Scientific Publications of Jos Aerts

Abstract

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-alfa) is as follows: Space group Pbnm, a=6.91(2)A, b=5.12(2)A, c=7.60(3)A (fiber axis), rho(c)=1383 kg/m3. This differs from the structure reported earlier by Chatani et al. (POK-beta). The very dense packing in the POK-alfa 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 of 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.