H‑Bonding Organocatalysts for Ring-Opening Polymerization at Elevated Temperatures Danielle N. Coderre Kurt V. Fastnacht Thomas J. Wright Nayanthara U. Dharmaratne Matthew K. Kiesewetter 10.1021/acs.macromol.8b02219.s001 https://acs.figshare.com/articles/journal_contribution/H_Bonding_Organocatalysts_for_Ring-Opening_Polymerization_at_Elevated_Temperatures/7451147 The ring-opening polymerization (ROP) kinetics of ε-caprolactone and lactide with various H-bonding organocatalysts, (thio)­ureas paired with an amine cocatalyst, were evaluated at temperatures up to 110 °C. In nonpolar solvent, most cocatalyst systems exhibit decomposition at high temperatures, while only two, a monourea and bis-urea H-bond donor plus base cocatalyst, are stable up to 110 °C. The onset temperature of cocatalyst decomposition must be measured under reaction conditions. In polar solvent, when the more active imidate form of the (thio)­urea is favored, most cocatalyst systems become thermally stable up to 110 °C, exhibiting linear Eyring behavior, including some that were unstable in toluene. The very progress of an ROP is shown to influence the nature of the catalysts as the solution polarity changes from highly polar (at 0% conversion) to less polar at full conversion. Activation parameters are discussed, and a mechanistic explanation of the observations is proposed. 2018-12-11 21:46:49 reaction conditions Eyring behavior solution polarity changes amine cocatalyst ring-opening polymerization bis-urea H-bond donor conversion H-bonding organocatalysts ε- caprolactone base cocatalyst imidate form cocatalyst systems exhibit decomposition ROP cocatalyst systems onset temperature cocatalyst decomposition Elevated Temperatures thio Activation parameters Ring-Opening Polymerization