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Two series of new, wholly aromatic copolyesters were prepared from 6-hydroxy-5-phenyl-2-naphthoic acid (HPNA) or 4‘-hydroxy-3‘-phenyl-biphenyl-4-carboxylic acid (HPBA) and 4-hydroxybenzoic acid (HB...

Force fields with good transferrability for poly(p-hydroxybenzoic acid) and for poly(6-hydroxy-2-naphthoic acid) were developed on the basis of a fit of the force field parameters to the results from semiempirical AM1 calculations. The dihedral terms in the force field describing the rotations in the ester linkages are the most important ingredients with respect to modeling of the conformational properties of these macromolecules. These torsional barriers were scaled by a factor of 1.9 as proposed in the second paper of this series. Very good agreement between the scaled AM1 potential energy surface and the fitted force field was obtained

A new polymorphic structure is found in the annealed fibers of the 75/25 HBA/HNA copolymer, which coexists with the structure first reported for the as-spun state. These two structures show striking similarities to those for homopoly(HBA), and a model for the 75/25 copolymer based on analogy to the homopolymer structure is refined using the linked atom least-squares method to obtain the best agreement between the observed and calculated X-ray intensities

Three samples of poly(6-oxy-2-naphthoate) were prepared under different reaction conditions, whiskers were obtained in one case. The properties of all three samples are studied. A reversible phase transition from an orthorhombic to a nearly pseudohexagonal chain packing occurs at 330-350 °C, and a second reversible transition associated with the change of rotational freedom of naphthalene rings occurs at 440-460 °C. Both phase transitions depend significantly on the reaction conditions used for the preparation of the sample. The whiskers proved to be the chemically and physically most perfect form of all three poly(6-hydroxy-2-naphthoic acid) samples

The PHBA homopolymer displays a shallow relaxation at low temperature and a stepwise increase in dielectric constant for all frequencies at the high-temperature crystal-to-smectic E transition, while the copolyesters display two solid-phase relaxations with increasing temperature that appear to correlate with localized rotations of the HBA units and combined rotations and translations of chain segments, respectively. These results are consistent with previously reported dielectric and dynamic mechanical data