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 NaCrCl2L1, Na1Cl, 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 CrClL1, 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, PPN1Cl and PPN2Cl, 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 PPN1Cl 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. , Mn = 6. 8 kg mol–1 and Đ = Mw/Mn = 1. 13).