Crystal structure of polyketone (1:1 ethylene/carbon monoxide copolymer)

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Abstract
The crystal structure of polyketone (1:1 ethylene/carbon monoxide copolymer) obtained by γ‐irradiation copolymerization of ethylene and carbon monoxide was determined by x‐ray diffraction. An orthorhombic unit cell was found, having space group D (Pnam) of dimensions a = 7.97, b = 4.76, c (fiber axis) = 7.57 A. The unit cell contains four repeating units (CH2CH2CHO). The main chain has a planar zigzag form. The side‐by‐side molecular packing is analogous to that of polyethylene, and CO groups arrange at two equivalent levels, z = 1/4 and 3/4. An apparent anisotropic thermal vibration of the molecule was recognized; i.e., the thermal vibration in the direction perpendicular to the fiber axis is about three times that along the fiber axis. Furthermore, from a preliminary investigation on polyketones having several mole ratios of ethylene and carbon monoxide, an interesting result was found: the larger the fraction of CO, the longer the a axis and the shorter the b axis.