Ordered assembly of conjugated ionic polyacetylenes within clay nanoplatelets: layer-by-layer assembly and intercalative polymerization

In this work, we prepared conjugated ionic polyacetylenes from 2-ethynylpyridine activated by strong acid and then assembled the ionic polymers with the exfoliated clay nanoplatelets through electrostatic layer-by-layer deposition technique. The structural ordering, conformation of the polymers within the clay layers, and thermal stability of the layer-by-layer assembled films were investigated and compared with the nanocomposite prepared by in-situ intercalative polymerization, in which 2-ethynylpyridine was intercalated and spontaneously polymerized within the clay layers. UV/Vis absorption spectroscopy measurement indicated that the sequential assembly between the clay nanosheets and polyacetylenes was linear with the deposition cycles and was also reproducible. Thermogravimetry analysis (TGA) showed that the loading density of the clay and polyacetylenes in the multilayer films was 3.79 × 103 g/(m2 bilayer) and 9.48 × 104 g/(m2 bilayer), respectively. Thickness of the clay and the polyacetylene layers in the multilayer films was estimated to be about 1.4 nm and 0.6 nm, respectively. X-ray diffraction (XRD) data showed that the multilayer films generated apparent Bragg peaks indicative of a structural order and single layers of polymer chains were deposited within the clay layers. Polarized absorption spectroscopy suggested that the polymer chains were oriented parallel to the plane of the multilayer films. Also the polymers in the layer-by-layer assembled films exhibited highly enhanced thermal oxidative stability. Such structural ordering, conformation of the polymers within the clay, and thermal oxidative stability of the layer-by-layer assembled films were comparable with the nanocomposite by in-situ intercalative polymerization.