=2014|volume=5|issue=15|pages=4409|doi=10.1039/C4PY00149D}}</ref><ref>{{cite journal |last1=Anastasaki |first1=Athina |last2=Nikolaou |first2=Vasiliki |last3=Nurumbetov |first3=Gabit |last4=Wilson |first4=Paul |last5=Kempe |first5=Kristian |last6=Quinn |first6=John F. |last7=Davis |first7=Thomas P. |last8=Whittaker |first8=Michael R. |last9=Haddleton |first9=David M. |date=30 July 2015 |title=Cu(0)-Mediated Living Radical Polymerization: A Versatile Tool for Materials Synthesis |journal=Chemical Reviews |volume=116 |issue=3 |pages=835–877 |doi=10.1021/acs.chemrev.5b00191 |pmid=26226544}}</ref>

==Discussion of the mechanism==

===Supplemental activator and reducing agent atom-transfer radical polymerization (SARA ATRP)===
In the case of RDRP reactions in the presence of Cu(0), one of the mechanistic models proposed in the literature is called the supplemental activator and reducing agent atom-transfer radical polymerization (SARA ATRP).<ref name=Maty2013MM/><ref>{{cite journal|last1=Zhang|first1=Yaozhong|last2=Wang|first2=Yu|last3=Peng|first3=Chi-how|last4=Zhong|first4=Mingjiang|last5=Zhu|first5=Weipu|last6=Konkolewicz|first6=Dominik|last7=Matyjaszewski|first7=Krzysztof|title=Copper-Mediated CRP of Methyl Acrylate in the Presence of Metallic Copper: Effect of Ligand Structure on Reaction Kinetics|journal=Macromolecules|date=10 January 2012|volume=45|issue=1|pages=78–86|doi=10.1021/ma201963c|bibcode=2012MaMol..45...78Z}}</ref><ref>{{cite journal|last1=Harrisson|first1=Simon|last2=Couvreur|first2=Patrick|last3=Nicolas|first3=Julien|title=Comproportionation versus Disproportionation in the Initiation Step of Cu(0)-Mediated Living Radical Polymerization|journal=Macromolecules|date=25 September 2012|volume=45|issue=18|pages=7388–7396|doi=10.1021/ma301034t|bibcode=2012MaMol..45.7388H}}</ref> The SARA ATRP is characterized by the traditional ATRP reactions of activation by Cu(I) and deactivation by Cu(II) at the core of the process, with Cu(0) acting primarily as a supplemental activator of alkyl halides and a reducing agent for the Cu(II) through comproportionation. There is minimal kinetic contribution of disproportionation because Cu(I) primarily activates alkyl halides and activation of all alkyl halides occurs by inner sphere electron transfer (ISET).

===Single electron transfer living radical polymerization (SET-LRP)===
Another model is called single-electron transfer living radical polymerization (SET-LRP), where Cu(0) is the exclusive activator of alkyl halides – a process that occurs by outer sphere electron transfer (OSET). The generated Cu(I) disproportionates ‘spontaneously’ into highly reactive ‘nascent’ Cu(0) and Cu(II) species, instead of participating in the activation of alkyl halides, and there is minimal comproportionation.<ref name=Percec2006/><ref name=Percec2009>{{cite journal|last1=Rosen|first1=Brad M.|last2=Percec|first2=Virgil|title=Single-Electron Transfer and Single-Electron Transfer Degenerative Chain Transfer Living Radical Polymerization|journal=Chemical Reviews|date=11 November 2009|volume=109|issue=11|pages=5069–5119|doi=10.1021/cr900024j|pmid=19817375}}</ref>

