Study on synthesis of polymer/silicate nanocomposites by emulsion polymerization and their characterizations

Abstract

Polymer/silicate nanocomposite, a new composite having the structure of individual clay layers uniformly dispersed in polymer matrix, exhibits excellent mechanical properties that are not expected from conventional composites. We synthesized several types of PMMA, PAN, SAN/silicate nanocomposites by emulsion polymerizations with pristine clay. The role of the reactive surfactant on the synthesis of exfoliated polymer/silicate nanocomposites were explained and the mechanical properties of the nanocomposites were characterized. With a reactive surfactant, AMPS, containing amido portion and sulfonic acid, the exfoliated PMMA/pristine Na-MMT nanocomposites were synthesized via a soap-free emulsion polymerization, and with the conventional anionic surfactant, DBS-Na, the intercalated nanocomposites were produced. The former composites showed the exfoliated morphology up to 10 wt % of Na-MMT and the exfoliation was confirmed by TEM. They were exfoliated within 10 minutes after polymerization was initiated. The dispersions of Na-MMT in water with MMA and surfactants showed no peak in X-ray diffraction pattern, which meant the enlargement of the basal spaces of silicate layers by the intercalation of surfactants. Even after the dispersions were freeze-dried, both surfactants remained in the silicate layers showing two types of intercalated states. With $T_g$A analysis of nanocomposites with AMPS, the residual molecules were end-tethered on silicate layers and showed more isotactic and less heterotactic configurations than the bulk PMMA. The glass transition temperature of the nanocomposite with AMPS became higher while that with DBS-Na decreased as the amount of Na-MMT increased. A0.3M20T10% showed the 44 % higher value of storage modulus than D2.5M20T10%. We extended this method to PAN, and describe a simple and convenient way to obtain exfoliated PAN/Na-MMT nanocomposites through in-situ polymerization with 2-acrylamido-2-methyl-1-propanesulfonic acid (A...