| Popis: |
The crystal lattice constants have been measured for PEEK and the related aromatic polymers PEEKEK, PEK, PEEKK, PEKEKK and PEKK. Measurements were made on uniaxially oriented film samples using the 110, 200 and 020 reflections from X-ray equatorial scans to determine the a and b parameters and using the 006 and 008 from meridional scans to determine c. All polymers are able to crystallize with a PEEK type cell, although the b and c parameters increase with the proportion of ketone links. At higher ketone content a new crystal form is able to occur alongside the normal PEEK cell. The new cell was the dominant form in the PEKK sample. The new cell in PEKK is orthorhombic with parameters a = 4.17 ± 0.02 A , b = 11.34 ± 0.04 A , c = 10.08 ± 0.01 A and density 1.395 ± 0.008 g ml−1. It is proposed that the new cell has the same symmetry, chain conformation and relative chain packing as the normal PEEK cell, but with a reduced and b enlarged. |
