Crystal and molecular structure of poly(thioether-ketone) from single crystal oligomer data and diffraction-modelling: I. Polymer crystallised by orientation

The aromatic poly(thioether-ketone) [ArSArCO](n)(Ar = 1,4-phenylene) is kno wn to exist in two different crystalline forms, one produced by orientation of the amorphous polymer and the ether by heat treatment or crystallisatio n from the melt. In the present work, single crystal X-ray data for the oli gomer [ArCOArSArCOAr] rc:veal that bond angles at the thioether and carbony l linkages are substantially different, at 108 degrees and 121 degrees resp ectively, and that the linear chain-conformation required for polymer cryst allisation is achieved by a series of bond-angle distortions elsewhere in t he molecule-in particular by pyramidalisation of the carbon atoms adjacent to the thioether bridge. Crystal and molecular simulation of orientation-cr ystallised poly(thioether-ketone) shows that the unit cell is analogous to the "Form II" cell known for poly(etherketone)s. The polymer crystal struct ure thus has orthorhombic symmetry (two chains per cell), space group Pb2n, ct = 4.12, b = 11.30, c = 10.44 Angstrom, and density 1.45 g cm(-3). The p reviously reported monoclinic unit cell is shown to be based on a modificat ion of the present orthorhombic lattice. (C) 1999 Elsevier Science Ltd. All rights reserved.