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[[File:General scheme ionic prop.png|thumb|600px|General scheme ionic propagation. Propagating center can be radical, cationic or anionic.]]
In [[polymer chemistry]], '''ring-opening polymerization''' ('''ROP''') is a form of [[chain-growth polymerization]] in which the [[End group|terminus]] of a [[polymer]] chain attacks [[cyclic compound|cyclic monomers]] to form a longer polymer (see figure). The reactive center can be [[Radical (chemistry)|radical]], [[anion]]ic or [[cation]]ic
Ring-opening of cyclic monomers is often driven by the relief of [[ring strain|bond-angle strain]]. Thus, as is the case for other types of polymerization, the [[enthalpy]] change in ring-opening is negative.<ref name=Young>{{cite book|last=Young|first=Robert J.|title=Introduction to Polymers|year=2011|publisher=CRC Press|location=Boca Raton|isbn=978-0-8493-3929-5}}</ref> Many rings undergo ROP.<ref>{{cite journal |doi=10.1007/s00726-006-0432-9}}</ref>
==Monomers==
Many [[cyclic compound|
</ref> and [[amino acid N-carboxyanhydride|amino acid ''N''-carboxyanhydride]]s.<ref>{{cite journal|author=Kricheldorf, H. R. |year=2006 |title=Polypeptides and 100 Years of Chemistry of α-Amino Acid ''N''-Carboxyanhydrides|journal=Angewandte Chemie International Edition |volume=45|issue=35|pages=5752–5784|doi= 10.1002/anie.200600693|pmid=16948174 }}</ref><ref>{{cite journal|title=Synthesis of Well-Defined Polypeptide-Based Materials via the Ring-Opening Polymerization of α-Amino Acid N-Carboxyanhydrides|author=Nikos Hadjichristidis |author2=Hermis Iatrou |author3=Marinos Pitsikalis |author4=Georgios Sakellariou |journal=Chemical Reviews|year=2009|volume=109|issue=11|pages= 5528–5578|doi=10.1021/cr900049t|pmid=19691359}}</ref> Many strained [[cycloalkene]]s, e.g [[norbornene]], are suitable monomers via [[ring-opening metathesis polymerization]]. Even highly strained [[cycloalkane]] rings, such as [[cyclopropane]]<ref>{{cite journal |title= The Polymerization of Cyclopropane |first1= R. J. |last1= Scott |first2= H. E. |last2= Gunning |journal= J. Phys. Chem. |year= 1952 |volume= 56 |issue= 1 |pages= 156–160 |doi= 10.1021/j150493a031 }}</ref> and [[cyclobutane]]<ref>{{cite journal |title= Ring-Opening Polymerization of the Cyclobutane Adduct of Methyl Tricyanoethylenecarboxylate and Ethyl Vinyl Ether |first1= Tsutomu |last1= Yokozawa |first2= Ei-ichi |last2= Tsuruta |journal= Macromolecules |year= 1996 |volume= 29 |issue= 25 |pages= 8053–8056 |doi= 10.1021/ma9608535 }}</ref> derivatives, can undergo ROP.
