EFFECT OF HYDROGEN-BONDING ON THE ANISOTROPY OF THE HYDROSTATIC COMPRESSIBILITY OF POLYMER CRYSTALS

In the reported experiments, correlations between the crystals structures of polymers consisting of the hydrogen-bonded molecular sheets and anisotropy of the linear compressibility (k//0) of the crystal were studied at 20 degree C under hydrostatic pressures up to 6 kbar. For nylon-6, it was found that k//0 is more than four times larger in the direction normal to the hydrogen-bonded sheet than in the parallel direction. The inversion of the sheet direction involved in the alpha yields gamma transition of nylon-6 was clearly reflected in the anisotropy of the linear compressibility. For atactic poly(vinyl alcohol), k**0 in the c-axis direction was 1. 6 times larger than that in the a-axis direction, which is consistent with a structure model with the hydrogen-bonded sheet parallel to the a axis. Theoretical calculations by Tashiro et al. indicate, however, the anisotropy does not necessarily correspond to the sheet structure when the direction of the hydrogen bonds strongly deviated from the plane of the sheet.