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Soap‐free emulsion polymerization of methyl methacrylate (MMA) 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. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 459–466, 2009

The exfoliated montmorillonite (MMT) nanoplatelets tended to re‐stack with each other after casting the MMT/poly(methylacrylate‐co‐methylmethacrylate) P(MA‐co‐MMA) latex solutions fabricated by soap‐free emulsion polymerization into films as revealed by X‐ray diffraction and transmission electron microscopy. As the content of MMT was increased from 0 to 20 wt %, the Tg measured by differential scanning calorimetry was slightly decreased from 19.2 to 17.2 °C, whereas that measured by dynamic mechanical analysis was increased from 22 to 32 °C, indicating that the local motion of polymer segments has been retarded by MMT nanoplatelets. Besides, the elongated elliptical voids appeared during stretching of 1 wt % MMT/P(MA‐co‐MMA) film to cracking also illustrated the pinning effect provided by the exfoliated MMT. As the content of MMT was increased more than 10 wt %, the mechanical behavior of MMT/P(MA‐co‐MMA) nanocomposite films was changed from ductile to brittle nature with significant increase of Young's modulus and tensile strength owing to the restacking of exfoliated MMT nanoplatelets. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1064–1069, 2010

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