New generation of magnesium complexes for block-stereoblock co-polymers of poly (lactic acid) poly(Ɛ-caprolactone) and poly (ethylene glycol)

Abstract: The bio-degradable nature of the poly (lactic acid) and poly(Ɛ-caprolactone) based polymers calls for their application in various fields. These polymers are typically synthesized via ring opening reaction of the corresponding lactones. An ideal catalyst should combine high activity and living character that would enable the synthesis of block-copolymers by sequential monomer addition. Towards this end, tetradentate monoanionic ligands of the {ONNN}-type with various backbones were synthesized and their reaction with Mg(HMDS)₂ afforded the respective magnesium complexes of the [{ONNN}-Mg(HMDS)] type. In the presence of various alcohol initiators, the magnesium complexes were found to be excellent catalysts for the homo-polymerization of the enantiomers of lactides and Ɛ-caprolactone in a living and immortal fashion. Further, these catalysts were used to prepare various block copolymers of lactide and Ɛ-caprolactone or poly (ethylene glycol) of precise block length and molecular weight.