title: Highly Stereocontrolled Ring-Opening Polymerization of Racemic Alkyl β-Malolactonates Mediated by Yttrium [Amino-alkoxy-bis(phenolate)] Complexes.
abstract: Yttrium [amino-alkoxy-bis(phenolate)]amido complexes have been used for the ring-opening polymerization (ROP) of racemic alkyl β-malolactonates (4-alkoxycarbonyl-2-oxetanones, rac-MLA(R) s) bearing an allyl (All), benzyl (Bz) or methyl (Me) lateral ester function. The nature of the ortho-substituent on the phenolate rings in the metal ancillary dictated the stereocontrol of the ROP, and consequently the syndiotactic enrichment of the resulting polyesters. ROP promoted by catalysts with halogen (Cl, Br)-disubstituted ligands allowed the first reported synthesis of highly syndiotactic PMLA(R) s (Pr ≥ 0.95); conversely, catalysts bearing bulky alkyl and aryl ortho-substituted ligands proved largely ineffective. All polymers have been characterized by (1) H and (13) C{(1) H} NMR spectroscopy, MALDI-ToF mass spectrometry and DSC analyses. Statistical and thermal analyses enabled the rationalization of the chain-end control mechanism. Whereas the stereocontrol of the polymerization obeyed a Markov first-order (Mk1) model for the ROP of rac-MLA(Bz) and rac-MLA(All) , the ROP of rac-MLA(Me) led to a chain end-control of Markov second-order type (Mk2). DFT computations suggest that the high stereocontrol ability featured by catalysts bearing Cl- and Br-substituted ligands does not likely originate from halogen bonding between the halogen substituent and the growing polyester chain.
authors.affiliation: Institut des Sciences Chimiques de Rennes, Organometallics: Materials and Catalysis Laboratories, UMR 6226 CNRS-Université de Rennes 1, Campus de Beaulieu, 35042, Rennes Cedex, France.
authors.forename: Cédric G
authors.initials: CG
authors.lastname: Jaffredo
authors.affiliation: Institut des Sciences Chimiques de Rennes, Organometallics: Materials and Catalysis Laboratories, UMR 6226 CNRS-Université de Rennes 1, Campus de Beaulieu, 35042, Rennes Cedex, France.
authors.forename: Yulia
authors.initials: Y
authors.lastname: Chapurina
authors.affiliation: Institut des Sciences Chimiques de Rennes, Organometallics: Materials and Catalysis Laboratories, UMR 6226 CNRS-Université de Rennes 1, Campus de Beaulieu, 35042, Rennes Cedex, France.
authors.forename: Evgueni
authors.initials: E
authors.lastname: Kirillov
authors.affiliation: Institut des Sciences Chimiques de Rennes, Organometallics: Materials and Catalysis Laboratories, UMR 6226 CNRS-Université de Rennes 1, Campus de Beaulieu, 35042, Rennes Cedex, France. jean-francois.carpentier@univ-rennes1.fr.
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Carpentier
authors.affiliation: Institut des Sciences Chimiques de Rennes, Organometallics: Materials and Catalysis Laboratories, UMR 6226 CNRS-Université de Rennes 1, Campus de Beaulieu, 35042, Rennes Cedex, France. sophie.guillaume@univ-rennes1.fr.
authors.forename: Sophie M
authors.identifier: http://orcid.org/0000-0003-2917-8657
authors.initials: SM
authors.lastname: Guillaume
keywords: density functional calculations; lactones; polymers; ring-opening polymerization; yttrium