Crystal and molecular structure of poly(thioether-ketone) from single-crystal oligomer data and diffraction modeling. 2. Polymer crystallized from the melt or from solution

The aromatic poly(thioether-ketone) [ArSArCO](n) (Ar = 1,4-phenylene), PTEK , is known to exist in at least two different crystalline forms, one produc ed by orientation of the amorphous polymer and the other by crystallization from the melt. In the present work, X-ray powder diffraction studies inter faced to molecular modeling and diffraction simulation techniques have been used to determine the crystal and molecular structure of melt- or solution -crystallize PTEK. In this phase, the thioether-ketone polymer chains adopt a packing arrangement very different from that of their ether-ketone analo gues. For solution-crystallized polymer, the unit cell is body-centered mon oclinic (two chains per cell), space group I2, a = 7.58, b = 6.09, c = 10.2 5 Angstrom, beta = 93.7 degrees, density = 1.49 g cm(-3). The thermal param eters required for this model are however rather high, suggesting the possi bility of a disordered structure tin space group I2/a,) whereby thioether a nd ketone linkages are distributed at random over the available sites. Melt crystallization results in a very slight expansion of the crystal lattice in the a-direction, relative to the solution-crystallize form, but the stru cture is otherwise unchanged.