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==History==
'''Ring-opening polymerization''' ('''ROP''') has been used since the beginning of the 1900s in order to synthesize [[polymer]]s. Synthesis of [[polypeptides]] which has the oldest history of ROP, dates back to the work in 1906 by Leuchs.<ref>{{cite journal|title=Glycine-carbonic acid|last=Leuchs|first=H.|journal=Ber. Dtsch. Chem.|year=1906|volume=39|page=857}}</ref> Many years later came the method of the ROP of anhydro [[sugars]], providing [[polysaccharides]], including synthetic [[dextran]], [[xanthan gum]], [[welan gum]], [[gellan gum]], diutan gum, and [[pullulan]]. Mechanisms and thermodynamics of ring-opening polymerization was further established in the 1950s.<ref>{{cite journal|last=Dainton|first=F. S.|author2=Devlin, T. R. E. |author3=Small, P. A. |title=The thermodynamics of polymerization of cyclic compounds by ring opening|journal=Transactions of the Faraday Society|year=1955|volume=51|pages=1710|doi=10.1039/TF9555101710}}</ref><ref>{{cite journal|last=Conix|first=André|author2=Smets, G. |title=Ring opening in lactam polymers|journal=Journal of Polymer Science|date=January 1955|volume=15|issue=79|pages=221–229|doi=10.1002/pol.1955.120157918|bibcode=1955JPoSc..15..221C}}</ref> The first high-molecular weight polymers (M<sub>n</sub> up to 10<sup>5</sup>) with a [[repeat unit|repeating unit]] were prepared by ROP as early as in 1976.<ref>{{cite journal|last1= Kałuz̀ynski|first1=Krzysztof|last2=Libiszowski|first2=Jan|last3=Penczek|first3=Stanisław|title=Poly(2-hydro-2-oxo-1,3,2-dioxaphosphorinane). Preparation and NMR spectra|journal=Die Makromolekulare Chemie|volume=178|issue=10|year=1977|pages=2943–2947|issn=0025-116X|doi=10.1002/macp.1977.021781017}}</ref>
<ref>{{cite journal|last=Libiszowski|first=Jan|author2=Kałużynski, Krzysztof |author3=Penczek, Stanisław |title=Polymerization of cyclic esters of phosphoric acid. VI. Poly(alkyl ethylene phosphates). Polymerization of 2-alkoxy-2-oxo-1,3,2-dioxaphospholans and structure of polymers|journal=Journal of Polymer Science: Polymer Chemistry Edition|date=June 1978|volume=16|issue=6|pages=1275–1283|doi=10.1002/pol.1978.170160610|bibcode=1978JPoSA..16.1275L}}</ref>
Nowadays, ROP plays an important role in industry such as production of [[nylon-6]]. ROP can introduce [[functional group]]s such as [[ether]], [[ester]], [[amide]], and [[carbonate]] into the polymer main chain, which cannot be achieved by [[vinyl polymer]]ization affording polymers only with C-C main chain. Polymers obtained by ROP can be also prepared by [[polycondensation]] in most cases, but following [[controlled radical polymerization]] is possible in ROP, which is difficult in polycondensation.
