Thermodynamics transfer radical polymerization

Lin, C. Y., M. L. Coote, A. Gennaro, and K. Matyjaszewski. Ah initio evaluation of the thermodynamic and electrochemical properties of alkyl halides and radicals and their mechanistic implications for atom transfer radical polymerization. J. Am. Chem. Soc. 130, 2008 12762-1277. 

Braunecker WA, Tsarevsky NV, Gennaro A, Matyjaszewski K. Thermodynamic components of the atom transfer radical polymerization equilibrium quantifying solvent effects. Macromolecules 2009 42 6348-6360. 

DT relies on a thermodynamically neutral (degenerative) transfer reaction. The key for control is a minimal energy barrier for that reaction. Conventional free radical initiators are used, i.e., peroxides and diazenes, at temperatures typical for radical polymerization and the polymerization is carried out in the presence of a compound with a labile group or atom which can be either reversibly abstracted or added-fragmented by the growing radical. The simplest examples are reactions in the presence of alkyl iodides [33,183-184] Scheme 11 ... 

ESI mass spectrometry ive mass spectrometry ESR spectroscopy set EPR spectroscopy ethyl acetate, chain transfer to 295 ethyl acrylate (EA) polymerizalion, transfer constants, to macromonomers 307 ethyl methacrylate (EMA) polymerization combination v.v disproportionation 255, 262 kinetic parameters 219 tacticity, solvent effects 428 thermodynamics 215 ethyl radicals... 

The analysis of the reaction serum (the continuous phase without polymer particles) at the end of polymerization led to the conclusion that the molecular weight of the soluble oligomers of styrene and PEO macromonomer varied from 200 to 1100 g mol-1. This indicates that the critical degree of polymerization for precipitation of oligomers in this medium is more than ten styrene units and only one macromonomer unit per copolymer chain. Several reasons for the low molecular weight of the soluble copolymers were proposed, such as the thermodynamic repulsion (or compatibility) between the PEO chain of the macromonomer and the polystyrene macroradical, the occurrence of enhanced termination caused by high radical concentration, and, to a lower extent, a transfer reaction to ethanol [75]. 

A certain kind of radical transfer can be modelled by the transfer of a hydrogen atom from an alkane molecule to a small alkyl radical. This reaction was studied in detail in the gas phase. With hydrocarbon partners, heats of reaction are a fairly safe measure of the relative rate of transfer, as the pre-exponential Arrhenius factors remain approximately constant for a series of transfers to a given radical. Tabulated thermodynamic data indicate, however, [31, 32] that the correlation between the heat of reaction and the transfer rate is not valid for reactions of a radical with polar substrates [32, 33], In condensed phases, transfer reactions have not been sufficiently studied. Polymerizations themselves are the source of the most valuable, though incomplete, information. 

A similar study performed for CQ-NPG initiator systems [175] showed a rather different kinetic behavior (Figure 35). The rate of polymerization is reduced when the thermodynamic driving force (-ACet) of the process is increased, and this demonstrates inverted-region-like kinetic behavior. The authors explained this variation in reactivity as due to the reactivity of the free radicals formed as a result of processes occurring after electron transfer [123]. 

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