Bisurea and Bisthiourea H-Bonding Organocatalysts for Ring-Opening Polymerization: Cues for the Catalyst Design
Document Type
Article
Date of Original Version
12-10-2019
Abstract
A series of conformationally flexible bis(thio)urea H-bond donors plus base cocatalyst were applied to the ring-opening polymerization (ROP) of lactones. The rate of the ROP displays a strong dependence on the length and identity of the tether, where a circa five methylene-unit long tether exhibits the fastest ROP. Any constriction to conformational freedom is deleterious to catalysis. For the ROP of δ-valerolactone (VL) and ϵ-caprolactone (CL), the bisurea H-bond donors are more effective, but for lactide, the bisthioureas are more active catalysts. The ROP reactions are rapid and controlled across a wide range of reaction conditions, including solvent-free conditions, exhibiting excellent weight control from low Mn to high polymers. The active mechanism is highly dependent on the identity of the base cocatalyst, and a mechanistic rationale for the observations is discussed. Implications for the design of future generation catalysts are discussed.
Publication Title, e.g., Journal
Macromolecules
Volume
52
Issue
23
Citation/Publisher Attribution
Hewawasam, Rukshika S., U. L. D. I. Kalana, Nayanthara U. Dharmaratne, Thomas J. Wright, Timothy J. Bannin, Elizabeth T. Kiesewetter, and Matthew K. Kiesewetter. "Bisurea and Bisthiourea H-Bonding Organocatalysts for Ring-Opening Polymerization: Cues for the Catalyst Design." Macromolecules 52, 23 (2019): 9232-9237. doi: 10.1021/acs.macromol.9b01875.