Addition-Fragmentation Kinetics of Fluorodithioformates (F-RAFT) in Styrene, Vinyl Acetate, and Ethylene Polymerization: An Ab Initio Investigation

Predicting Entropic Effects of Water Mixing with Ionic Liquids Containing Anions of Strong Hydrogen Bonding Ability: Role of the Cation

Ionic liquids (ILs) such as choline dihydrogen phosphate exhibit an extraordinary solubilizing ability for proteins such as cytochrome C when mixed with 20 wt % water. Most widely used imidazolium-based ionic liquids coupled with dihydrogen phosphate do not exhibit the same solubilizing properties, suggesting that a multifunctional cation such as choline might play a key role in enhancing these properties of ionic liquid mixtures with water. In this theoretical work, we compare intermolecular interactions between the water molecule and ionic liquid ions in two ion-paired clusters of choline- and 1-butyl-3-methyl-imidazolium-based ionic liquids coupled with acetate, dihydrogen phosphate, and mesylate. Gibbs free energy (GFE) of solvation of water in these ionic liquids was calculated. Incorporation of a water molecule into ionic liquid clusters was accompanied by negative GFEs of solvation in both types of cations. These results were in good agreement with previously reported experimental GFEs of solvation of water in ILs. Compared to imidazolium-based clusters, strong interionic interactions of choline ionic liquids resulted in more negative GFEs due to their smaller deformation upon the addition of a water molecule, with dihydrogen phosphate and mesylate predicting the lowest GFEs of -30.1 and -43.5 kJ/mol^-1, respectively. Lower GFEs of solvation of water in choline-based clusters were also accompanied with smaller entropic penalties, suggesting that water easily incorporates itself into the existing ionic network. Analysis of the intramolecular bonds within the water molecule showed that the choline hydroxyl group donates electron density to the neighboring water molecule, leading to additional polarization. The predicted infrared spectra of clusters of ionic liquids with water showed a pronounced red shift due to strongly polarized O-H bonds, in excellent agreement with the experimentally measured infrared spectra of ionic liquid mixtures with water. Increased polarization of water in choline-based ionic liquids undoubtedly creates more effective solvents for stabilizing biological molecules such as proteins.

Dithiocarbamate RAFT agents with broad applicability – the 3,5-dimethyl-1H-pyrazole-1-carbodithioates

The RAFT agents offerĐ< 1.1 for MAMs, methyl acrylate (MA),N,N-dimethylacrylamide (DMA) and styrene, andĐ< 1.3 for LAMs, vinyl acetate (VAc); versatility and end-group fidelity was proved with synthesis both polyDMA-block-polyMA and polyDMA-block-polyVAc.

Fundamentals of RAFT Polymerization

This chapter sets out to describe the fundamental aspects of radical polymerization with reversible addition-fragmentation chain transfer (RAFT polymerization). Following a description of the mechanism we describe aspects of the kinetics of RAFT polymerization, how to select a RAFT agent to achieve optimal control over polymer molecular weight, composition and architecture, and how to avoid side reactions which might lead to retardation or inhibition.

2-[(Methoxycarbonothioyl)sulfanyl]acetic acid

The title compound, C₄H₆O₃S₂, features a characteristic xanthate group; the C=S double bond is shorter than the C—S single bond, and the methyl group is coplanar with the xanthate group. In the crystal pairs of mol­ecules form dimers through inter­molecular O—H⋯O hydrogen bonding.

RAFT Chemistry and Huisgen 1,3-Dipolar Cycloaddition: A Route to Block Copolymers of Vinyl Acetate and 6-O-Methacryloyl Mannose?

The present communication explores a novel avenue to glycopolymer-block-poly(vinyl acetate) polymers by a combination of reversible addition fragmentation chain transfer (RAFT) chemistry and Huisgen 1,3-dipolar cycloaddition (i.e., so-called ‘click’ chemistry) under mild reaction conditions. Such block copolymers are—because of the strongly disparate reactivity of the two monomers—otherwise not obtainable. Poly(vinyl acetate) that has an azide end group (Mn 6800 g mol–1, PDI 1.15) was treated with poly(6-O-methacryloyl mannose) (Mn 7600 g mol–1, PDI 1.11) in the presence of 1,8-diaza[5,4,0]bicycloundec-7-ene and copper(i) iodide. The resulting poly(vinyl acetate)-block-poly(6-O-methacryloyl mannose) had a number-average molecular weight of 15400 g mol–1 and a PDI of 1.48, which indicates that while the cycloaddition had occurred the resulting polymer distribution featured a considerable width. The resulting slightly amphiphilic block copolymer was subsequently investigated with regard to its self-assembly in aqueous solution. Dynamic light scattering studies indicated a hydrodynamic diameter of close to 200 nm. Transmission electron microscopy studies indicate the formation of rods as well as spheres with transitions between these two phases. However, the segregation between core and shell in the spheres is not pronounced; such behaviour is expected for weakly amphiphilic block copolymers.

