Abstract
A series of films were prepared from anisotropic poly(p-phenyleneterephthalamide) (PPT) solutions and annealed at 100, 200, and 300 °C. By using cross polarized light microscopy, the PPT films appeared to exhibit a completely anisotropic morphology. From X-ray diffraction analysis, each of the films appeared to contain a fixed level of modification II crystallites with the level of modification I crystallites increasing with annealing temperature. Amorphous films were also prepared from a structural isomer of PPT which contains a large fraction of meta linkages along the polymer main chain. Permeability measurements were made for He, H2,02, N2, and CO2 at 35 °C and the diffusivities of the larger gases were computed from time-lag data. In general, the permeability coefficients of the PPT films are very low and approach those reported for poly(acrylonitrile) (PAN) and liquid crystalline copolyesters. The oxygen permeability coefficients of the amorphous PPT isomer are over 1 order of magnitude larger than those for the anisotropic PPT materials. The solubility coefficients for the noncrystalline regions of the PPT and PPT isomer, however, are very close. In contrast with the well-documented effect of meta- versus para-linked moieties on transport in amorphous, glassy polymers, the mesomorphic para-linked PPT materials exhibit oxygen diffusion coefficients that are nearly 1 order of magnitude lower those of the meta-linked PPT isomer. Among the PPT films, the permeability coefficients of the samples annealed at 100 and 200 °C are nearly the same, while annealing at 300 °C results in significant reductions in both permeability and diffusivity.