Organocatalytic Stereoselective Ring-Opening Polymerization of Lactide with Dimeric Phosphazene Bases

Highly isotactic polylactide with a high melting temperature was synthesized from rac-lactide through an organocatalytic route using dimeric phosphazene base 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino)-2Λ5,4Λ5-catenadi(phosphazene) (P2-t-Bu) catalyst at low temperature. Microstructural analysis of the prepared polymer using homodecoupled 1H NMR spectroscopy revealed the formation of a stereoblock architecture containing long isotactic sequence of R and S blocks in the main chain. A proposed mechanism involving chain-end control and stereoerror explains the stereoselective polymerization.