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H‑Bonding Organocatalysts for Ring-Opening Polymerization at Elevated Temperatures
journal contribution
posted on 2018-12-11, 21:46 authored by Danielle
N. Coderre, Kurt V. Fastnacht, Thomas J. Wright, Nayanthara U. Dharmaratne, Matthew K. KiesewetterThe 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.
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Keywords
reaction conditionsEyring behaviorsolution polarity changesamine cocatalystring-opening polymerizationbis-urea H-bond donorconversionH-bonding organocatalystsε- caprolactonebase cocatalystimidate formcocatalyst systems exhibit decompositionROPcocatalyst systemsonset temperaturecocatalyst decompositionElevated TemperaturesthioActivation parametersRing-Opening Polymerization
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