Miniemulsion polymerization of styrene: Evolution of the particle size distribution

Abstract

The mechanism of the miniemulsion polymerization of styrene was investiaged through a combination of calorimetry to monitor the polymerization rate and transmission electron microscopy (TEM) to follow the evolution of the particle size distribution. These techniques proved to be a powerful combination for gaining detailed mechanistic information regarding these polymerizations. Particle size analysis of the latexes withdrawn during the course of the reaction revealed that most of the polymer particles were formed by a relatively low conversion (i.e., 10% conversion). However, nucleation continued well past this point (to 40‐60% conversion). In fact, it was observed that nucleation in miniemulsion polymerizations using cetyl alcohol continued past the maximum in the rate of polymerization. As a result of these long nucleation periods, the latex particle size distributions produced from these miniemulsion polymerizations were broader than their conventional emulsion polymerization counterparts, and were negatively skewed with a tail of small particles. The amount of negative skewing of the particle size distributions was found to decrease with increasing initiator (potassium persulfate) concentration. Finally, a correlation was observed between the length of time to the maximum polymerization rate and the breadth of the particle size distribution as reflected in the standard deviation. © 1995 John Wiley & Sons, Inc.

Miniemulsion copolymerization of styrene and butyl acrylate initiated by redox system at lower temperature: Reaction kinetics and evolution of particle-size distribution

“…It can be seen that the particle-size distribution is broader at the beginning of the polymerization and becomes narrower as the polymerization proceeds. At the end of the polymerization, monodisperse polymer particles were obtained, while Miller et al 29 reported from the miniemulsion polymerization of St that the particle-size distribution is narrower at the beginning of the polymerizations and generally becomes broader as the polymerization proceeds.…”

“…Miller et al 29 studied in detail the evolution of the number of particles as a function of the fractional conversion for the different initiator concentrations studied. Their results suggested that the conversion at which nucleation ceases is determined to be between 40 and 60% conversion.…”

Sterically Stabilized Emulsion Polymerization of Styrene

“…36 The data in Table I, however, differ from those reported for the electrosterically stabilized emulsion polymerization of styrene where the desorption of radicals was depressed. [8][9][10] The decreased desorption of radicals was attributed to the thick emulsifier layer formed by the graft copolymer at the polymer particle surface. This difference between the present data and the literature ones might result from the difference in the solubility, the molecular weight and mobility of the stabilizers used.…”

“…This may not be a case for the high molecular weight copolymer. [8][9][10] The reduction in the polymerization rate with increasing the weight ratio of emulsifier and monomer can arise from the breakdown in the extent of compartmentalization of the free radicals in the latex particles and the increased exit of radicals. The decreased extent of compartmentalization of radicals is accompanied with the shapes of the conversion and polymerization rate curves (Figures 1 and 2) typical for the microemulsion polymerization characterized by the strong radical desorption.…”

“…For example, the electrosterically-stabilized latexes show somewhat smaller values of both entry (k a ) and exit (k des ) rate coefficients as compared to the electrostatically-stabilized latex particles of the same size. [8][9][10] The decreased k a or k des in the sterically-stabilized latexes is ascribed to a ''hairy'' layer around the particles, which retards diffusion of oligomeric radicals. The entering radicals may be terminated prior to the actual entry into the latex particles occurs.…”