A Kinetic Investigation of Surfactant-Free Emulsion Polymerization of Styrene Using Laponite Clay Platelets as Stabilizers

We report the kinetics and mechanism of soap-free emulsion polymerization of styrene using laponite platelets as stabilizers. The polymerization was initiated by potassium persulfate and the latex particles were stabilized by laponite platelets dispersed in water. Laponite adsorption on the polymer particles was enhanced by the addition of poly(ethylene glycol) monomethylether methacrylate (PEGMA). Particle nucleation can be described using the classical homogeneous nucleation mechanism followed by coagulation of unstable precursors. Oligomeric radicals formed in the water phase become insoluble and precipitate on the laponite surface leading to primary precursor particles composed of a few polymer chains and one or several clay platelets. Mature latex particles are then generated by coagulation and growth of the previously formed precursor particles. Both the nucleation and initial aggregation rates increased in the presence of PEGMA. Calorimetric monitoring of the polymerization allowed estimating the heat produced by the reaction and the monomer conversion. Hence, using the monomer material balance, the number of radicals in the polymer particles could be estimated precisely. The average number of radicals per particle, (n) over bar, was found to be high in the range 3-6. This result was attributed to strong attractive interactions between the growing radicals and the clay surface. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 4771-4784, 2011