An Air Stable Cationic Indium Catalyst for Formation of High-Molecular-Weight Cyclic Poly(lactic acid)
Chatura Goonesinghe, Hyuk‐Joon Jung, Hootan Roshandel, Carlos Diaz, Hassan A. Baalbaki, Kudzanai Nyamayaro, Maria B. Ezhova, Kimia Hosseini, Parisa Mehrkhodavandi
Abstract
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 (Đ ∼ 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 stereocomplex with no epimerization. We propose that polymerization occurs through a cooperative Lewis-pair-based coordination–insertion mechanism where the monomer coordination to the cationic indium center and ring-opening of lactide by the hemilabile pyridine donor group are essential steps.