Differential scanning calorimetry and high temperature x‐ray diffraction were used to study the perfectly alternating copolymer of ethene and carbon monoxide (polyketone; POKC2). It was found that oriented POK‐C2 fibers show a crystalline phase transition at a temperature between 110–125°C with a 10% change in crystalline density. At this temperature, the crystal structure reported recently (POK‐α) is transformed to a crystal structure that was reported in the past for room temperature imperfectly alternating polyketone. The latter structure will be designated as POK‐β. The influence of chain defects on the crystal structure was studied by synthesizing terpolymers (POK‐C2/C3), in which small amounts of propylene‐CO units are incorporated into the polymer backbone. The resulting terpolymers differ from the copolymer by the presence of methyl groups randomly distributed along the polyketone backbone chain. Evidence is presented that indicates that the methyl groups are built into the crystal lattice as defects. With more than 5 mole‐% propene the terpolymer fibers crystallize exclusively in the β‐modification. Below this level the α/β ratio (at room temperature) increases with decreasing amounts of propene. Both as‐synthesized and as‐spun POK‐C2 were found to consist of both POK‐α and POK‐β; the α/β ratio depends on the method of preparation. Because the drawn POK‐C2 fibers studied here consist exclusively of POK‐α, the process of spinning and drawing leads to the transformation of unoriented β‐rich material into oriented POK‐α. © 1995 John Wiley & Sons, Inc.

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) Aå, b = 5.12 (2) Aå, c = 7.60 (3) Aå (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.

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