Crystal and molecular structure of the thioether-analogue of PEEK from X-ray powder data and diffraction-modelling

Analysis of X-ray powder data for the melt-crystallisable aromatic poly(thioether thioether ketone) [-S-Ar-S-Ar-CO-Ar]_n, ('PTTK', Ar=1,4-phenylene), reveals that it adopts a crystal structure very different from that established for its ether-analogue PEEK. Molecular modelling and diffraction-simulation studies of PTTK show that the structure of this polymer is analogous to that of melt-crystallised poly(thioetherketone) [-S-Ar-CO-Ar]_n in which the carbonyl linkages in symmetry-related chains are aligned anti-parallel to one another, and that these bridging units are crystallographically interchangeable. The final model for the crystal structure of PTTK is thus disordered, in the monoclinic space group I2/a (two chains per unit cell), with cell dimensions a=7.83, b=6.06, c=10.35 Å, β=93.47°.