New hybrid nanocomposites based on an organophilic clay and poly(styrene- b -butadiene) copolymers
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New hybrid nanocomposites based on an organophilic clay and poly(styrene-b-butadiene) copolymers Michele Laus Dipartimento di Chimica Industriale e dei Materiali, Viale Risorgimento 4, I40136 Bologna, Italy
Oriano Francescangeli Dipartimento di Scienze dei Materiali e della Terra, Universit`a di Ancona, I60131 Ancona, Italy
Franco Sandrolini Dipartimento di Chimica Applicata e Scienza dei Materiali, Viale Risorgimento 2, I40136 Bologna, Italy (Received 14 June 1996; accepted 17 July 1997)
The preparation, by direct melt intercalation, and the properties of new hybrid organic-inorganic nanocomposites, consisting of a commercial sample of poly(styreneb-butadiene) copolymer (SBS) and a commercial organophilic clay containing the dioctadecyl dimethyl ammonium salt are described. In addition, several mixtures between the same copolymer and an unfunctionalized clay were prepared and studied. XRD spectra showed a partial insertion of the SBS block copolymer segments in the interlayers of the organophilic clay, accompanied by a loss of correlation within the layers. The degree of insertion increased by annealing the nanocomposites at 120 ±C for increasing time periods. No interaction between the polymer matrix and the unfunctionalized clay was found. The storage modulus value, in the plateau region between the glass transition processes of the polybutadiene and the polystyrene blocks, and the glass transition temperature of the polystyrene block domain increase as both the organophilic clay content and the annealing time increase. The glass transition process of the polybutadiene block domain is practically unaffected by the filler content and the annealing treatments. These data are most promising for upgrading the thermo-mechanical behavior and the application temperature window of the SBS thermoplastic elastomers through the preparation of nanocomposites employing suitably designed organophilic clays.
I. INTRODUCTION
Nanocomposites are a fascinating class of materials both in terms of fundamental interest and practical applications. On account of their peculiar volume and interface effects, these nanostructured materials can exhibit unusual and unexpected properties as compared to the same materials endowed with larger size structures.1 Accordingly, the control and design of the characteristic structural features on the nanometer scale allows materials to be obtained with tailored properties for a diversity of advanced structural,2 magnetic,3 catalytic,4 and biomedical applications.5 A special case of nanocomposites,6–11 called hybrid organic-inorganic nanocomposites, is represented by those prepared from polymeric materials and layered inorganic additives, like clay phillosilicates. By appropriately tuning the polymer-clay interactions, for example by suitably modifying the clay surface through the exchange of the interlayer cations with ammonium salts containing long alkylic chains, it is possible to obtain nanocomposites with a good dispersion degree. The expected pro
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