Synthesis of aliphatic polyesters by organometallic catalysis

As biodegradable or biocompatible polymers, aliphatic polyesters find a wide range of practical applications, from packaging to more sophisticated biomedical devices. The synthesis can be achieved via ring-opening polymerization (ROP) of cyclic esters, as L-lactide, D,L-lactide, -caprolactone, glycolide and -butyrolactone, a process initiated by a large variety of species, ranging from metal complexes to nucleophilic organocatalysts, to enzymes.[1] Our current interest has been devoted to the design of well-defined ROP initiators, with the aim to control the molecular weight and the polymer microstructure, enhance the catalytic activity, and limit deleterious transesterification reactions. Examples of novel ROP initiators based on tin, [2-4] aluminum [5] and rare-earth metal complexes [6] bearing bulky aryl groups, bidentate or tetradentate Schiff-base ligands, phenoxy-thioether ligands, or phosphido pincer ligands will be presented. Emphasis will be given to the mechanistic studies, in particular those concerning the achievement of a controlled and living polymerization, the synthesis of block and random copolymers of -caprolactone and lactides, the stereoselective polymerization of rac--butyrolactone to poly(3-hydroxybutyrate) highly enriched in syndiotactic dyads. References [1] Albertsson, A. C.;Varma, I. K. Biomacromol. 2003, 4, 1466–1486. [2] Annunziata, L.; Pappalardo, D.; Tedesco, C.; S. Antinucci, Pellecchia C. J.Organom.Chem., 2006, 691, 8, 1505-1514. [3] Pappalardo, D.; Annunziata, L.; Pellecchia, C.; Bieseman, M.; Willem, R. Macromol. 2007, 40, 1886-1890. [4] Gorrasi, G.; Vertuccio, L.; Annunziata, L.; Pellecchia, C.; Pappalardo, D. Reac. Funct. Pol. 2010, 70, 151-158. [5] Pappalardo, D.; Annunziata, L.; Pellecchia, C. Macromol. 2009, 42, 6056-6062. [6] D’Auria, I.; Mazzeo, M.; Pappalardo, D.; Lamberti, M.; Pellecchia, C. J. Pol. Sci. 2011, 49, 403-413.