4.8 Article

An Air Stable Cationic Indium Catalyst for Formation of High-Molecular-Weight Cyclic Poly(lactic acid)

Journal

ACS CATALYSIS
Volume -, Issue -, Pages -

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acscatal.2c02118

Keywords

indium; cyclic; polylactide; cationic; air-stable; catalysis; molecular weight

Funding

  1. Natural Sciences and Engineering Research Council of Canada
  2. UBC Department of Chemistry
  3. UBC Chemistry Award for Graduate Research Excellence

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The synthesis of high-molecular-weight cyclic poly(lactide) (c-PLA) has been a challenge due to entropic constraints. This study successfully produced c-PLA with low dispersity and high molecular weights using an air-stable cationic alkyl indium complex. The complex remained active even after prolonged exposure to high-humidity air, allowing the formation of high-molecular-weight c-PLLA, c-PDLA, and their stereo-complex without epimerization.
Overcoming entropic constraints to selectively produce high-molecular-weight cyclic poly(lactide) (c-PLA) is a challenge. In this work, we use an air-stable cationic alkyl indium complex featuring a hemilabile pyridine pedant arm to reproducibly synthesize c-PLA exclusively with low dispersity (D) similar to 1.30) and high molecular weights (up to 416,000 g mol(-1)). The complex remains active after extended periods of exposure to high-humidity air. The process allows the formation of high-molecular-weight c-PLLA, c-PDLA, and their stereo-complex with no epimerization. We propose that polymerization occurs through a cooperative Lewis-pair-based coordination-insertion mecha-nism where the monomer coordination to the cationic indium center and ring-opening of lactide by the hemilabile pyridine donor group are essential steps.

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