Recently, development of novel [[monomer]]s and [[Catalysis|catalysts]] has enabled polymer chemists to control [[molecular mass|molecular weights]], structure, and configuration of the polymers precisely.<ref>{{cite book|last=Luck|first=edited by Rajender K. Sadhir, Russell M.|title=[[Expanding Monomers]]: Synthesis, Characterization, and Applications|year=1992|publisher=CRC Press|location=Boca Raton, Florida|isbn=9780849351563}}</ref> Cyclic carbonates undergo both [[cationic polymerization]] and [[anionic polymerization]] to afford the corresponding [[polycarbonates]], which are expected as biocompatible and biodegradable polymers.<ref>{{cite journal|last=Matsumura|first=Shuichi|author2=Tsukada, Keisuke |author3=Toshima, Kazunobu |title=Enzyme-Catalyzed Ring-Opening Polymerization of 1,3-Dioxan-2-one to Poly(trimethylene carbonate)|journal=Macromolecules|date=May 1997|volume=30|issue=10|pages=3122–3124|doi=10.1021/ma961862g|bibcode=1997MaMol..30.3122M}}</ref>
Recently, ultra high molecular weight bisphenol A polycarbonate (> 2,000 kDa) has been synthesized by ROP of a large-membered bisphenol A-based [[cyclic carbonate]].<ref>{{cite journal|last=Sugiyama|first=J|author2=R. Nagahata |author3=M. Goyal |author4=M. Asai |author5=M. Ueda |author6=K. Takeuchi |journal=ACS Polymer Preprints|year=1998|volume=40|series=1|page=90}}</ref> The resulted polymer can be used as engineering plastics due to its thermal stability and high impact resistance.
When the reactive center of the propagating chain is a [[carbocation]], the polymerization is called '''cationic ring-opening polymerization'''.
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{{main article|Radical polymerization}}
With radical ring-opening polymerization, it is possible to produce polymers of the same or lower density than the monomers. This is important for applications that require constant volume after polymerization, such as [[Dental restoration|tooth fillings]], coatings, and the molding of electrical and electronic components.<ref name=nuyken>{{cite journal|last=Nuyken|first=Oskar|author2=Stephen D. Pask |title=Ring-Opening Polymerization—An Introductory Review|journal=Polymers|date=25 April 2013|volume=5|pages=361–403|doi=10.3390/polym5020361}}</ref> Additionally, radical ROP is useful in producing polymers with [[functional group]]s incorporated in the backbone chain that cannot otherwise be synthesized via conventional [[chain-growth polymerization]] of [[Vinyl group|vinyl]] monomers. For instance, radical ROP can produce polymers with [[ethers]], [[esters]], [[amide]]s, and [[carbonates]] as functional groups along the main chain.<ref name=nuyken /><ref name=dubois>{{cite book|last=Dubois|first=Philippe|title=Handbook of ring-opening polymerization|year=2008|publisher=Wiley-VCH|location=Weinheim|isbn=978-3-527-31953-4|edition=1. Aufl.}}</ref><ref name=mori>{{cite journal|last=Mori|first=Hideharu|author2=Shigeki Masuda |author3=Takeshi Endo |title=Ring-Opening RAFT Polymerization Based on Aromatization as Driving Force: Synthesis of Well-Defined Polymers Containing Anthracene Units in the Main Chain|journal=Macromolecules|date=July 20, 2006|volume=39|pages=5976–5978|doi=10.1021/ma0612879|bibcode=2006MaMol..39.5976M}}</ref>
[[Radical polymerization|Free radical polymerization]] techniques have been recently developed to control radical ROPs, thereby controlling the [[Molecular mass|molecular weight]] of the synthesized polymer chains. [[Reversible addition−fragmentation chain-transfer polymerization|Reversible Addition Fragmentation Transfer (RAFT)]] has been applied to radical ROP of a cyclopropane monomer.<ref name=dubois /> For instance, the RAFT polymerization of the [[cyclic compound|cyclic monomer]] to synthesize polymers with [[anthracene]] along the backbone chain has been demonstrated.<ref name=mori />
