V. Aviyente

Origins of the Solvent Effect on the Propagation Kinetics of Acrylic Acid and Methacrylic Acid

I. Değirmenci, T. Furuncuoğlu, O. Karahan, V. Van Speybroeck, M. Waroquier, V. Aviyente
Journal of Polymer Science Part A: Polymer Chemistry
51 (9), 2024–2034
2013
A1

Abstract 

In this study, the relative rate of polymerization of acrylic acid (AA) versus methacrylic acid (MAA) and the effect of water on the polymerization kinetics are investigated within a combined static and molecular dynamics set of computational tools. Experimentally the relative rate of propagation of AA versus MAA is around 35 in bulk and 31 in water. Classical Molecular Dynamics calculations have been carried out to determine the location of the solvent molecules in the proximity of the dimeric poly(AA) and poly(MAA) units. A combined implicit/explicit solvent model was used for the evaluation of the kinetics of the dimeric polymer chains. We show that the rate acceleration of both polymers in water is mainly due to entropic rather than electrostatic effects and is in agreement with experimental findings. Moreover the slower propagation rate of MAA versus AA is ascribed to additional steric effects present in MAA due to the methyl group at the α position of the monomer. Among the functionals used, the M06-2X/6-311+G(3df,2p)//B3LYP/6-31+G(d) methodology reproduces the experimental rate constants quantitatively the best. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

Solvent-Catalyzed Ring-Chain-Ring Tautomerization in Axially Chiral Compounds

A. Yıldırım, A. Konuklar, S. Catak, V. Van Speybroeck, M. Waroquier, I. Doğan, V. Aviyente
Chemistry - A European Journal
18 (40), 12725-12732
2012
A1

Abstract 

The mechanism of ring–chain–ring tautomerization and the prominent effect of the solvent environment have been computationally investigated in an effort to explain the enantiomeric interconversion observed in 2-oxazolidinone derivatives, heterocyclic analogues of biphenyl atropisomers, which were isolated as single stable enantiomers and have the potential to be used as axially chiral catalysts. This study has shed light on the identity of the intermediate species involved in the ring–chain–ring tautomerization process as well as the catalytic effect of polar protic solvents. These mechanistic details will prove very useful in predicting and understanding ring–chain tautomeric equilibria in similar heterocyclic systems and will further enable experimentalists to devise appropriate experimental conditions in which axially chiral catalysts remain stable as single enantiomers.

DFT Study on the Propagation Kinetics of Free-Radical Polymerization of α-Substituted Acrylates

I. Değirmenci, V. Aviyente, V. Van Speybroeck, M. Waroquier
Macromolecules
42 (8), 3033–3041
2009
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Abstract 

The kinetics of the free-radical propagation of methyl acrylate (MA), methyl methacrylate (MMA), ethyl α-fluoroacrylate (EFA), ethyl α-chloroacrylate (ECA), ethyl α-cyanoacrylate (ECNA), and methyl α-hydroxymethacrylate (MHMA) have been calculated using quantum chemical tools. Various DFT functionals such as BMK, BB1K, MPW1B95, MPW1K, and MPWB1K were used to model the relative propagation kinetics of the monomers. Among the methodologies used, MPWB1K/6-311+G(3df,2p)//B3LYP/6-31+G(d) was found to yield the best qualitative agreement with experiment. We explored chain length effects by examining addition reactions of monomeric, dimeric, trimeric, and tetrameric radicals to the monomers. We have also modeled the tacticity of the widely used monomers MA and MMA by considering all of the alternatives of attack of the radical in the 3D space around the monomer. This study has qualitatively confirmed the experimental syndiotactic/isotactic ratio of 66/3 for MMA. Finally, the kinetics of the initiation to polymerization for MA and MMA is also successfully reproduced.

Density Functional Theory Study of Free-Radical Polymerization of Acrylates and Methacrylates:  Structure−Reactivity Relationship

I. Değirmenci, D. Avci, V. Aviyente, K. Van Cauter, V. Van Speybroeck, G.B. Marin, M. Waroquier
Macromolecules
40 (26), 9590–9602
2007
A1

Abstract 

Radical polymerization processes occur through a complex network of many different reactions. It is well-known that the polymerization rate is directly related to the monomer structure. The experimental polymerizability behavior is expressed as kp/kt1/2, where kp is the rate coefficient of propagation and kt is the rate coefficient of termination. In this study, the reactivity of a series of acrylates and methacrylates is modeled in order to understand the effect of the pendant group size, the polarity of a pendant group, and the nature of the pendant group (linear vs cyclic) on their polymerizability. The geometries and frequencies are calculated with the B3LYP/6-31+G(d) methodology whereas the energetics and kinetics of these monomers have been studied using the two-component BMK/6-311+G(3df,2p)//B3LYP/6-31+G(d) level of theory. For rotations about forming/breaking bonds in the transition state, an uncoupled scheme for internal rotations has been applied with potentials determined at the B3LYP/6-31+G(d) level. Generally the rate constants for propagation kp mimic the qualitative polymerization trend of the monomers modeled and can be used with confidence in predicting the polymerizability behavior of acrylates. However in the case of 2-dimethylaminoethyl acrylate, chain transfer is found to play a major role in inhibiting the polymerization. On the other hand, the disproportionation reaction turns out to be too slow to be taken into consideration as a termination reaction.

