Theoretical Investigation of Lactide Ring-Opening
Polymerization Induced by a Dinuclear Indium Catalyst
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Abstract
A DFT study of the ring-opening polymerization
of lactide (LA) induced by a dinuclear indium catalyst supported by
a chiral diamino phenoxy ligand, [(NN<sub>H</sub>O)InCl]<sub>2</sub>(μ-Cl)(μ-OEt) (<b>1</b>), is reported. The nature
of the active catalyst, mononuclear vs dinuclear, was investigated
and was shown to be dinuclear because of the high energetic cost of
its dissociation. The selectivity of the system was investigated for
the polymerization of LA with the dinuclear (<i>R,R</i>/<i>R,R</i>)-<b>1</b> catalyst. In complete agreement with
experimental results we observed that (1) selectivity is controlled
by the nucleophilic addition of LA to the alcoholate, resulting in
the chain-end control of polymerization, (2) a slight kinetic preference
for the polymerization of l-LA over d-LA is found
that translates to a <i>k</i><sub>rel</sub> value of ∼14,
which is identical with the experimental value, and (3) when <i>rac</i>-LA is used, no clear preference for d- vs l-LA insertion is found, leading to isotactic PLA