Axially Oriented Nanoporous Crystalline Phases of Poly(2,6-dimethyl-1,4-phenylene)oxide

The aim of this paper is the achievement of films characterized by axially oriented nanoporous-crystalline (NC) and co-crystalline (CC) phases of poly(2,6-dimethyl-1,4-phenylene)oxide (PPO). Axially oriented films are generally suitable to determine host-guest relative orientations (by polarized IR spectra) and can facilitate the resolution of crystalline structures (by WAXD fiber patterns). This goal was achieved for the NC alpha form by using miscible blends of PPO with atactic polystyrene that exhibit reduced T-g and hence allow lower stretching temperatures (185-195 degrees C), thus avoiding formation of the dense mesomorphic gamma form. Lower stretching temperatures also avoid loss of crystallinity (as proved by nearly unaltered melting enthalpies) and avoid polymer oxidation (as shown by the absence of the IR oxidation band at 1696 cm(-1)). Polarized IR spectra of axially oriented alpha and ss form films allow establishment of directions of transition moment vectors of PPO vibrational bands, which are in agreement with those previously hypothesized on the basis of band relative intensities for films presenting different planar orientations. The sign of the IR linear dichroism of the 677 cm(-1) benzene guest band allows establishing that benzene guest molecules are oriented with their molecular plane roughly parallel to the PPO crystalline chain axes.