Revisit to the Formation Mechanism of Exfoliated Montmorillonite/PMMA Nanocomposite Latex Through Soap-Free Emulsion Polymerization

Soap-free emulsion polymerization of methyl methacrylate (MDAA) in the aqueous suspension of montmorillonite (MMT) was able to fabricate the exfoliated MMT/PMMA nanocomposite latex. Because neither MMA nor substantial quantity of potassium persulfide (KPS) initiator could be individually absorbed into the interlayer region of MMT, the polymerizing ionic radicals in water phase were considered as a major component to diffuse into the gallery of MMT. They have been observed to organize into disk-like micelles in the interlayer regions to exfoliate MMT. The diffusion of the polymerizing ionic radicals was further supported by using sodium dodecyl sulfate (SDS) surfactant as a model compound to diffuse into the gallery of MMT. The exfoliation of MMT was almost completed before micellization stage was over. After exfoliation, the disk-like micelles became a polymerization loci for monomers. Because the disk-like micelles in numbers were substantially over the commonly formed spherical micelles in the typical soap-free emulsion polymerization, the conversion rate of MMA to MMT/PMMA nanocomposite latex was faster. Based on the above experimental observation, a justified exfoliation mechanism of MMT was proposed. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 459-466, 2009