Zinc coordination of carboxylate surfactomesogens to poly(4-vinylpyridine)

Zinc salts of carboxylic acid-functionalized alkoxybiphenyl mesogens (also termed surfactomesogens), HO2C(CH2) n-1PhPhOCH3, n = 6 and 11, Ph = phenyl, were melt-blended with poly(4-vinylpyridine), mainly at a mesogen/(vinylpyridine) molar ratio of 0.5, and studied by infrared spectroscopy, differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. Melt-blending results in complexation between the two components via zinc coordination (at the same maximal level for n) 6 and 11), and the complexes obtained are temporally stable at ambient temperature. The complex with n) 6 appears to be simply amorphous, with some excess surfactomesogen in crystalline form. In contrast, the complex with n) 11 is mesomorphic, structurally organized as a single-layer smectic A phase at ambient temperature, with no crystallization of excess surfactomesogen. It is concluded that a spacer length of 6 is not sufficient to decouple the biphenyl core from the coordination site so as to permit liquid crystal ordering, whereas this is possible for a spacer length of 11. At temperatures above 100 degrees C, decomplexation accompanied by crystallization of most of the surfactomesogen occurs in both systems (with complexation obtained again above the melting point). These complexes are the first examples in the literature, to our knowledge, of metal-coordinated comblike polymers involving surfactomesogens ( as opposed to simple surfactants) and show the interest of this metallosupramolecular approach for the conception of novel side-chain liquid crystal polymers.