Stereocomplexed three-arm PPO–PDLA–PLLA copolymers: Synthesis via an end-functionalized initiator

• A novel stereoblock poly (lactic acid) with high molecular weight was synthesized initiated by end-functionalized PLAs.
• Three-arm stereoblock PLA has equivalent D-LA/L-LA compositions and high stereoregularity.
• Three-arm stereoblock PLA showed exclusive stereocomplex-crystallization behavior with a melting temperature about 207 °C.

Three-arm poly (propylene oxide)-block-poly (d-lactic acid) (PPO–PDLA) copolymers were successfully synthesized by ring-opening polymerization (ROP) of d-lactide using three-arm poly (propylene oxide) as a macroinitiator. PPO–PDLA copolymers were then functionalized with three ending tin (II)-alkoxide groups, and those functionalized copolymers could act as efficient initiators in polymerization of l-lactide at relative low temperature. The combination of proton nuclear magnetic resonance spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometer supported their structures of ending tin (II)-alkoxide groups. A series of novel three-arm poly (propylene oxide)-block-poly (d-lactic acid)-block-poly (l-lactic acid) (PPO–PDLA–PLLA) copolymers with high molecular weight (Mn > 2.0 × 105) and equivalent D-LA/L-LA compositions, were synthesized using those functionalized initiators in polymerization of l-lactide at 130 °C. The results show that PPO–PDLA–PLLA copolymers are highly stereoregularity, and the molecular weight of enantiomeric block reaches up to 8.0 × 104. Those three-arm PPO–PDLA–PLLA copolymers exhibit exclusive stereocomplex crystallization behavior with a high melting temperature about 207 °C.

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