The Use of Novel F-RAFT Agents in High Temperature and High Pressure Ethene Polymerization: Can Control be Achieved?

Simulations are employed to establish the feasibility of achieving controlled/living ethene polymerizations. Such simulations indicate that reversible addition–fragmentation chain transfer (RAFT) agents carrying a fluorine Z group may be suitable to establish control in high-pressure high-temperature ethene polymerizations. Based on these simulations, specific fluorine (F-RAFT) agents have been designed and tested. The initial results are promising and indicate that it may indeed be possible to achieve molecular weight distributions with a polydispersity being significantly lower than that observed in the conventional free radical process. In our initial trials presented here (using the F-RAFT agent isopropylfluorodithioformate), a correlation between the degree of polymerization and conversion can indeed be observed. Both the lowered polydispersity and the linear correlation between molecular weight and conversion indicate that control may in principle be possible.

Respective Contributions of Polar vs Enthalpy Effects in the Addition/Fragmentation of Mercaptobenzoxazole-Derived Thiyl Radicals and Analogues to Double Bonds

The formation and the reactivity of three selected sulfur-centered radicals formed from mercaptobenzoxazole, mercaptobenzimidazole, and mercaptobenzothiazole toward four double bonds (methyl acrylate, acrylonitrile, vinyl ether, and vinyl acetate) are investigated. The reversibility of the addition/fragmentation reaction in these widely used photoinitiating systems of radical polymerization was studied, for the first time, through the measurement of the corresponding rate constants by time-resolved laser spectroscopy. The combination of these results with quantum mechanical calculations clearly evidences that, contrary to previous studies on other aryl thiyl radicals, the addition rate constants (ka) are governed here by the polar effects associated with the very high electrophilic character of these radicals. However, interestingly, the back-fragmentation reaction (k-a) is mainly influenced by the enthalpy effects as supported by the relationship between the rate constants and the addition reaction enthalpy DeltaHR. The addition and fragmentation rate constants calculated from the transition state theory (TST) are in satisfactory agreement with the experimental ones. Therefore, molecular orbital (MO) calculations offered new opportunities for a better understanding of the sulfur-centered radical reactivity.

Ab Initio Kinetic Modelling in Radical Polymerization: A Paradigm Shift in Reaction Kinetic Analysis

We describe a new rationale to kinetic modelling in which adjustable parameters are avoided through the use of quantum chemistry. This new approach reverses the standard modelling approach in which, having first assumed a kinetic model, it is then fitted to the experimentally determined values of the macroscopic properties (rates, compositions, molecular weight distributions, and so forth) so as to estimate the rate coefficients of the individual reactions. Instead, one still assumes a reaction scheme, but then calculates the rates of the individual reactions using high-level ab initio calculations, and in this way a kinetic model is built that can be used to predict the macroscopic properties of the process from first principles. These can then be compared directly with experiment (for benchmarking purposes) and subsequently be employed to predict the outcome of new chemical processes. In here we illustrate the ab initio modelling technique, using a recent study of initialization in RAFT polymerization as a case study. We also discuss its advantages and possible problems, and highlight some of its potential applications in the radical polymer field.

Living Radical Polymerization by the RAFT Process—A First Update

This paper provides a first update to the review of living radical polymerization achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of Reversible Addition–Fragmentation chain Transfer (RAFT) published in June 2005. The time since that publication has witnessed an increased rate of publication on the topic with the appearance of well over 200 papers covering various aspects of RAFT polymerization ranging over reagent synthesis and properties, kinetics, and mechanism of polymerization, novel polymer syntheses, and diverse applications.

RAFT and click chemistry: A versatile approach to well-defined block copolymers

The combination of reversible chain transfer chemistry with highly orthogonal [2 + 3] cycloadditions ('click chemistry') allows for the synthesis of well-defined block copolymers of monomers with extremely disparate reactivities.