Organocatalytic stereoselective ring-opening polymerization of lactide with dimeric phosphazene bases

Highly isotactic polylactide with a high melting temperature was synthesized from rac-lacticle through an organocatalytic route using dimeric phosphazene base 1-tert -butyl-2,2,4,4,4-pentakis(dimethylamino)-2 Delta(5),4 Delta(5)-catenadi(phosphazene) (P-2-t -Bu) catalyst at low temperature. Microstructural analysis of the prepared polymer using homodecoupled H-1 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.