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Carbocyclic-Fused Amino/iminopyridine-Iron Catalysts for Controlled Lactide Ring-Opening Polymerization
Summary
Scientists have developed new iron-based catalysts that help turn plant-based materials into biodegradable plastic (PLA) more efficiently, using a chemical process that wastes nothing. This matters because most plastics today don't break down and end up polluting our environment and bodies as microplastics, so finding better ways to make plastics that safely decompose could reduce our long-term exposure to plastic waste. The catalysts also use iron instead of rarer, more toxic metals, making this approach more practical and potentially safer to produce at scale.
High Resolution Image Download MS PowerPoint Slide Pervasive plastic pollution poses a critical threat to ecosystems, public health, and global economies, highlighting the need for biodegradable polymers synthesized with 100% atom economy. In this study, a series of carbocyclic-fused amino/iminopyridine-iron dichloride complexes, varying in coordination mode (bidentate and tridentate) and steric/electronic properties, were evaluated for the ring-opening polymerization of lactide. In the presence of propylene oxide as an activator, iron complexes bearing bidentate ligands exhibited superior and more controlled catalytic performance than tridentate complexes, reaching turnover frequencies as high as 186 h –1, whereas their tridentate counterparts produced polylactides with lower conversion and molecular weights. Modulation of the ligand structure exerted a pronounced influence on polymer characteristics, affording PLA with a number-average molecular mass of 4.8 × 10 3 to 13.5 × 10 3 g mol –1 and narrow dispersities ( Đ: 1.26–1.95). Especially, higher propylene oxide loadings enhanced catalytic activity at the expense of polymerization control, while a PO/Fe ratio of 300 resulted in slightly diminished conversion but improved molecular weight control. MALDI-TOF mass spectrometric analysis revealed polymer chains initiated through epoxide ring opening by chloride or trace moisture, producing end groups of −OCH(Me)CH 2 Cl/–OH or −OCH(Me)CH 2 OH/–OH.