Cyclic Polyesters Formation Using an [OSSO]-Type FeIII catalyst.

The efficient formation of cyclic polyesters from the ring-opening polymerization of lactide, epsilon-caprolactone, and beta-butyrolactone catalyzed by a 1,4-dithiabutanedyl-2,2 '-bis(4,6-dicumylphenol) [OSSO]-FeCl complex activated with cyclohexene oxide was achieved. The catalyst was very active (initial turnover frequency up to 2718 h(-1)), robust, and worked with a monomer/Fe ratio up to 10 000. The formation of cyclic polymers was supported by using high-resolution matrix-assisted laser desorption ionization (MALDI) MS, and the average ring size (approximate to 5 kDa for cyclic polylactide) independent of the reaction conditions. A monometallic ring-opening polymerization/cyclization mechanism was proposed from the results of a kinetic investigation.