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Cation-pi Interactions accelerate the living cationic ring-opening polymerization of unsaturated 2-alkyl-2-oxazolines

Elias Van Den Broeck (UGent) , Bart Verbraeken (UGent) , Karen Dedecker (UGent) , Pieter Cnudde (UGent) , Louis Vanduyfhuys (UGent) , Toon Verstraelen (UGent) , Kristof Van Hecke (UGent) , Valentin-Victor Jerca (UGent) , Saron Catak (UGent) , Richard Hoogenboom (UGent) , et al.
(2020) MACROMOLECULES. 53(10). p.3832-3846
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Abstract
Cation-dipole interactions were previously shown to have a rate-enhancing effect on the cationic ring-opening polymerization (CROP) of 2-oxazolines bearing a side-chain ester functionality. In line with this, a similar rate enhancement-via intermolecular cation-pi interactions-was anticipated to occur when pi-bonds are introduced into the 2-oxazoline side-chains. Moreover, the incorporation of pi-bonds allows for facile postfunctionalization of the resulting poly(2-oxazoline)s with double and triple bonds in the side-chains via various click reactions. Herein, a combined molecular modeling and experimental approach was used to study the CROP reaction rates of 2-oxazolines with side-chains having varying degrees of unsaturation and side-chain length. The presence of cation-pi interactions and the influence of the degree of unsaturation were initially confirmed by means of regular molecular dynamics simulations on pentameric systems. Furthermore, a combination of enhanced molecular dynamics simulations, static calculations, and a thorough analysis of the noncovalent interactions was performed to unravel to what extent cation-pi interactions alter the reaction kinetics. Additionally, the observed trends were confirmed also in the presence of acetonitrile as solvent, in which experimentally the polymerization is performed. Most intriguingly, we found only a limited effect on the intrinsic reaction kinetics of the CROP and a preorganization effect in the reactive complex region. The latter effect was established by the unsaturated side-chains and the cationic center through a complex interplay between cation-pi, pi-pi, pi-induced dipole, and cation-dipole interactions. These findings led us to propose a two-step mechanism comprised of an equilibration step and a CROP reaction step. The influence of the degree of unsaturation, through a preorganization effect, on the equilibration step was determined with the following trend for the polymerization rates: n-ButylOx < ButenOx < ButynOx >= PentynOx. The trend was experimentally confirmed by determining the polymerization rate constants.
Keywords
FREE-RADICAL POLYMERIZATION, DENSITY-FUNCTIONAL THEORY, RATE, COEFFICIENTS, PROPAGATION RATE, SOLVENT, PREDICTION, POLY(2-OXAZOLINE)S, SIMULATIONS, COMPLEXES, CHEMISTRY

