X-ray Analysis and Molecular Modeling of Poly(vinyl alcohol)s with Different Stereoregularities

摘要: Wide-angle X-ray methods have been used to compare the structures of poly(vinyl alcohol) (PVA) with syndiotactic diad (S-diad) contents in range 51−63%. The fiber diagram a PVA 51.2% S-diad content (essentially atactic) is indexed by monoclinic unit cell dimensions = 7.82 ± 0.03 A, b 2.53 0.01 A (chain axis), c 5.52 and β 91.5 0.2°. These are very similar those proposed Bunn (Nature 1948, 161, 929) Sakurada (Bull. Inst. Chem. Res., Kyoto Univ. 1950, 23, 78). As increased, crystallites become larger less distorted there lateral contraction crystal structure, suggesting that chains can pack more efficiently. For syndiotacticity-rich 63.1%, as follows:  7.63 0.02 2.54 5.41 91.2 0.1°. latter structure has theoretical density 1.40 g/mL, which ∼5% higher than value 1.34 g/mL pred...