STRUCTURES OF POLY(2-HYDROXY-6-NAPHTHOIC ACID) AT AMBIENT AND HIGH-TEMPERATURES

The structures of poly(2-hydroxy-6-naphthoic acid) (PHNA), (C10H6COO)x, at room and high temperatures accompanying the phase transition at ca. 340 have been determined by X-ray powder diffraction analysis. The PHNA data at room temperature can be explained by an orthorhombic cell with a = 7.66 (1) angstrom, b = 5.98 (1) angstrom, and c = 17.12 (3) angstrom, space group Pbc2(1) (four C10H6COO units, rho(calc) = 1.44 g cm-3), and the naphthoic rings staggered by ca. 120-degrees along the chain. Disorder has been considered in the packing by giving equal occupancy to the two molecules oriented up or down along the c cell axis and some degree of molecular mobility along the c axis. The space group Iba2 was found at 370-degrees-C with the cell parameters a = 9.28 angstrom, b = 5.64 angstrom, and c = 17.04 angstrom (four C10H6COO, rho(calc) = 1.27 g cm-3). The new structure can be explained starting from the room temperature one by applying a rotational statistical model involving a 2-fold axis around the chain axis, analogous to a smectic E phase.