Adaption of the Mechanism of Emulsion Polymerization to New Experimental Results

Abstract

Summary: New experimental investigations of the 'classical' batch ab-initio emulsion polymerization of styrene reveal the important role of monomer droplets for the whole process. Monomer droplets with a size between a few and some hundreds of nanometers, which are formed by spontaneous emulsification as soon as styrene and water are brought into contact, have a strong influence on the particle nucleation, the particle morphology, and the swelling of the particles. Experimental results confirm that micelles of low molecular weight surfactants are not a major locus of particle nucleation. Brownian dynamics simulations show that the capture of matter by the particles (monomer or radicals) strongly depends on the polymer volume fraction and the size of the captured species (primary free radicals, oligomers, single monomer molecules, or clusters).

Molecular Aspects of Radical Polymerizations—The Propagation Frequency

“…[97,98] The consequences of these experimental findings for heterophase polymerizations are enormous regarding particle nucleation during ab initio polymerizations but also with respect to modification of latex particles as recently discussed. [99,100] The kinetics of the initial polymerization in the aqueous phase, that is, the duration of the pre-nucleation period and the particle nucleation kinetics, are strongly influenced by both the concentration and the state of the monomer concentration in the continuous phase.…”

A Surfactant-Free and Shape-Controlled Synthesis of Nonspherical Janus Particles with Thermally Tunable Amphiphilicity

“…Earlier works have reported that nonionic and hydrophobic initiators (e.g., AIBN) play a similar role with KPS in surfactant‐free suspension polymerization systems . When the initiators are dissociated into radical compounds in water, the conductivity of aqueous solutions increased, probably because the radicals created ionic species in water.…”

Molecular Versus Conventional Kinetics of Emulsion Polymerization

“…This observation strongly suggests that the energy barrier is connected with the event of particle nucleation. Indeed, non‐micellar nucleation theory, such as classical nucleation theory, that can also be applied for emulsion polymerization10–12 predicts that the rate of nucleation (r nuc ) is an exponential function (Equation 2) of the cube of the interfacial tension nucleus – water ( σ ), the molar volume of the nucleating species squared, the cube of the thermal energy (k B T), and the supersaturation (S) squared. …”