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Highly Active Chiral Oxazolinyl Aminophenolate Magnesium Initiators for Isoselective Ring-Opening Polymerization of rac-Lactide: Dinuclearity Induced Enantiomorphic Site Control
journal contribution
posted on 2018-07-11, 18:33 authored by Jianwen Hu, Chao Kan, Haobing Wang, Haiyan MaThe most important challenge in ring-opening
polymerization of rac-lactide today is to obtain
isotactic PLAs with high
molecular weights. The goal of our work is to address this important
challenge by developing novel catalysts that enable precise control
over stereoselectivity and produce high molecular weight PLAs at the
same time. Here we report some rare examples of isoselective magnesium
complexes toward the ROP of rac-LA, which are supported
by chiral oxazolinyl aminophenolate ligands. Preliminary kinetic investigations
confirmed that isotactic PLAs could be achieved via an enantiomorphic
site control mechanism by using these chiral magnesium complexes.
A pair of racemic magnesium initiators proved to integrate hyperactivity
(TOF up to 54 000 h–1 at 25 °C) with
sufficient isoselectivity (Pm = 0.80)
toward the ROP of rac-LA, leading to the formation
of isotactic stereoblock PLA with high molecular weight (Mn = 461 kg mol–1) and a semicrystalline
property (Tm = 164 °C). Detailed
structural investigation on the magnesium lactate model complexes
suggested that the high degree of enantiomorphic site control is derived
from both the ligand chirality and the dinuclear feature of the magnesium
active species.
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chiral magnesium complexesActive Chiral Oxazolinyl Aminophenolate Magnesium Initiatorsenantiomorphic site controlracemic magnesium initiatorsinvestigationROPDinuclearity Induced Enantiomorphic Site Controlenantiomorphic site control mechanismchallengeisoselective magnesium complexesisotactic PLAsisotactic stereoblock PLAIsoselective Ring-Opening Polymerizationchiral oxazolinyl aminophenolate ligandsTOFmagnesium lactate model complexes
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