Impact of the clay organic modifier on the morphology of polymer–clay nanocomposites prepared by in situ free-radical polymerization in emulsion

Graphical Abstract

Poly(styrene-co-butyl acrylate)–clay nanocomposites were synthesized by free radical polymerization in emulsion, using 10% of clay surface modified with various surface modifiers. The morphology of the nanocomposites obtained (i.e. intercalated, partially exfoliated, or fully exfoliated) was found to be strongly dependent on the chemical structure of the clay modifier, its degree of interaction with clay, and its ability to copolymerize with the monomers. Accordingly, due to the difference in their morphologies, the thermal stability and thermomechanical properties of the nanocomposites were found to be significantly dependent on the type of the clay modifier used. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Abstract

Poly(styrene-co-butyl acrylate) copolymers were prepared by free-radical random copolymerization of styrene and butyl acrylate in emulsion in the presence of 10% of surface-modified sodium montmorillonite (Na-MMT). The objective of this work was to evaluate the impact of the clay organic modifier in terms of its chemical structure, its degree of interaction within the clay galleries surface, and its ability to copolymerize with monomers, on the morphology and properties of the final nanocomposite prepared. Na-MMT was modified using different organic modifiers, namely: sodium 1-allyloxy-2-hydroxypropyl (Cops), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), N-isopropylacrylamide (NIPA), and sodium 11-methacryloyloxy-undecan-1-yl sulfate (MET), respectively. The morphology and properties of the nanocomposites obtained were found to be dependant on the clay organic modifier. X-ray diffraction (XRD) and transmission electron microscopy indicated that, nanocomposites at 10% clay loading with Cops-, NIPA-, and MET-modified clays, yielded intercalated to partially exfoliated structures, whereas AMPS-modified clay gave a nanocomposite with a fully exfoliated structure. All polymer–clay nanocomposites were found to be more thermally stable than neat poly(S-co-BA) as were determined by TGA. However, nanocomposites with intercalated structures exhibited greater thermal stability relative to fully exfoliated ones. Furthermore, nanocomposites with exfoliated structures exhibited higher storage moduli (G^I) than partially exfoliated once, whereas intercalated structure showed the lowest G^I values. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3619–3628, 2008