pubs.acs.org/Macromolecules Published on Web 12/08/2009 r 2009 American Chemical Society 448 Macromolecules 2010, 43, 448–453 DOI: 10.1021/ma901952p Interfacial Interactions in PP/MMT/SEBS Nanocomposites Zulima Martı´n,* ,† Ignacio Jim enez, ‡ M.  Angeles G omez, † Harald Ade, § and David A. Kilcoyne ^ † Instituto de Ciencia y Tecnologı´a de Polı´meros, ICTP-CSIC. Juan de la Cierva 3, 28006 Madrid, Spain, ‡ Instituto de Ciencia de Materiales de Madrid, ICMM.-CSIC. Campus de Cantoblanco, 28049 Madrid, Spain, § Department of Physics, North Carolina State University, Raleigh, North Carolina 27695, and ^ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720 Received September 2, 2009; Revised Manuscript Received November 18, 2009 ABSTRACT: The intercalation capability of poly(styrene-b-ethylene butylene-b-styrene) (SEBS) in nano- composites of isotactic polypropylene (PP) with 5 wt % of organically modified montmorillonite (C20A), prepared by melt blending, has been investigated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies have shown the presence of intercalated structures in the nanocomposite. In a previous research, we studied the intercalation capability of a commercial compatibilizer. 1 Those results, with the study we present in this work, allow us a better understanding of the mechanism of compatibilization and a deeper characterization of the structure and morphology of the nanocomposite. Scanning transmission X-ray microscopy (STXM) has been used. Because of the excellent chemical sensitivity and the high spatial resolution (∼40 nm) of this technique, we have proved that C20A is not in direct contact with the PP phase because the clay is always located inside the elastomer domains. The elastomer is surrounding the nanoclay, hindering the clay exfoliation and preventing its dispersion in the PP matrix. On the other hand, we have observed that the presence of the clay caused the SEBS particles to become elongated in shape and retarded the coalescence of the elastomer particles. Introduction Phenomena and processes at the nanometric scale have opened revolutionary possibilities in the development of new nanostruc- tured materials. In polymer systems, the addition of layered silicates leads to a great improvement in the properties of the matrix such as thermal stability and mechanical performance with very low filler contents. This is because the high surface area of these particles with nanometric dimensions increases the interfacial interactions between matrix and clay. 2-5 Therefore, the key factor for the enhancement in performance of the polymer/clay nanocomposites is the dispersion of the filler in the matrix since the final properties depend on the structure and morphology generated during the processing. Consequently, a significant research effort is dedicated to characterize the nano- structure in polymer nanocomposites. In this study, we have prepared isotactic polypropylene/ montmorillonite/poly(styrene- b-ethylene butylene- b-styrene) elastomer composites from the melt considering that this processing method is the most attractive for industrial application. 6-10 The addition of SEBS as a third component in the composite is intended to provide a better dispersion and intercalation of the silicate and also to provide a toughness improvement. Montmorillonite is the most commonly used layered silicate for the preparation of nano- composites because of its high aspect ratio, large surface area, and surface reactivity. Its structure consists on the stacking of aluminosilicate layers ∼1 nm thick, with a regular spacing between them of ∼1.5 nm. Its high cation exchange capacity offers a way of modifying the interlayer spacing to make it larger and more compatible with polymers. However, unlike polymers with polar groups like polyamides, 3,6,11-13 in nonpolar polymers like poly- propylene (PP) the organic modification of the clay is not enough to achieve a good level of dispersion and hardly leads to mixed structures. 14-19 Therefore, compatibilizers like polypropylene- graft -maleic anhydride (PP- g-MA) are commonly used to improve interactions between the organic polymer and the inorganic filler. 20-23 In this work, we have studied the intercalation capability of a styrene-ethylene butylene-styrene triblock copolymer, SEBS, as an alternative to the use of common compatibilizers, such as the PP-g-MA mentioned above, in PP/montmorillonite nano- composites. In PP nanocomposites, an elastomer phase is nor- mally used to compensate for the reduction of toughness caused by adding inorganic fillers. 24,25 In principle, SEBS can aid the polypropylene chains to get into the nanoclay layers. Therefore, it can be expected that SEBS favors the intercalation and/or exfoliation. On the other hand, it has been reported that in these kinds of blends of immiscible polymers, e.g., PS/PP 26 or PBT/ PE, 27 the nanoclay acts modifying the interphase properties and so improving the compatibility between the different polymeric phases. SEBS presents a phase-separated morphology, and con- sequently, its interactions with the montmorillonite and its intercalation capability will be very different from the ones of common compatibilizers. The aim of this work is to investigate the structure, morphology, and interfaces of isotactic polypro- pylene-clay-elastomer nanocomposites prepared by melt mixing. X-ray diffraction (XRD) and transmission electron microscopy (TEM) are used to characterize the intercalation capability of the polymers. TEM microscopy alone cannot provide conclusive information about the compatibilization role of SEBS in the PP-clay system, since although the lack of chemical contrast between the SEBS and PP polymeric phases could be overcome by OsO 4 staining, the different TEM magni- fications needed to observe the rubber phase (in the range of micrometers) and the clays (in the range of nanometers) would make difficult to observe the three components simultaneously. Besides, no compositional chemical information is provided by this technique. *Corresponding author. E-mail: amiluz@hotmail.com.