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Abstract:Synthesis of highly isotactic polylactide (PLA) via organocatalyzed stereoselective ring-opening polymerization (ROP) of racemic lactide (rac-LA) is a key strategy to improve the physico-chemical properties of PLA. In this context, the proton sponge bisphosphazene 1,8-bis(hexamethyltriaminophosphazenyl)naphthalene (HMPN) was synthesized and applied to catalyze the stereoselective ROP of rac-LA. Semicrystalline PLA with a P-m of 0.75 was conveniently prepared at room temperature. PLAs with higher tacticity (P-m up to 0.93) and higher melting temperature (T-m up to 189 degrees C) were obtained at lowered temperature. Binary catalysts composed of HMPN and ureas exhibited both high activity (99% monomer conversion within 5 minutes) and high stereoselectivity (Pm up to 0.83) at room temperature. In situ NMR study of HMPN, urea, and BnOH demonstrated the weak interactions between HMPN and BnOH, verifying the kinetic inactivity to deprotonation of HMPN. Kinetic studies verified the controlled manner and chain end control mechanism for the HMPN/U-2 catalyzed ROP of rac-LA.
Volume:15
Issue:21
Translation or Not:no