Modeling the Solvent Effect on the Tacticity in the Free Radical Polymerization of Methyl Methacrylate

I. Değirmenci, S. Eren, V. Aviyente, B. De Sterck, K. Hemelsoet, V. Van Speybroeck, M. Waroquier
Macromolecules
43 (13), 5602–5610
2010
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Abstract 

The control of stereochemistry in the free radical polymerization of methyl methacrylate (MMA) is important because the physical properties of PMMA are often significantly affected by the main-chain tacticity. In this study, the role of the solvent on the tacticity of MMA polymerization has been investigated by considering the propagation rate constants for the syndiotactic and isotactic free radical polymerization of MMA in vacuum, in methanol (CH3OH), and in 1,1,1,3,3,3-hexafluoro-2-(trifluoromethyl)propan-2-ol ((CF3)3COH). All geometry optimizations have been carried out with the B3LYP/6-31+G(d) methodology. The kinetics of the propagating dimer have been evaluated with the B3LYP/6-31+G(d), B3LYP/6-311+G(3df,2p), MPWB1K/6-311+G(3df,2p), and B2PLYP/6-31+G(d) methodologies. The role of the solvent has been investigated by using explicit solvent molecules and also by introducing a polarizable continuum model (IEF-PCM) with a dielectric constant specific to the solvent. Experimentally, the free radical polymerization of MMA in (CF3)3COH is found to be highly syndiotactic (rr = 75% at 20 °C): the stereoeffects of fluoroalcohols are claimed to be due to the hydrogen-bonding interaction of the alcohols with the monomers and growing species. This modeling study has revealed the fact that the solvents CH3OH and (CF3)3COH, which are H-bonded with the carbonyl oxygens located on the same side of the backbone hinder the formation of the isotactic PMMA to some extent. Methanol is less effective in reducing the isotacticity because of its small size and also because of the relatively loose hydrogen bonds (1.9 Å) with the carbonyl oxygens. The methodologies used in this study reproduce the solvent effect on the free radical polymerization kinetics of MMA in a satisfactory way.

A Theoretical Study of the Mechanism of the Desymmetrization of Cyclic meso-Anhydrides by Chiral Amino Alcohols

B. Dedeoglu, S. Catak, K.N. Houk, V. Aviyente
ChemCatChem
2 (9), 1122-1129
2010
A1

Abstract 

The alcoholysis of cyclic meso-anhydrides catalyzed by β-amino alcohols has been investigated with DFT quantum mechanics to determine the mechanism of this reaction. Both nucleophilic catalysis and general base catalysis pathways are explored for methanol-induced ring opening of an anhydride catalyzed by a chiral amino alcohol. The nucleophilic pathway involves a late transition state with a high energy barrier. In this mechanism, methanolysis is expected to take place following the amine-induced ring opening of the anhydride. In the base-catalyzed mechanism, methanol attack on one carbonyl group of the meso-anhydride is assisted by the β-amino alcohol; the amine functionality abstracts the methanol proton. The chiral amino alcohol also catalyzes the reaction by stabilizing the oxyanion that forms upon ring opening of the anhydride by hydrogen bonding with its alcoholic moiety. Both stepwise and concerted pathways have been studied for the general base catalysis route. Transition structures for both are found to be lower in energy than in the nucleophilic mechanism. Overall this study has shed light on the mechanism of the β-amino alcohol-catalyzed alcoholysis of cyclic meso-anhydrides, showing that the nucleophilic pathway is approximately 100 kJ mol−1 higher in energy than the general base pathway.

Controlling the Tacticity in the Polymerization of N-Isopropylacrylamide: a computational study

T. Furuncuoğlu, I. Değirmenci, V. Aviyente, C. Atilgan, B. De Sterck, V. Van Speybroeck, M. Waroquier
Polymer
52 (24), 5503 - 5512
2011
A1

Abstract 

In this study, the effect of alcohols as solvents on the kinetics and the tacticity of poly(N-Isopropylacrylamide) (PNIPAM) is investigated with a combined static and molecular dynamics set of computational tools. Classical molecular dynamics calculations have been carried out to determine the location of the solvent molecules in the proximity of the monomer and the dimer. A combined implicit/explicit solvent model was used for the evaluation of the kinetics of the dimeric polymer chains. Rate constants are calculated with the B3LYP/6-311 + G(d,p)//B3LYP/6-31 + G(d), BMK/6-311 + G(d,p)//B3LYP/6-31 + G(d), and MPWB1K/6-311 + G(d,p)//B3LYP/6-31 + G(d) methodologies via the standard transition state theory. We show that due to the proximity of the –NH and carbonyl groups on the syndiotactic propagating dimeric and trimeric chains, the alcohol can stabilize the corresponding transition states by forming a bridge between these functionalities and accelerate this path more than its isotactic counterpart. In agreement with experiment, the increase in the syndiotactic PNIPAM and the acceleration of the reaction in the presence of t-BuOH is predicted with all the DFT functionals utilized in this study.

Modeling Ring-chain-ring Tautomerization of N-(o-aryl)-4-Hydroxy-2-oxazolidinone Derivatives

Abstract PII 141
Poster

Conference / event / venue 

Ninth Triennial Congress of the World Association of Theoretical and Computational Chemists (WATOC)
Santiago de Compostela, Spain
Sunday, 17 July, 2011 to Friday, 22 July, 2011

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