 An even higher service temperature can be reached by linking of aromatics (e.g.phenyl) with oxygen (as diphenyl ether group e. g. PEEK), sulfur (as diphenyl sulfone groups in PES or diphenyl group, for example in PPS) or nitrogen (imide group in PEI or PAI.Resulting operating temperatures might be between 200 °C in the case of PES to 260 °C in case of PEI or PAI.