Polymerization of Lactide with Zinc and Magnesium β-Diiminate Complexes: Stereocontrol and Mechanism
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- 16 March 2001
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 123 (14) , 3229-3238
- https://doi.org/10.1021/ja003851f
Abstract
A series of zinc(II) and magnesium(II) alkoxides based upon a β-diiminate ligand framework has been prepared. [(BDI-1)ZnOiPr]2 [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene] exhibited the highest activity and stereoselectivity of the zinc complexes studied for the polymerization of rac- and meso-lactide to poly(lactic acid) (PLA). [(BDI-1)ZnOiPr]2 polymerized (S,S)-lactide to isotactic PLA without epimerization of the monomer, rac-lactide to heterotactic PLA (Pr = 0.94 at 0 °C), and meso-lactide to syndiotactic PLA (Pr = 0.76 at 0 °C). The polymerizations are living, as evidenced by the narrow polydispersities of the isolated polymers in addition to the linear nature of number average molecular weight versus conversion plots and monomer-to-catalyst ratios. The substituents on the β-diiminate ligand exert a significant influence upon the course of the polymerizations, affecting both the degree of stereoselectivity and the rate of polymerization. Kinetic studies with [(BDI-1)ZnOiPr]2 indicate that the polymerizations are first order with respect to monomer (rac-lactide) and 1.56 order in catalyst. Polymerization experiments with [(BDI-1)MgOiPr]2 revealed that this complex is extremely fast for the polymerization of rac-lactide, polymerizing 500 equiv in 96% yield in less than 5 min at 20 °C.Keywords
This publication has 20 references indexed in Scilit:
- Molecular Design of Single-Site Metal Alkoxide Catalyst Precursors for Ring-Opening Polymerization Reactions Leading to Polyoxygenates. 1. Polylactide Formation by Achiral and Chiral Magnesium and Zinc Alkoxides, (η3-L)MOR, Where L = Trispyrazolyl- and Trisindazolylborate LigandsJournal of the American Chemical Society, 2000
- Stereoselective Polymerization of a Racemic Monomer with a Racemic Catalyst: Direct Preparation of the Polylactic Acid Stereocomplex from Racemic LactideJournal of the American Chemical Society, 2000
- Synthesis of disyndiotactic polylactideJournal of Polymer Science Part A: Polymer Chemistry, 1999
- Discrete Yttrium(III) Complexes as Lactide Polymerization CatalystsMacromolecules, 1999
- Synthesis and properties of (D)‐ and (L)‐lactide stereocopolymers using the system achiral Schiff's base/aluminium methoxide as initiatorMacromolecular Chemistry and Physics, 1997
- Highly stereoelective polymerization of rac‐(D,L)‐lactide with a chiral schiff's base/aluminium alkoxide initiatorMacromolecular Chemistry and Physics, 1996
- Microstructure Analysis of Poly(lactic acid) Obtained by Lithium tert-Butoxide as InitiatorMacromolecules, 1995
- Kinetics of polymerization involving reversible deactivation due to aggregation of active centers. Analytical vs. numerical solution for the ε‐caprolactone/dialkylaluminium alkoxide systemMacromolecular Rapid Communications, 1994
- Lithium-6 and nitrogen-15 nuclear magnetic resonance spectroscopic studies of lithiated cyclohexanone phenylimine revisited. Aggregation-state determination by single-frequency nitrogen-15 decouplingJournal of the American Chemical Society, 1990
- Soluble Bimetallic μ-Oxo-alkoxides. 8. Structure and Kinetic Behavior of the Catalytic Species in Unsubstituted Lactone Ring-Opening PolymerizationMacromolecules, 1976