Bimetallic Aluminum Complexes Bearing Binaphthyl-Based Iminophenolate Ligands as Catalysts for the Synthesis of Polyesters

Two dinuclear aluminum complexes
bearing dinaphthalene bridging
Schiff bases have been synthesized and investigated as catalysts in
ring-opening polymerization (ROP) of cyclic esters such as rac-lactide (rac-LA) and ε-caprolactone
(ε-CL) and in the copolymerization (ROCOP) of phthalic anhydride
(PA) with cyclohexene oxide (CHO) and limonene oxide (LO). The polymerizations
of cyclic esters were living, producing polymers with narrow molar
mass distributions. Kinetic studies showed that the polymerizations
were first order with respect to the monomers. Cooperative effects
between two metal centers, located in proximal positions, are invoked
to rationalize the high activities toward both monomers, although
the rigid backbone of the complexes enhances the reactivity of less
encumbered caprolactone in comparison to lactide. Good activities
were achieved also in the copolymerization of phthalic anhydride with
cyclohexene epoxide and with the bioderived limonene oxide.