The thermal stability of alternating ethylene-carbon monoxide copolymers (POK-C-2), synthesised using a palladium-bidentate catalyst, is predominantly determined by the amount of 'active' catalyst species present in as-synthesised polymer for a palladium content >6 ppm. For a lower active palladium content the intrinsic limitations to the thermal stability of the chemical structure become noticeable. It is demonstrated that the thermal stability of polymers prepared under optimised conditions, (e.g. low catalyst content) is sufficient to allow melt processing for at least a few minutes of residence time above the melting temperature. Homogeneous transparent melt crystallised films are obtained and small strands were drawn at 225 degrees C to a ratio of 8. The mechanical properties of these oriented samples are comparable with commercially available PET and PA-6,6 melt spun fibres. The crystalline fraction in these samples is mainly present in the very dense POK-alpha form, indicating that the formation of a significant amount of bulky chain defects during thermal exposure, like Paal-Knorr and aldol type condensation products, is prevented.