STRUCTURE AND MELTING OF PERFECTLY ALTERNATING ETHYLENE CARBON-MONOXIDE COPOLYMERS

The perfectly alternating ethylene carbon monoxide copolymer (polyketo ne; POK) has been studied by means of H-1 nuclear magnetic resonance a nd thermal analysis, and the crystal structure, determined by wide ang le x-ray scattering methods, is presented. The crystal structure of th is polymer in well-oriented fibers (POK-alpha) is as follows: Space gr oup Pbnm, a = 6.91 (2) angstrom, b = 5.12 (2) angstrom, c = 7.60 (3) a ngstrom (fiber axis), rho(c) = 1383 kg/m3. This differs from the struc ture reported earlier by Chatani et al. (POK-beta). The very dense pac king in the POK-alpha structure is a result of the arrangement of the dipoles in the crystal lattice, giving rise to strong lateral forces b etween 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 derive d 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 h igh-modulus polyethylene fibers. (C) 1993 John Wiley & Sons, Inc.