NEUTRON STRUCTURE ANALYSIS OF POLY(VINYL ALCOHOL). Yasuhiro Takahashi, Department of Macromolecular Science, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan.

Two crystal structure models were proposed by Bunn and Sakurada et al., which were different in the azimuthal angle of the molecular plane and the hydrogen bonding network. In neutron diffraction, hydrogen atom contributes to the intensity more than X-ray diffraction. Therefore, it is possible to determine the azimuthal angle more accurately and to clarify the position of the hydrogen atom associated with the hydrogen bond. Commercially supplied poly(vinyl alcohol) fiber was used for the sample.

Neutron diffraction experiments were made at JAERI. The intensity distributions on the equator were measured at 100K, 200K, and room temperature. The integrated intensity was estimated after the indices were assigned. The refinements were carried out under the rigid-body assumption. Here, the hydrogen atoms associated with the hydrogen bonds were not incorporated, since the hydrogen atom positions cannot be assumed because of the statistical distribution of the oxygen atoms due to the atactic configuration. The refinements by using the data at 100K, 200K, and room temperature gave R-factors, 26.8, 24.8 and 20.3 %, respectively. The structures obtained are essentially the same as Bunn's model. The molecule slightly rotates as the temperature increases. The discrepancy factors are not so good. This may be attributed to the fact that the hydrogen atoms associated with hydrogen bonds were ignored. Therefore, the difference synthesis was made by using the data at 100K. It is possible to find three peaks on the map of the difference synthesis. Two peakes can be interpreted by the intermolecular hydrogen bonds as Bunn suggested. Third peak should be attributed to the intramolecular hydrogen bonds in the isotactic sequence of the atactic configuration, which was first proposed by Murahashi et al. for the isotactic poly(vinyl alcohol).