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Nanocomposites based on polystyrene (PS) and organophilic layered silicates (organoclays) were prepared and characterised with respect to their morphological and rheological properties. The organoclays were obtained by means of ion exchange of clay with protonated, amine‐terminated PS. Two different exchange agents – a high (Mw = 5 800 g/mol) molecular mass amine functionalised PS, and 2‐phenylethylamine – were used to study the influence of their molecular weight on morphological and rheological properties of corresponding composites. Wide‐angle X‐ray scattering measurements show a significant increase in the interlayer spacing upon the ion exchange. Composites of organoclay prepared from the high molecular mass amine‐terminated PS and PS‐matrix polymer reveal a fine and stable dispersion of exfoliated silicate layers in the PS matrix if the compounding time in a conical twin screw extruder exceeds 180 s at a temperature of 200 °C. This composite, i.e. nanocomposite, shows unique elastic properties which can be understood quantitatively if one assumes that above a characteristic concentration of about 1 vol.‐% percolating strands of platelets are present in the material. Composites of PS and organoclay prepared from 2‐phenylethylamine did not exfoliate and consequently exhibited the rheological behaviour of a conventional composite. Qualitatively all morphological and rheological features of the PS nanocomposite can be entirely understood if one considers this material as a mixture of hairy platelets dispersed in an entangled PS matrix.

Poly(methyl methacrylate) (PMMA), polystyrene (PS), and polyurethane (PU) nanocomposites containing well‐dispersed calcium phosphate/layered silicate hybrid nanoparticles were prepared in a versatile solvent‐free “one‐pot” process without requiring separate steps, such as organophilic modification, purification, drying, dispersing, and compounding, typical for many conventional organoclay nanocomposites. In this “one‐pot” process, alkyl ammonium phosphates were added as swelling agents to a suspension of calcium/layered silicate in styrene, methyl methacrylate, or polyols prior to polymerization. Alkyl ammonium phosphates were prepared in situ by reacting phosphoric acid with an equivalent amount of alkyl amines such as stearyl amine (SA) or the corresponding ester‐ and methacrylate‐functionalized tertiary alkyl amines, obtained via Michael Addition of SA with methyl acrylate or ethylene 2‐methacryloxyethyl acrylate. Upon contact with the calcium bentonite suspension, the cation exchange of Ca2+ in the silicate interlayers for alkyl ammonium cations rendered the bentonite organophilic and enabled effective swelling in the monomer accompanied by intercalation and in situ precipitation of calcium phosphates. According to energy dispersive X‐ray analysis, the calcium phosphate precipitated exclusively onto the surfaces of the bentonite nanoplatelets, thus forming easy‐to‐disperse calcium phosphate/layered silicate hybrid nanoparticles. Incorporation of 5–15 wt% of such hybrid nanoparticles into PMMA, PS, and PU afforded improved stiffness/toughness balances of the polymer nanocomposites. Functionalized alkyl ammonium phosphate addition enabled polymer attachment to the nanoparticle surfaces. Transmission electron microscopy (TEM) analyses of PU and PU‐foam nanocomposites, prepared by dispersing hybrid nanoparticles in the polyols prior to isocyanate cure, revealed the formation of fully exfoliated hybrid nanoparticles.

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