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Yttrium Phosphasalen Initiators for rac-Lactide Polymerization: Excellent Rates and High Iso-Selectivities

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journal contribution
posted on 20.02.2016, 03:05 by Clare Bakewell, Thi-Phuong-Anh Cao, Nicholas Long, Xavier F. Le Goff, Audrey Auffrant, Charlotte K. Williams
Highly active yttrium phosphasalen initiators for the stereocontrolled ring-opening polymerization of rac-lactide are reported. The initiators are coordinated by a new class of ancillary ligand: an iminophosphorane derivative of the popular “salen” ligand, termed “phosphasalen”. Changing the phosphasalen structure enables access to high iso-selectivities (Pi = 0.84) or hetero-selectivities (Ps = 0.87). The initiators also show very high rates, excellent polymerization control, and tolerance to low loadings; furthermore, no chiral auxiliaries/ligands are needed for the stereocontrol. The combination of such high rates with high iso-selectivities is very unusual.