Nanocomposites from in-Situ Polymerization of Substituted Polyacetylene within Lamellar Surface of the Montmorillonite:  A Solid-State NMR Study

Nanocomposites prepared by in-situ polymerization of 2-ethynylpyridine (2EPy) in the presence of a layered aluminosilicate such as Ca2+−montmorillonite (MMT) were characterized by solid-state 13C cross-polarization/magic angle spinning (CP/MAS) NMR spectroscopy. The structure and dynamics of the polymer layer inserted between the montmorillonite lamellae were investigated. The 13C NMR chemical shifts of the polymer component of the nanocomposite that was prepared by in-situ polymerization were assigned by analyzing the difference between the chemical shift values of the bulk and bulk-intercalated poly(2-ethynylpyridine) (P2EPy) nanocomposite material. The results of solid-state NMR and X-ray diffraction studies clearly demonstrate a spontaneous polymerization of 2EPy within the galleries of MMT. The polymer thus formed is mostly bound to the surface of MMT at either the Brønsted or Lewis acid sites. Infrared analysis suggests the existence of positive charge on the nitrogen atom of the polymer inside the lamellar gallery. Bulk synthesized P2EPybulk in both protonated and deprotonated formwas also intercalated and studied by solid-state NMR. The variation in charge distribution of P2EPy intercalated under different conditions is also discussed.