To resolve long-standing uncertainties surrounding the bridge-bond angles of crystalline poly(aryletherketone) s, the structure of an oligomeric ether-ketone, CIArCOArOArCOArC1 (Ar = 1,4-phenylene), has been determined by single crystal X-ray methods. The average torsion angle ~b of the two 'ether-ketone' rings, relative to a plane defined by the bridging oxygen and carbonyl-carbon atoms is 31 °. The bond angles at carbonyl-carbon and ether-oxygen are 121.9 (3) ° and 121.2 (3) °, respectively, values which are substantially lower than those consistently reported for poly(aryletherketone)s on the basis of X-ray powder- and fibre-diffraction studies. [An average bridge-bond angle of 126.5 (6) ° has, for example, been proposed to account for the c-axis length of 10.09(2) in the prototype poly(etherketone) (PEK) (-OArCOAr-),.] Despite this apparent difference in bridge-bond angles, a PEK c-axis distance of 10.11 (1)A, entirely consistent with that of the polymer, is found in the present oligomer structure. More detailed analysis of the oligomer structure reveals a pattern of sterically induced bond angle distortions at the aromatic carbon atom linked to an ether or ketone bridge, a pattern that is repeated in the X-ray structure of a second oligomer ArOArCOArArCOArOAr (Ar = phenyl or 1,4-phenylene). These findings strongly suggest that bridge-bond angles in poly (aryletherketone)s actually lie in the region of 121-122 °, and that the range 125-127 ° consistently reported in the literature is an artifact deriving from the assumption of ideal geometry elsewhere in the polymer chain.
Посилання на статтю:
Single crystal X-ray diffraction studies of aromatic oligomers' resolution of the bond-angle anomaly in poly ( a rylet herketone ) s / Howard M. Colquhoun* and Caroline A. O'Mahoney and David J. Williams // Polymer. – 1993. – Vol 34. – P. 218-221.