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{{double image|center|Chakyoun_wikiproject_image1.png|350|Chakyoun_wikiproject_image2.png|400|Copolymerization of nonhomopolymerizable monomers, γ-butyrolactone (BL) and ε-caprolactone (CL).|Radical ring-opening copolymerization of a ketene acetal.}}
As an example of copolymerization of non-homopolymerizable monomers, [[γ-butyrolactone]] (BL) and [[ε-caprolactone]] (CL) show that the copolymerization provides high molar mass polymers: The BL/CL copolymer synthesis is viable despite the fact that BL monomer addition to its own –bl* active chain ends was highly reversible, as the –bl* unit could be blocked via a practically irreversible CL addition.<ref>{{cite journal|last=Duda|first=Andrzej|author2=Penczek, Stanislaw |author3=Dubois, Philippe |author4=Mecerreyes, David |author5= Jérôme, Robert |title=Oligomerization and copolymerization of γ-butyrolactone — a monomer known as unable to homopolymerize, 1. Copolymerization with ɛ-caprolactone|journal=Macromolecular Chemistry and Physics|date=April 1996|volume=197|issue=4|pages=1273–1283|doi=10.1002/macp.1996.021970408}}</ref><ref>{{cite journal|last=Ubaghs|first=Luc|author2=Waringo, Michel |author3=Keul, Helmut |author4= Höcker, Hartwig |title=Copolymers and Terpolymers of Tetramethylene Urea, γ-Butyrolactone, and Ethylene Carbonate or 1,2-Propylene Carbonate|journal=Macromolecules|date=September 2004|volume=37|issue=18|pages=6755–6762|doi=10.1021/ma049668e|bibcode=2004MaMol..37.6755U}}</ref><ref>{{cite journal|last=Agarwal|first=Seema|author2=Xie, Xiulan |title=SmI/Sm-Based γ-Buyrolactone−ε-Caprolactone Copolymers: Microstructural Characterization Using One- and Two-Dimensional NMR Spectroscopy|journal=Macromolecules|date=May 2003|volume=36|issue=10|pages=3545–3549|doi=10.1021/ma0258713|bibcode=2003MaMol..36.3545A}}</ref>
Similarly, the earlier studies of S<sub>8</sub> copolymerization with [[thiiranes]] (propylene sulfide; PS), at temperatures below T<sub>f</sub> for S<sub>8</sub> homopolymerization, revealed that the average [[sulfur]] rank in the copolymer was increased from 1 to 7 when 8[S<sub>8</sub>]<sub>0</sub>/[PS]<sub>0</sub> ratio was increasing from 0 to 10.<ref>{{cite journal|last=PENCZEK|first=STANISŁAW|author2=ŚLAZAK, ROMUALD |author3=DUDA, ANDRZEJ |title=Anionic copolymerisation of elemental sulphur|journal=Nature|date=29 June 1978|volume=273|issue=5665|pages=738–739|doi=10.1038/273738a0|bibcode=1978Natur.273..738P}}</ref><ref>{{cite journal|last=Duda|first=Andrzej|author2=Penczek, Stanislaw |title=Anionic copolymerization of elemental sulfur with propylene sulfide|journal=Macromolecules|date=January 1982|volume=15|issue=1|pages=36–40|doi=10.1021/ma00229a007|bibcode=1982MaMol..15...36D}}</ref>
==Thermodynamics==
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:<math>T_c = \frac{\Delta H^\circ_p}{\Delta S^\circ_p + R\ln[M]_0} ; (\Delta H^\circ_p<0, \Delta S^\circ_p<0)</math>
:<math>T_f = \frac{\Delta H^\circ_p}{\Delta S^\circ_p + R\ln[M]_0} ; (\Delta H^\circ_p>0, \Delta S^\circ_p>0)</math>
For example, [[tetrahydrofuran]] (THF) cannot be polymerized above T<sub>c</sub> = 84 °C, nor cyclo-octasulfur (S<sub>8</sub>) below 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|pages=126–126|doi=10.1002/pol.1958.1203112214|bibcode=1958JPoSc..31..126T}}</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, T<sub>c</sub> and 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 ΔG<sub>p</sub> prevails (thus, when ΔH<sub>p</sub>° < 0 and ΔS<sub>p</sub>° < 0, the inequality |ΔH<sub>p</sub>| > -TΔS<sub>p</sub> is required). Therefore, the higher the ring strain, the lower the resulting monomer concentration at [[Chemical equilibrium|equilibrium]].
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