A New Role for CO2: Controlling Agent of the Anionic Ring-Opening Polymerization of Cyclic Esters

Handle URI:
http://hdl.handle.net/10754/625737
Title:
A New Role for CO2: Controlling Agent of the Anionic Ring-Opening Polymerization of Cyclic Esters
Authors:
Varghese, Jobi K.; Goncalves, Theo; Huang, Kuo-Wei ( 0000-0003-1900-2658 ) ; Hadjichristidis, Nikolaos ( 0000-0003-1442-1714 ) ; Gnanou, Yves ( 0000-0001-6253-7856 ) ; Feng, Xiaoshuang
Abstract:
Conventional anionic ring-opening of polymerization (AROP) of cyclic esters suffers from the nonselective and concomitant attack of the monomer and of the polymer chains by the growing active species, which results in polyester samples with uncontrolled molar masses and broad polydispersity due to the competition between propagation and transesterification reactions. In this report, we describe a new AROP system mediated by a controlled amount of CO2 which prevents transesterification reactions from occurring. Using lithium monomethyl diethylene glycoxide (MEEOLi) as initiator and 1.5 equiv of CO2, ε-caprolactone could be polymerized under truly “living” conditions in dichloromethane (DCM) at 70 °C, as evidenced by the control of molar masses, the narrow polydispersity indexes (Mn up to ∼40 kg/mol, Đ < 1.16), and also successful chain extension experiments. Lithium carbonate used as initiator in the presence of 0.5 equiv of CO2 afforded similar polymerization results. Experiments carried out with other alkoxide salts and solvents demonstrate that CO2 is indispensable as well as lithium and noncoordinating solvents for the suppression of transesterifications. A similar strategy was applied for the AROP of l-lactide (LLA). At −20 °C, LLA could be polymerized under living conditions with undetectable level of transesterification as demonstrated by MALDI-ToF analysis. To account for the polymerization mechanism occurring in the presence of a slight excess of CO2, we resorted to computational studies. It appears that a fast equilibrium takes place between two tetrameric aggregates, one dormant comprising four carbonates (RCO3Li)4, and an active one involving three carbonates and one alkoxide (RCO3Li)3(ROLi). The latter is shown to selectively ring-open cyclic ester without indulging in transesterifications like (ROLi)4 precursors.
KAUST Department:
KAUST Catalysis Center (KCC); Physical Sciences and Engineering (PSE) Division
Citation:
Varghese JK, Gonçalves TP, Huang K-W, Hadjichristidis N, Gnanou Y, et al. (2017) A New Role for CO2: Controlling Agent of the Anionic Ring-Opening Polymerization of Cyclic Esters. Macromolecules 50: 6752–6761. Available: http://dx.doi.org/10.1021/acs.macromol.7b01425.
Publisher:
American Chemical Society (ACS)
Journal:
Macromolecules
Issue Date:
15-Aug-2017
DOI:
10.1021/acs.macromol.7b01425
Type:
Article
ISSN:
0024-9297; 1520-5835
Sponsors:
This research work is supported by KAUST under baseline funding (BAS/1/1374-01-01). We are very grateful to Dr. Xianrong Guo (core lab, KAUST) for the help of PFG NMR analysis.
Additional Links:
http://pubs.acs.org/doi/abs/10.1021/acs.macromol.7b01425
Appears in Collections:
Articles; Physical Sciences and Engineering (PSE) Division; KAUST Catalysis Center (KCC)

Full metadata record

DC FieldValue Language
dc.contributor.authorVarghese, Jobi K.en
dc.contributor.authorGoncalves, Theoen
dc.contributor.authorHuang, Kuo-Weien
dc.contributor.authorHadjichristidis, Nikolaosen
dc.contributor.authorGnanou, Yvesen
dc.contributor.authorFeng, Xiaoshuangen
dc.date.accessioned2017-10-03T12:49:36Z-
dc.date.available2017-10-03T12:49:36Z-
dc.date.issued2017-08-15en
dc.identifier.citationVarghese JK, Gonçalves TP, Huang K-W, Hadjichristidis N, Gnanou Y, et al. (2017) A New Role for CO2: Controlling Agent of the Anionic Ring-Opening Polymerization of Cyclic Esters. Macromolecules 50: 6752–6761. Available: http://dx.doi.org/10.1021/acs.macromol.7b01425.en
dc.identifier.issn0024-9297en
dc.identifier.issn1520-5835en
dc.identifier.doi10.1021/acs.macromol.7b01425en
dc.identifier.urihttp://hdl.handle.net/10754/625737-
dc.description.abstractConventional anionic ring-opening of polymerization (AROP) of cyclic esters suffers from the nonselective and concomitant attack of the monomer and of the polymer chains by the growing active species, which results in polyester samples with uncontrolled molar masses and broad polydispersity due to the competition between propagation and transesterification reactions. In this report, we describe a new AROP system mediated by a controlled amount of CO2 which prevents transesterification reactions from occurring. Using lithium monomethyl diethylene glycoxide (MEEOLi) as initiator and 1.5 equiv of CO2, ε-caprolactone could be polymerized under truly “living” conditions in dichloromethane (DCM) at 70 °C, as evidenced by the control of molar masses, the narrow polydispersity indexes (Mn up to ∼40 kg/mol, Đ < 1.16), and also successful chain extension experiments. Lithium carbonate used as initiator in the presence of 0.5 equiv of CO2 afforded similar polymerization results. Experiments carried out with other alkoxide salts and solvents demonstrate that CO2 is indispensable as well as lithium and noncoordinating solvents for the suppression of transesterifications. A similar strategy was applied for the AROP of l-lactide (LLA). At −20 °C, LLA could be polymerized under living conditions with undetectable level of transesterification as demonstrated by MALDI-ToF analysis. To account for the polymerization mechanism occurring in the presence of a slight excess of CO2, we resorted to computational studies. It appears that a fast equilibrium takes place between two tetrameric aggregates, one dormant comprising four carbonates (RCO3Li)4, and an active one involving three carbonates and one alkoxide (RCO3Li)3(ROLi). The latter is shown to selectively ring-open cyclic ester without indulging in transesterifications like (ROLi)4 precursors.en
dc.description.sponsorshipThis research work is supported by KAUST under baseline funding (BAS/1/1374-01-01). We are very grateful to Dr. Xianrong Guo (core lab, KAUST) for the help of PFG NMR analysis.en
dc.publisherAmerican Chemical Society (ACS)en
dc.relation.urlhttp://pubs.acs.org/doi/abs/10.1021/acs.macromol.7b01425en
dc.titleA New Role for CO2: Controlling Agent of the Anionic Ring-Opening Polymerization of Cyclic Estersen
dc.typeArticleen
dc.contributor.departmentKAUST Catalysis Center (KCC)en
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
dc.identifier.journalMacromoleculesen
dc.contributor.institutionPhysical Sciences and Engineering Divisionen
kaust.authorGoncalves, Theoen
kaust.authorHuang, Kuo-Weien
kaust.authorHadjichristidis, Nikolaosen
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