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Yttrium Phosphasalen Initiators for rac-Lactide Polymerization
journal contribution
posted on 2013-03-11, 00:00 authored by Clare Bakewell, Thi-Phuong-Anh Cao, Xavier
F. Le Goff, Nicholas J. Long, Audrey Auffrant, Charlotte K. WilliamsA series of highly active yttrium phosphasalen initiators
for the
heteroselective ring-opening polymerization of rac-lactide are reported. The initiators are yttrium alkoxide complexes
ligated by iminophosphorane analogues of the popular “salen”
ligand, termed “phosphasalens”. A series of novel phosphasalens
have been synthesized, with varying substituents on the phenoxide
rings and ethylene, propylene, rac-cyclohexylene, R,R-cyclohexylene, phenylene, and 2,2-dimethylpropylene
groups linking the iminophosphorane moieties. Changing the substituents
on the phosphasalen ligands results in changes to the rates of polymerization
(kobs) and to the PLA heterotacticity
(Ps = 0.87). Generally, the initiators
have high rates, excellent polymerization control, and a tolerance
to low loadings.