===Copper(0)-mediated reversible-deactivation radical polymerization (Cu(0)-mediated RDRP)===
One unique experimental phenomenon in the Cu(0)-mediated RDRP systems with Me<sub>6</sub>TREN/DMSO as ligand/solvent is that the existence of an apparent induction period in the early stage and the absence of this induction period was observed by adding extra Cu(II) to the reaction system or employing PMDETA as ligand.<ref name=gao2014/><ref name=gao2015>{{cite journal|last1=Gao|first1=Yongsheng|last2=Zhao|first2=Tianyu|last3=Zhou|first3=Dezhong|last4=Greiser|first4=Udo|last5=Wang|first5=Wenxin|title=Insights into relevant mechanistic aspects about the induction period of Cu /Me TREN-mediated reversible-deactivation radical polymerization|journal=Chem. Commun.|date=2015|volume=51|issue=77|pages=14435–14438|doi=10.1039/C5CC05189D|pmid=26234530}}</ref><ref>{{cite journal|last1=Levere|first1=Martin E.|last2=Willoughby|first2=Ian|last3=O'Donohue|first3=Stephen|last4=de Cuendias|first4=Anne|last5=Grice|first5=Anthony J.|last6=Fidge|first6=Christopher|last7=Becer|first7=C. Remzi|last8=Haddleton|first8=David M.|title=Assessment of SET-LRP in DMSO using online monitoring and Rapid GPC|journal=Polymer Chemistry|date=2010|volume=1|issue=7|pages=1086|doi=10.1039/C0PY00113A}}</ref><ref>{{cite journal|last1=Guliashvili|first1=Tamaz|last2=Mendonça|first2=Patrícia V.|last3=Serra|first3=Arménio C.|last4=Popov|first4=Anatoliy V.|last5=Coelho|first5=Jorge F. J.|title=Copper-Mediated Controlled/"Living" Radical Polymerization in Polar Solvents: Insights into Some Relevant Mechanistic Aspects|journal=Chemistry: A European Journal|date=10 April 2012|volume=18|issue=15|pages=4607–4612|doi=10.1002/chem.201102183|pmid=22378618}}</ref> This intriguing phenomenon cannot be explained either by SARA ATRP or SET-LRP, therefore, another mechanism was proposed by Wenxin Wang: copper(0)-mediated reversible-deactivation radical polymerization (Cu(0)-mediated RDRP).<ref name=gao2015/>

The Cu(0)-mediated RDRP mechanism showed that induction period is originated from the accumulation of soluble copper species during that initial unstable stage. It was demonstrated that Cu(I) act as a powerful activator even under conditions favoring its disproportionation (in Me<sub>6</sub>TREN/DMSO system), whilst  Cu(0) is a supplemental activator and reducing agent and both disproportionation and comproportionation coexist. Cu(II) can be consumed by both the comproportionation and deactivation reaction, the relative extent of which depends on the reactivity of monomers and initiators. 

In Cu(0)-mediated RDRP, two equilibriums coexist under real polymerization conditions – 1) mutual conversion of different copper species which determines the relative concentration of Cu(I) and Cu(II), and 2) polymerization equilibrium which is the combination of activation/deactivation, propagation and termination processes. The synergistic effects of different parameters on both of these equilibria should be considered together, which is crucial to understand the existence of the induction period and the controllability of Cu(0)-mediated RDRP of vinyl monomers with different reactivities.<ref name=Miao2019>{{cite journal|last1=Miao|first1=Yongpeng|last2=lyu|first2=Jing|last3=Yong|first3=Haiyang|last4=Sigen|first4=A|last5=Gao|first5=Yongsheng|last6=Wang|first6=Wenxin|title=Controlled Polymerization of Methyl Methacrylate and Styrene via Cu(0)- Mediated RDRP by Selecting the Optimal Reaction Conditions|journal=Chinese J. Polym. Sci.|date=2019|volume=37|issue=6|pages=591–597|doi=10.1007/s10118-019-2236-x|doi-access=free}}</ref>

Wang et al. has demonstrated that different polymerization parameters including the initiator, solvent, ligand, and the amount of deactivator can affect the controllability of the whole polymerization process by influencing these two equilibriums. Through considering both the mutual conversion among different copper species and the polymerization equilibrium, the optimal reaction conditions were selected for the realization of the well-controlled Cu(0)-mediated RDRPs of methyl methacrylate (MMA) and styrene which are difficult to polymerize based on either the SET-LRP or the SARA ATRP mechanism. The general trends are: for instance, the Cu(0)-mediated RDRP of MMA, either an initiator with relatively low reactivity combined with a higher amount of Cu(II) or a more highly reactive initiator and a lower amount of Cu(II) are needed to achieve the controlled polymerization. The mechanism could be attributed to that the lower k<sub>p</sub> results in a slower establishment of polymerization equilibrium and longer time for copper mutual conversion at the early stage of polymerization. Thus, the small amount of extra Cu(II) added is mostly consumed in the comproportionation process rather than acting as extra deactivator, contributing to the kinetic control.<ref name=Miao2019/>

==See also==
* [[Chemistry:Reversible-deactivation radical polymerization|Reversible-deactivation radical polymerization]]
* Atom-transfer radical-polymerization

==References==
{{reflist|35em}}
<!--- After listing your sources please cite them using inline citations and place them after the information they cite. Please see http://en.wikipedia.org/wiki/Wikipedia:REFB for instructions on how to add citations. --->

<!--- STOP! Be warned that by using this process instead of Articles for Creation, this article is subject to scrutiny. As an article in "mainspace", it will be DELETED if there are problems, not just declined. If you wish to use AfC, please return to the Wizard and continue from there. --->

[[Category:Polymerization reactions]]

{{Sourceattribution|Copper(0)-mediated reversible-deactivation radical polymerization|1}}