A kinetic investigation of surfactant-free emulsion polymerization of styrene using Laponite clay platelets as stabilizers

Abstract : 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 a poly(ethylene glycol) monomethylether methacrylate (PEGMA) macromonomer. 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 (eventually containing adsorbed PEGMA molecules) leading to primary precursor particles composed of a single (or only a few) polymer chain 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. Therefore, the number of nucleated particles was not directly related to the number of Laponite platelets but was dependent on the PEGMA concentration. 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 , 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. Hence, radical absorption by the latex particles was greatly enhanced by the presence of the Laponite platelets on the particle surface and increased with increasing Laponite or PEGMA concentrations. Furthermore, it was found that the presence of monomer droplets destabilized the latex particles by adsorbing Laponite on its surface. The employment of a semicontinuous process enhanced particle stability by avoiding the presence of monomer droplets. Advantages of the semi-continuous process are also related to the elimination of the gel effect during which the reaction rate and temperature release may become uncontrollable, and consequently the polymer molecular weight may increase importantly.
Type de document :
Article dans une revue
Journal of Polymer Science Part A: Polymer Chemistry, Wiley, 2011, 49 (22), pp.4771-4784. 〈10.1002/pola.24924〉
Domaine :
Liste complète des métadonnées

https://hal.archives-ouvertes.fr/hal-00925097
Contributeur : Nida Sheibat-Othman <>
Soumis le : mardi 7 janvier 2014 - 15:20:15
Dernière modification le : jeudi 19 avril 2018 - 14:46:15

Lien texte intégral

Identifiants

Collections

Citation

Nida Sheibat-Othman, Elodie Bourgeat-Lami, Elodie Bourgeat-Lami, Amilton Martin Dos Santos, Ana-Maria Cenacchi-Pereira. A kinetic investigation of surfactant-free emulsion polymerization of styrene using Laponite clay platelets as stabilizers. Journal of Polymer Science Part A: Polymer Chemistry, Wiley, 2011, 49 (22), pp.4771-4784. 〈10.1002/pola.24924〉. 〈hal-00925097〉

Partager

Métriques

Consultations de la notice

156