Chromium(III) Amino-bis(phenolate) Catalysts for the Ring-Opening Copolymerization of Epoxides and Phthalic Anhydride: Effects of Cocatalysts and Cyclohexene Oxide Initiators on Copolymerization Activity

The amino-bis(phenolate) chromium(III) “ate” complex {Na[CrCl 2 L1 ]}, Na[ 1 Cl], where [ L1 ] = 6,6′-((1,4-diazepane-1,4-diyl)bis(methylene))bis(2,4-di- tert -butylphenolato) and the similar amino-bis(phenolate) chromium(III) complex CrCl[ L1 ], 2 where [ L2 ] = 6,6′-((1,4-diazepane-1,4-diyl)bis(methylene))bis(2,4-dimethylphenolato) both show good activity for the ring-opening copolymerization (ROCOP) of epoxides with phthalic anhydride (PA). These complexes react with bis(triphenylphosphine)iminium chloride to form bis(triphenylphosphine)iminium chromium(III) dichloride “ate” complexes, PPN[ 1 Cl] and PPN[ 2 Cl], that show further control and selectivity for the ROCOP reactions. The influence of cocatalyst, solvent, catalyst loading, and presence of a second epoxide for initiation of the ROCOP reaction were studied. The ate-complex PPN[ 1 Cl] catalyzes a faster polyester formation using propylene oxide and PA by using the more reactive cyclohexene oxide as an initiator. These polyesters have moderate molar masses, high conversions of PA to polyester, excellent selectivity, and narrow dispersity values (e.g., M n = 6.8 kg mol –1 and Đ = M w / M n = 1.13).