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Reaction Environment Effect on the Kinetics of Radical Thiol–Ene Polymerizations in the Presence of Amines and Thiolate Anions
journal contribution
posted on 2020-01-16, 13:06 authored by Dillon Love, Benjamin Fairbanks, Christopher BowmanBecause
of facile implementation, quantitative conversions, and an insensitivity
to oxygen, water, and most organic functional groups, radical-mediated
thiol–ene coupling (TEC) reactions have emerged as a valuable
tool in macromolecule synthesis. It was recently demonstrated that
the kinetics and conversions of thiyl radical-mediated reactions are
adversely affected in the presence of basic amines by the formation
of retardive thiolate anions. Herein, the performance of TEC polymerizations
is evaluated under a variety of reaction environments with the intention
to aid in the optimal formulation design of TEC reactions in the presence
of amines. Results from both bulk and aqueous-phase network photopolymerizations
established that sensitivity to amine basicity and pH is dependent
on the thiol acidity, although norbornene-type alkenes exhibit a unique
ability to achieve high conversions, where allyl ethers, vinyl ether,
and vinyl siloxanes are highly inhibited. Additionally, the protic
solvents such as alcohols and acetic acid are established as ideal
solvents or additives to suppress or eliminate amine-induced retardation.
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norbornene-type alkenes exhibitThiolate Anionsvinyl etheracetic acidretardive thiolate anionsthiyl radical-mediated reactionsTEC reactionsformulation designReaction Environment Effectprotic solventsTEC polymerizationsthiol aciditypresenceamine-induced retardationaminesamine basicitymacromolecule synthesisreaction environmentsvinyl siloxanesallyl ethersconversionaqueous-phase network photopolymerizations
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