Molecular Aspects of Radical Polymerizations—The Propagation Frequency

Abstract

The product of the propagation rate constant and monomer concentration is a central issue of radical polymerization. Both quantities are strongly interrelated as the determination of a reliable value of the propagation rate constant requires exact knowledge of the monomer concentration. Even for homogeneous polymerization conditions, exact knowledge of the monomer concentration at the reaction site from the molecular perspective is not trivial. For emulsion polymerizations the situation is additionally complicated by mass transfer events and colloid-chemical effects. Molecular modeling appears as an attractive alternative or complement to the deterministic kinetic description of radical polymerizations.

Effects of stirring prior to starting emulsion polymerization of styrene with nonionic emulsifier on particle formation and its incorporation

“…6, styrene concentration inside particles decreased monotonuously with increasing conversion. This is in accord with that recently reported by Tauer and Hernangez, theoretically and experimentally, that monomer concentration inside particles, [M] P , decreases over the whole emulsion polymerization [14],although in emulsion polymerization, it is well known that there is an interval at which [M] P is constant, within the frame of the Smith-Evart theory (Interval II). Because this subject is not the main topic in this paper, it will be discussed elsewhere in a future.…”

Molecular Versus Conventional Kinetics of Emulsion Polymerization

“…There are other experimental facts and theoretical arguments supporting the necessity of changing the view on swelling 22. It turned out that the knowledge of the physical state of the monomer in the reaction system is extremely helpful, not only for swelling but for better understanding of emulsion polymerization in general 22–24. The images of Figure 7 give a glimpse about the real situation and illustrate essential features.…”

“…Because some of these processes cannot be investigated independently, the conventional approach to determine the kinetics of emulsion polymerization relies on many kinetic model assumptions followed by the identification of the model parameters from experimental data 25. One the other hand, the development of powerful and reliable techniques for the simulation of the behavior of atoms and molecules has allowed the determination of the kinetics of individual, completely independent processes in emulsion polymerization 22, 26, 27. The main advantage of this new approach is the precise control of the “experimental” conditions, which allows the identification of the true effect of individual phenomena on the reaction kinetics.…”

“…A multiscale modeling approach may consist in the determination of monomer absorption and desorption rates by means of Brownian Dynamics simulation, followed by the simulation of the consumption of monomer by propagation either inside the particles or in the continuous phase. As a result of this multiscale approach, it is possible to determine the change in polymer particle size during emulsion polymerization under any particular conditions 22. The results obtained describe very precisely the behavior observed experimentally by different researchers, demonstrating the potential of multiscale molecular modeling for simulating in detail an emulsion polymerization process.…”

High-Temperature Cross-Linking of Carbon Nanotube Multi-Yarn Using Polyvinylpyrrolidone as a Binding Agent

“…This is also expected, since the polymerization theory predicts that the rate of polymerization is proportional to monomer concentration. 24 The PVP monomers that did not become part of a polymer chain were washed away. Therefore, more polymerization corresponds with a greater increase in linear mass density.…”