| Abstract: | Poly(vinyl alcohol) single crystal platelets having a stepheight of approximately 100 A. were obtained by isothermal crystallization from dilute triethylene glycol solution. Material crystallized at temperature Tc redissolved in the same solvent at a higher temperature Ts. A plot of Tc versus Ts gave a straight line of slope 0.47. Extrapolation of this line to Tc = Ts gave (Tm)∞, which may be regarded as the dissolution temperature of the crystal of infinite stepheight. (Tm)∞ for this sample in triethylene glycol was 220°C. The crystalline nature of the platelets was established by electron and x-ray diffraction techniques. A total of three Bragg d spacings having the values of 3.9, 4.4, and 4.6 A. (±0.05 A.) were measured. These spacings were indexed as the (200), (101), and (101 ) reflections, respectively, of the monoclinic unit cell of Bunn. The x-ray diffractogram exhibits sharp intensities of the (101 ) and (101) reflections. The crystallinity calculated from the density of the poly(vinyl alcohol) precipitated from dilute solutions in triethylene glycol was 42%. Although the overall degree of crystalline perfection of this poly(vinyl alcohol) is low, the linear relationship between Ts and Tc and the formation of definite shaped single crystals when crystallized from dilute solution suggest that poly(vinyl alcohol) crystallizes in the same manner as other semicrystalline polymers. |
