Clay-polyvinylpyridine nanocomposites

Nanocomposites of montmorillonite mineral with poly-4-vinylpyridinium salts (1,2-form) the quaternized ionene polymer (1,6-form) and poly-4-vinylpyridine (neutral form) have been synthesized and characterized. Only one macromolecular sheet of poly-4-vinylpyridinium polyelectrolyte or the quaternized polyelectrolyte enters the interlayer space, irrespective of the amount of the polyelectrolyte used in the intercalation. Exfoliated hybrids are not therefore generated with polycationic polymers. In contrast, partially protonated poly-4-vinylpyridine is adsorbed at variety of levels and may induce clay exfoliation. Polymerization of monomeric 4-vinylpyridinium salts in the clay galleries is faster than that of the pure 4-vinylpyridinium salt and results in the formation of the quaternized ionene form independently of the polymerization conditions. Adsorption isotherms for the different forms of poly-4-vinylpyridine reveal that surface saturation coverage increases in the following order: partially protonated poly-4-vinylpyridine > quaternized ionene form > completely protonated poly-4-vinylpyridine. Models explaining the different uptake of the three derivatives and the surface selectivity toward quaternized polycations are proposed. The electrochemical results confirm that intercalative polymerization produces only the quaternized form of the polymer and reveal that protonation of poly-4-vinylpyridine occurs because of the acidity of the clay layers.