Polyether Ketones are polymers whose molecular backbone contain alternating ketone (R-CO-R) and Ether (R-O-R) functionalities. The most common are Polyaryletherketone (PAEK), in which there is an aryl group linked in the (1-4) position between each of the functional groups. The backbone, which is thus very rigid, gives the materials very high glass transition and melting temperatures compared to other plastics. Other types of polyetherketone are: PEKK – Polyetherketoneketone PEEKK – Polyether ether ketone PEKEKK – Polyetherketoneetherketoneketone