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MLA
Van Den Broeck, Elias, et al. “Cation-Pi Interactions Accelerate the Living Cationic Ring-Opening Polymerization of Unsaturated 2-Alkyl-2-Oxazolines.” MACROMOLECULES, vol. 53, no. 10, 2020, pp. 3832–46, doi:10.1021/acs.macromol.0c00865.
APA
Van Den Broeck, E., Verbraeken, B., Dedecker, K., Cnudde, P., Vanduyfhuys, L., Verstraelen, T., … Van Speybroeck, V. (2020). Cation-pi Interactions accelerate the living cationic ring-opening polymerization of unsaturated 2-alkyl-2-oxazolines. MACROMOLECULES, 53(10), 3832–3846. https://doi.org/10.1021/acs.macromol.0c00865
Chicago author-date
Van Den Broeck, Elias, Bart Verbraeken, Karen Dedecker, Pieter Cnudde, Louis Vanduyfhuys, Toon Verstraelen, Kristof Van Hecke, et al. 2020. “Cation-Pi Interactions Accelerate the Living Cationic Ring-Opening Polymerization of Unsaturated 2-Alkyl-2-Oxazolines.” MACROMOLECULES 53 (10): 3832–46. https://doi.org/10.1021/acs.macromol.0c00865.
Chicago author-date (all authors)
Van Den Broeck, Elias, Bart Verbraeken, Karen Dedecker, Pieter Cnudde, Louis Vanduyfhuys, Toon Verstraelen, Kristof Van Hecke, Valentin-Victor Jerca, Saron Catak, Richard Hoogenboom, and Veronique Van Speybroeck. 2020. “Cation-Pi Interactions Accelerate the Living Cationic Ring-Opening Polymerization of Unsaturated 2-Alkyl-2-Oxazolines.” MACROMOLECULES 53 (10): 3832–3846. doi:10.1021/acs.macromol.0c00865.
Vancouver
1.
Van Den Broeck E, Verbraeken B, Dedecker K, Cnudde P, Vanduyfhuys L, Verstraelen T, et al. Cation-pi Interactions accelerate the living cationic ring-opening polymerization of unsaturated 2-alkyl-2-oxazolines. MACROMOLECULES. 2020;53(10):3832–46.
IEEE
[1]
E. Van Den Broeck et al., “Cation-pi Interactions accelerate the living cationic ring-opening polymerization of unsaturated 2-alkyl-2-oxazolines,” MACROMOLECULES, vol. 53, no. 10, pp. 3832–3846, 2020.
@article{8666911,
  abstract     = {Cation-dipole interactions were previously shown to have a rate-enhancing effect on the cationic ring-opening polymerization (CROP) of 2-oxazolines bearing a side-chain ester functionality. In line with this, a similar rate enhancement-via intermolecular cation-pi interactions-was anticipated to occur when pi-bonds are introduced into the 2-oxazoline side-chains. Moreover, the incorporation of pi-bonds allows for facile postfunctionalization of the resulting poly(2-oxazoline)s with double and triple bonds in the side-chains via various click reactions. Herein, a combined molecular modeling and experimental approach was used to study the CROP reaction rates of 2-oxazolines with side-chains having varying degrees of unsaturation and side-chain length. The presence of cation-pi interactions and the influence of the degree of unsaturation were initially confirmed by means of regular molecular dynamics simulations on pentameric systems. Furthermore, a combination of enhanced molecular dynamics simulations, static calculations, and a thorough analysis of the noncovalent interactions was performed to unravel to what extent cation-pi interactions alter the reaction kinetics. Additionally, the observed trends were confirmed also in the presence of acetonitrile as solvent, in which experimentally the polymerization is performed. Most intriguingly, we found only a limited effect on the intrinsic reaction kinetics of the CROP and a preorganization effect in the reactive complex region. The latter effect was established by the unsaturated side-chains and the cationic center through a complex interplay between cation-pi, pi-pi, pi-induced dipole, and cation-dipole interactions. These findings led us to propose a two-step mechanism comprised of an equilibration step and a CROP reaction step. The influence of the degree of unsaturation, through a preorganization effect, on the equilibration step was determined with the following trend for the polymerization rates: n-ButylOx < ButenOx < ButynOx >= PentynOx. The trend was experimentally confirmed by determining the polymerization rate constants.},
  author       = {Van Den Broeck, Elias and Verbraeken, Bart and Dedecker, Karen and Cnudde, Pieter and Vanduyfhuys, Louis and Verstraelen, Toon and Van Hecke, Kristof and Jerca, Valentin-Victor and Catak, Saron and Hoogenboom, Richard and Van Speybroeck, Veronique},
  issn         = {0024-9297},
  journal      = {MACROMOLECULES},
  keywords     = {FREE-RADICAL POLYMERIZATION,DENSITY-FUNCTIONAL THEORY,RATE,COEFFICIENTS,PROPAGATION RATE,SOLVENT,PREDICTION,POLY(2-OXAZOLINE)S,SIMULATIONS,COMPLEXES,CHEMISTRY},
  language     = {eng},
  number       = {10},
  pages        = {3832--3846},
  title        = {Cation-pi Interactions accelerate the living cationic ring-opening polymerization of unsaturated 2-alkyl-2-oxazolines},
  url          = {http://dx.doi.org/10.1021/acs.macromol.0c00865},
  volume       = {53},
  year         = {2020},
}

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