Highly heteroselective ring-opening polymerization of rac -lactide initiated by rare-earth alkoxides bearing chiral [NNOO]-type amine-bis(phenolate) ligands

A series of new monomeric rare-earth alkoxides (1–6) was successfully synthesized by a one-pot reaction of chiral [NNOO]-type amine-bridged bis(phenolate) ligands (( S )-L 1–4 -H 2 ), Ln[N(SiMe 3 ) 2 ] 3 (Ln = Y, Sm, Nd) and 2-propanol in a 1 : 1 : 1 molar ratio in THF at room temperature. These com...

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Published in:Polymer chemistry 2022-07, Vol.13 (29), p.4249-4259
Main Authors: Duan, Yu-Lai, Guo, Qian, Liu, Gui-Yang, Yi, Zhong-Zhou, Feng, Shao-Ping, Huang, Yong
Format: Article
Language:English
Subjects:
Alkoxides
Crystallography
Infrared spectroscopy
Ligands
Molecular weight distribution
NMR
Nuclear magnetic resonance
Polymer chemistry
Polymerization
Polymers
Rare earth elements
Ring opening polymerization
Room temperature
Spectra
Stereoselectivity
Yttrium
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Summary:A series of new monomeric rare-earth alkoxides (1–6) was successfully synthesized by a one-pot reaction of chiral [NNOO]-type amine-bridged bis(phenolate) ligands (( S )-L 1–4 -H 2 ), Ln[N(SiMe 3 ) 2 ] 3 (Ln = Y, Sm, Nd) and 2-propanol in a 1 : 1 : 1 molar ratio in THF at room temperature. These complexes were well characterized with X-ray crystallography, elemental analyses, IR spectra and NMR spectra in the case of yttrium complexes. Furthermore, complexes 1–6 were employed as efficient initiators for the stereoselective ring-opening polymerization of rac -LA in THF at 20 °C to provide heterotactically enriched polymers ( P r = 0.80–0.95). All of these polymerizations proceeded in a controlled manner, giving polymers with good controlled molecular weights and narrow molecular weight distributions (PDI = 1.03–1.12). The nature of the substituents of the ligands had a profound impact on the reactivity of rare-earth alkoxides but a slight impact on the stereoselectivity. Also, the reactivity and heterotacticity were strongly dependent on the ionic radii of rare-earth metals and polymerization media. The heterotactic and atactic polymers were obtained, respectively, by changing the reaction solvent.
ISSN:1759-9954
1759-9962
DOI:10.1039/D2PY00455K