Comparison of characteristics of SAN-MMT nanocomposites prepared by emulsion and solution polymerization

Nonextractable styrene-acrylonitrile copolymer-montmollironite (SAN-MMT) nanocomposites were prepared by two different intercalation process: (1) a usual one-step emulsion copolymerization in the presence of the Na+-MMT; and (2) a solution copolymerization with MMT modified by dimethyl dihydrogenated tallow ammonium. For comparative purposes, the copolymerization conditions (such as comonomer feed ratio and the polymerization temperature and times) were set up to be the same. The X-ray diffraction pattern demonstrated that the net increase of basal spacing of the purified emulsion products (0.76 nm) far exceeded that of composite (0.39 nm) prepared by solution method. The average molecular masses recovered from the composite extracts revealed M-w = 53 x 10(4) for emulsion products, while the composite made by solution yielded M-w = 4.8 x 10(4) g/mol. Likewise, the hybrid from the emulsion polymerization exhibited higher stress at maximum load over the solution products. The dispersibility of MMT particles in the polymer matrix was investigated by using optical microscopy (OM) and scanning electron microscopy (SEM) for those unextracted samples. It was found that almost complete hybrids were obtained when the styrene (ST)-acrylonitryl (AN) comonomer was emulsion polymerized in the presence of Na+-MMT, yielding both better miscibility and intercalation capability. (C) 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2811-2819, 1999.