Highly isotactic poly(vinyl alcohol) derived from tert-butyl vinyl ether V.: Viscoelastic nehavior of highly isotactic poly(vinyl alcohol) films

Dynamic viscoeasticity of poly(vinyl alcohol) with high isotacticity (HI-PVA, mm = 0.78), being derived from tert-butyl vinyl ether, was investigated to compare with that of syndiotactc PVA (S-PVA, nun = 0.14) and commercial atactic PVA (A-PVA, mm = 0.22). In the non-crystalline region, the beta(a) (local twisting motion) and alpha(a) (micro-Brownian motion) dispersions occurring at around -10 degrees C and 70 degrees C were nearly the same, in both magnitude and location, for the HI-PVA and S-PVA having an almost identical degree of crystallinity. On the other hand, in the crystalline region, the beta(c) and alpha(c) dispersions of HI-PVA were somewhat different from those of ordinary PVAs. The beta(c) dispersion (local motion in crystals due to defects) was clearly observed for HI-PVA but not for S-PVA and A-PVA. The alpha(c) dispersion (axial motion of the chain in the crystal lattices) was observed for all PVA films but its temperature increased in the order of HI-PVA > S-PVA > A-PVA, which well corresponded to the order of the melting temperature and C-13 spin-lattice relaxation time (T-1C) of each stereoregular PVA. These differences may be attributed to a difference of the magnitude of intermolecular and/or intramolecular hydrogen bonding in the crystals of respective PVAs. Specifically, the successive intramolecular bonding in the HI-PVA crystal appears to reduce the magnitude of the intermolecular bonding thereby allowing the chain to exhibit the beta(c) motion. This successive bonding would also stiffen the chain backbone thereby increasing the alpha(c) dispersion temperature.