8‑Quinolinolato Gallium Complexes: Iso-selective
Initiators for <i>rac</i>-Lactide Polymerization
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Abstract
The
synthesis and characterization of a series of 8-quinolinolato gallium
complexes is presented, and the complexes are analogous to a series
of aluminum complexes previously reported. The complexes have been
shown to be active initiators for the ring-opening polymerization
of <i>rac</i>-lactide. High degrees of polymerization control
are demonstrated, as exemplified by the linear evolution of molecular
weight as the polymerization progresses, narrow polydispersity indices,
and molecular weights corresponding to those predicted on the basis
of initiator concentration. Some of the initiators show iso-selective
polymerization of <i>rac</i>-lactide, with <i>P</i><sub>i</sub> = 0.70. The polymerization rates have been monitored,
and the pseudo first-order rate constants are compared to those of
analogous aluminum compounds. The 8-quinolinolato gallium initiators
show rates approximately 3 times higher than those of the series of
aluminum compounds, while maintaining equivalently high iso-selectivity
(<i>P</i><sub>i</sub> = 0.70) and polymerization control
