Dependence of Propagation Rate Coefficients in Radical Polymerization on Solution Properties

Abstract

The effect of solvents and monomer concentration on rate coefficients of propagation in radical polymerization has received tremendous interest during recent years, but a quantitative explanation and method of prediction of the medium effect is still missing. In this paper, it is shown that the thermodynamic formulation of the transition state theory is able to explain such effects almost quantitatively for a wide variety of monomers and solvents, including not only organic solvents but also less common solvents like ionic liquids or water, and monomers ranging from styrene to water‐soluble monomers like acrylic acid or N‐vinylformamide and also bulky monomers like isobornyl methacrylate. The medium effect is dictated by the activity coefficient of the monomer as well as by the ratio of the activity coefficients of the growing chain and the transition state. The solvent and concentration effects are, thus, a consequence of the degree of nonideality of the system. This interpretation based on the thermodynamics of real solutions offers for the first time a straightforward method to estimate the propagation rate coefficient of a given monomer in various solvents once the corresponding coefficient in bulk monomer is known.

Propagation Kinetics of Isoprene Radical Homopolymerization Derived from Pulsed Laser Initiated Polymerizations

“…Finally, the impact of a solvent on isoprene k p was investigated, because it is well known that organic solvents may affect k p in radical polymerizations 41,42. The majority of investigations into the solvent influence on k p referred to acrylate and methacrylate type monomers.…”

“…The majority of investigations into the solvent influence on k p referred to acrylate and methacrylate type monomers. The strongest solvent influences were reported for water, ionic liquids, or organic solvents such as DMSO, benzyl alcohol, or N ‐methyl pyrrolidinone 41,42. If monomer and solvent are rather similar, and if the solvent is a good solvent for the polymer, the solvent influence on k p is modest.…”

“…For a detailed discussion of this aspect, the reader is referred to the original literature 35,43,45–47. For the IP/DMAc system, non‐ideal mixing and the occurrence of local monomer concentrations or the need for using activities42 rather than concentrations is also suggested to be the origin of the apparent lowering of k p . A detailed investigation into the origin of the rather small variations in k p is beyond the scope of the manuscript.…”

“…Thus, the local isoprene concentration in the vicinity of the chain end may be slightly higher than the overall monomer concentration. In principle, the data can be discussed in terms of the publication by Deglmann et al,42 who proposed to used activities rather than local monomer concentrations. The concept comprises using two terms, a combinatorial term accounting for the molar volumes of monomer, solvent, and transition state structure, and a residual term accounting for enthalpic and entropic contributions.…”

“…The concept comprises using two terms, a combinatorial term accounting for the molar volumes of monomer, solvent, and transition state structure, and a residual term accounting for enthalpic and entropic contributions. However, due to the rather small DMAc influence on IP k p , due to lack of data for the molar volumes of the solvent at PLP conditions and the fact that the temperature dependence of the solvent influence was not investigated, we refrained from a detailed analysis according to the concept of Deglmann et al42…”