==History==
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===Anionic ring-opening polymerization (AROP)===
{{main article|Anionic polymerization}}
[[File:Wiki566665.tif|thumb|400px|center|The general mechanism for anionic ring-opening polymerization. Polarized functional group is represented by X-Y, where the atom X (usually a carbon atom) becomes electron deficient due to the highly electron-withdrawing nature of Y (usually an oxygen, nitrogen, sulfur, etc.). The nucleophile will attack atom X, thus releasing Y
Anionic ring-opening polymerizations (AROP) involve [[nucleophile|nucleophilic reagents]] as initiators. Monomers with a three-member ring structure - such as [[epoxides]], [[aziridines]], and [[episulfides]] - undergo anionic ROP.<ref name=dubois />
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===Ring-opening metathesis polymerization===
{{main article|Ring-opening metathesis polymerization}}
[[Ring-opening metathesis polymerisation
The mechanism for ROMP follows similar pathways as [[olefin metathesis]]. The initiation process involves the coordination of the cycloalkene monomer to the [[Transition metal carbene complex|metal alkylidene complex]], followed by a [2+2] type [[cycloaddition]] to form the metallacyclobutane intermediate that cycloreverts to form a new alkylidene species.<ref name=sutthasupa>{{cite journal|last=Sutthasupa|first=Sutthira|author2=Shiotsuki, Masashi |author3=Sanda, Fumio |title=Recent advances in ring-opening metathesis polymerization, and application to synthesis of functional materials|journal=Polymer Journal|date=13 October 2010|volume=42|issue=12|pages=905–915|doi=10.1038/pj.2010.94|doi-access=free}}</ref><ref name=hartwig>{{cite book|last=Hartwig|first=John F.| author-link = John F. Hartwig | title=Organotransition metal chemistry: from bonding to catalysis|year=2010|publisher=University Science Books|location=Sausalito, California|isbn=978-1-891389-53-5}}</ref>
[[File:Romp mechanism.png|thumb|center|850px|General scheme of the mechanism for ROMP.]] Commercially relevant [[Saturated and unsaturated compounds|unsaturated]] polymers synthesized by ROMP include
==Thermodynamics==
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For example, [[tetrahydrofuran]] (THF) cannot be polymerized above {{mvar|T<sub>c</sub>}} = 84 °C, nor cyclo-octasulfur (S<sub>8</sub>) below {{mvar|T<sub>f</sub>}} = 159 °C.<ref>{{cite journal|last=Tobolsky|first=A. V.|title=Equilibrium polymerization in the presence of an ionic initiator|journal=Journal of Polymer Science|date=July 1957|volume=25|issue=109|pages=220–221|doi=10.1002/pol.1957.1202510909|bibcode=1957JPoSc..25..220T}}</ref><ref>{{cite journal|last=Tobolsky|first=A. V.|title=Equilibrium polymerization in the presence of an ionic initiator|journal=Journal of Polymer Science|date=August 1958|volume=31|issue=122|page=126|doi=10.1002/pol.1958.1203112214|bibcode=1958JPoSc..31..126T|doi-access=free}}</ref><ref>{{cite journal|last=Tobolsky|first=Arthur V.|author2=Eisenberg, Adi |title=Equilibrium Polymerization of Sulfur|journal=Journal of the American Chemical Society|date=May 1959|volume=81|issue=4|pages=780–782|doi=10.1021/ja01513a004}}</ref><ref>{{cite journal|last=Tobolsky|first=A. V.|author2=Eisenberg, A. |title=A General Treatment of Equilibrium Polymerization|journal=Journal of the American Chemical Society|date=January 1960|volume=82|issue=2|pages=289–293|doi=10.1021/ja01487a009}}</ref> However, for many monomers, {{mvar|T<sub>c</sub>}} and {{mvar|T<sub>f</sub>}}, for polymerization in the bulk, are well above or below the operable polymerization temperatures, respectively.
The polymerization of a majority of monomers is accompanied by an [[entropy]] decrease, due mostly to the loss in the translational degrees of freedom. In this situation, polymerization is thermodynamically allowed only when the enthalpic contribution into {{math|Δ''G<sub>p</sub>''}} prevails (thus, when {{math|Δ''H<sub>p</sub>''° < 0}} and {{math|Δ''S<sub>p</sub>''° < 0}}, the inequality {{math|{{abs|Δ''H<sub>p</sub>''}} > −''T''Δ''S<sub>p</sub>''}} is required). Therefore, the higher the ring strain, the lower the resulting monomer concentration at [[Chemical equilibrium|equilibrium]].
==Additional reading==
*{{Cite book |title=Expanding Monomers: Synthesis, Characterization, and Applications |title-link=Expanding Monomers |publisher=CRC Press |year=1992 |isbn=978-0-8493-5156-3 |editor-last=Luck |editor-first=Russel M. |editor-last2=Sadhir |editor-first2=Rajender K. |location=Boca Raton, Florida}}
*{{cite journal|
*{{cite book |title= Handbook of Ring‐Opening Polymerization |editor1-first= Philippe |editor1-last= Dubois |editor2-first= Olivier |editor2-last= Coulembier |editor3-first= Jean-Marie |editor3-last= Raquez |publisher= Wiley |year= 2009 |isbn= 9783527628407 |doi= 10.1002/9783527628407 }}<!-- see especially chapter 13 "Polymerization of Cycloalkanes" lead-ref for expanding our article -->
== References ==
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