Structure and melting of perfectly alternating ethylene‐carbon monoxide copolymers

The perfectly alternating ethylene carbon monoxide copolymer (polyketone; POK) has been studied by means of 1H nuclear magnetic resonance and thermal analysis, and the crystal structure, determined by wide angle x-ray scattering methods, is presented. The crystal structure of this polymer in well-oriented fibers (POK-α) is as follows: Space group Pbnm, α = 6.91 (2) Aa, b = 5.12 (2) Aa, c = 7.60 (3) Aa (fiber axis), pc = 1383 kg/m3. This differs from the structure reported earlier by Chatani et al. (POK-β). The very dense packing in the POK-α structure is a result of the arrangement of the dipoles in the crystal lattice, giving rise to strong lateral forces between the polymer chains. Owing to the all-trans conformation of the polymer chain in the crystal lattice, high moduli can be achieved for well-oriented fibers. A first approximation results in a value of 360 GPa for the theoretical modulus. From the melting data for a series of low molecular weight polyketone homologs, a first, estimate is derived for the crystalline heat of fusion (215–330 J/g) for infinite chain length. As a result of the strong lateral forces, this polymer shows a (very) high crystalline heat of fusion, whereas creep and compressive strength of oriented fibers are expected to be superior to those of high-modulus polyethylene fibers. © 1993 John Wiley & Sons, Inc.