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Trinuclear and Tetranuclear Magnesium Alkoxide Clusters as Highly Active Initiators for Ring-Opening Polymerization of l‑Lactide
journal contribution
posted on 2014-01-21, 00:00 authored by Yuan Gao, Zhongran Dai, Jinjin Zhang, Xinxian Ma, Ning Tang, Jincai WuTrinuclear and tetranuclear magnesium
alkoxide clusters supported
by bulky phenolates with triangular or rhombic structures were readily
synthesized in acceptable yields via the reaction of 2-N,N-dimethylaminoethanol/methoxyethanol, different
phenols, and dibutylmagnesium. These complexes have been characterized
using 1H and 13C NMR, elemental analyses, and
X-ray crystallography. The experimental results indicate that these
clusters are efficient and excellent initiators for the ring-opening
polymerizations (ROPs) of l-lactide (LA) and afford polylactides
with desired molecular weights and narrow polydispersity indexes (PDIs).
Complex 2 can even catalyze the ROP of 4000 equiv of l-lactide in 1 min in a controlled model. Kinetic studies indicate
that the polymerization is first-order for both the trinuclear magnesium
complex 3 and LA. However, for the tetranuclear magnesium
complex 5, the polymerization rate is first order for 5 and second order for LA.