CRYSTALLINITY IN POLY(VINYL ALCOHOL) - 1 - AN X-RAY-DIFFRACTION STUDYOF ATACTIC PVOH

The significant level of crystallinity in atactic poly(vinyl alcohol) results from the comparatively modest size of the OH group enabling it to assume d and I positions in an atactic chain within a single cryst al lattice. The structure is highly hydrogen bonded. An X-ray diffract ion investigation has been made of the crystal structure to determine the distribution of hydrogen bonds, to understand the crystalline ther mal expansion and to determine the influence of water on the polymer c rystals and crystallisation process. Thermal annealing treatments have been developed to obtain samples of the maximum level of crystallinit y with minimum disorder. The well-resolved diffraction peaks from such samples are analysed to measure the thermal expansion coefficients of the crystal unit cell which are related to the hydrogen bonding netwo rk in the crystal structure. Finally, the effect on the crystals of ab sorbing water into polymer of various levels of crystallinity and also during the crystallisation process is investigated, leading to the hy pothesis that water molecules may be incorporated within the random cr ystal structure resulting in a change in the relative intensities of t he diffraction peaks. (C) 1998 Elsevier Science Ltd. All rights reserv ed.