Molecular and crystal structure of poly(vinylidene chloride)

The molecular and crystal structure of poly(vinylidene chloride) were determined by X-ray structure analysis together with conformational energy calculation. The crystals are monoclinic P21 or P21/m with cell dimensions a = 6.71 A, b (fiber axis) = 4.68 A, c = 12.51 A, and β = 123deg, and there are four monomeric units (two chains) in the unit cell. The molecular conformation is a glide (TGTG) form: the internal rotation angles of two successive backbone bonds are 175deg (T) and 49deg (G'), and the C-CH2-C and C-CCl2-C bond angles are 123deg and 114deg, respectively. The deviation of the internal rotation angle from 60deg (G) to 49deg (G') and the large C-CH2-C bond angle are ascribable to the steric hindrance between the chlorine atoms of adjacent monomeric units. From the X-ray study, the great possibility of a disorder with respect to the packing of upward and downward chains in the crystal lattice (space group P21/m) is inferred. (author)