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dc.contributor.authorZhang, Yuetao
dc.contributor.authorSchmitt, Meghan L.
dc.contributor.authorFalivene, Laura
dc.contributor.authorCaporaso, Lucia
dc.contributor.authorCavallo, Luigi
dc.contributor.authorChen, Eugene You Xian
dc.date.accessioned2015-08-03T11:35:56Z
dc.date.available2015-08-03T11:35:56Z
dc.date.issued2013-11-18
dc.identifier.issn00027863
dc.identifier.doi10.1021/ja4088677
dc.identifier.urihttp://hdl.handle.net/10754/563107
dc.description.abstractThis contribution presents a full account of experimental and theoretical/computational investigations into the mechanisms of chain initiation, propagation, and termination of the recently discovered N-heterocyclic carbene (NHC)-mediated organocatalytic conjugate-addition polymerization of acrylic monomers. The current study specifically focuses on three commonly used NHCs of vastly different nucleophilicity, 1,3-di-tert-butylimidazolin-2-ylidene (ItBu), 1,3- dimesitylimidazolin-2-ylidene (IMes), and 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4- triazol-5-ylidene (TPT), and two representative acrylic monomers, the linear methyl methacrylate (MMA) and its cyclic analog, biomass-derived renewable γ-methyl-α-methylene-γ-butyrolactone (MMBL). For MMA, there exhibits an exquisite selectivity of the NHC structure for the three types of reactions it promotes: enamine formation (single-monomer addition) by IMes, dimerization (tail-to-tail) by TPT, and polymerization by ItBu. For MMBL, all three NHCs promote no dimerization but polymerization, with the polymerization activity being highly sensitive to the NHC structure and the solvent polarity. Thus, ItBu is the most active catalyst of the series and converts quantitatively 1000-3000 equiv of MMBL in 1 min or 10 000 equiv in 5 min at room temperature to MMBL-based bioplastics with a narrow range of molecular weights of Mn = 70-85 kg/mol, regardless of the [MMBL]/[ItBu] ratio employed. The ItBu-catalyzed MMBL polymerization reaches an exceptionally high turnover frequency up to 122 s -1 and a high initiator efficiency value up to 1600%. Unique chain-termination mechanisms have been revealed, accounting for the production of relative high-molecular-weight linear polymers and the catalytic nature of this NHC-mediated conjugate-addition polymerization. Computational studies have provided mechanistic insights into reactivity and selectivity between two competing pathways for each NHC-monomer zwitterionic adduct, namely enamine formation/dimerization through proton transfer vs polymerization through conjugate addition, and mapped out extensive energy profiles for chain initiation, propagation, and termination steps, thereby satisfactorily explaining the experimental observations. © 2013 American Chemical Society.
dc.description.sponsorshipThis work was supported by the National Science Foundation (NSF-1012326 and NSF-1300267) for the study carried out at Colorado State University. L.C. thanks the HPC team of Enea (www.enea.it) for using the ENEA-GRID and the HPC facilities CRESCO (www.cresco.enea.it) in Portici, Italy.
dc.publisherAmerican Chemical Society (ACS)
dc.titleOrganocatalytic conjugate-addition polymerization of linear and cyclic acrylic monomers by N-heterocyclic carbenes: Mechanisms of chain initiation, propagation, and termination
dc.typeArticle
dc.contributor.departmentChemical Science Program
dc.contributor.departmentKAUST Catalysis Center (KCC)
dc.contributor.departmentPhysical Science and Engineering (PSE) Division
dc.identifier.journalJournal of the American Chemical Society
dc.contributor.institutionDepartment of Chemistry, Colorado State University, Fort Collins, CO 80523-1872, United States
dc.contributor.institutionDipartimento di Chimica e Biologia, Università di Salerno, I-84084, Fisciano, Italy
kaust.personCavallo, Luigi
dc.relation.issupplementedbyDOI:10.5517/cc11431b
display.relations<b> Is Supplemented By:</b> <br/> <ul><li><i>[Dataset]</i> <br/> Zhang, Y., Schmitt, M., Falivene, L., Caporaso, L., Cavallo, L., & Chen, E. Y.-X. (2014). CCDC 957250: Experimental Crystal Structure Determination [Data set]. Cambridge Crystallographic Data Centre. https://doi.org/10.5517/cc11431b. DOI: <a href="https://doi.org/10.5517/cc11431b">10.5517/cc11431b</a> HANDLE: <a href="http://hdl.handle.net/10754/624258">10754/624258</a></li></ul>
dc.date.published-online2013-11-18
dc.date.published-print2013-11-27


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