Some Representative Experimental Data of Particle Nucleation

2 Some Representative Experimental Data of Particle Nucleation 

Sahoo and Mohapatra [66] studied the catalytic effect of the in situ developed Cu(II)-EDTA complex with ammonium persulfate on the surfactant-free emulsionpolymerization of methyl methacrylate. The rate ofpolymerization at 50 °C is proportional to the concentrations of Cu(II), EDTA, ammonium persulfate, and methyl methacrylate to the 0.35, 0.69, 0.57, and 0.75 powers, respectively. In addition, the apparent activation energy and activation energies of the initiator decomposition, propagation, and termination reactions, respectively, are 34.5,26.9,29, and 16 kJ mol. It was proposed that the complex just acts as an effective surfactant in stabilizing the polymethyl methacrylate nanoparticles nucleated during polymerization. Independent experiments are required to verify this speculation and clarify the related stabilization mechanism. 

Sutterlin [46] studied the effect of the polarity of various monomers (styrene, acrylate ester monomers, and methacrylate ester monomers see Table 3.1) on the particle nucleation mechanisms involved in emulsion polymerization. When the surfactant concentration is above its CMC, the emulsion polymerization of styrene follows the Smith-Ewart theory (Npj 5o ) except those experiments with relatively low levels of surfactant. The exponent x in the relationship Npj So decreases with increasing monomer polarity when the surfactant concentration is above its CMC. This trend is attributed to the increased tendency of agglomeration of particle nuclei with monomer polarity. The emulsion polymerizations of less polar monomers deviate significantly from the Smith-Ewart theory (x 0.6) if the surfactant concentration is reduced to a level just below its CMC. This implies that some mechanisms other than micellar nucleation (homogeneous nucleation or coagulative nucleation) must operate in these emulsion polymerization systems. 

Varela de la Rosa et al. [68-70] carried out emulsion polymerizations of styrene stabilized by sodium dodecyl sulfate and initiated by potassium persulfate at 50 °C. They proposed the following reaction mechanism to describe the conventional styrene emulsion polymerization system. 

Micellar nucleation is the predominant mechanism, and monomer-swollen micelles disappear in the monomer conversion range of 5-10%, which marks the end of Stage I. 

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