The crystalline structure of a number of perfectly 1:1 alternating alpha-olefin:carbon monoxide aliphatic polyketones produced by the polymerisation of ethene with carbon monoxide (ECO polymers) and mixtures of ethene and propene with carbon monoxide (EPCO polymers) have been studied by wide angle X-ray scattering (WAXS), Raman spectroscopy and differential scanning calorimetry (DSC). It is further confirmed that both WAXS and Raman spectroscopy are suitable techniques for the characterisation of the two polymorphs (alpha and beta) reported for these materials. DSC detected the presence of small endotherms around 100 degrees C associated with the transition from the alpha to the beta phase only in the ECO material. In accordance with previous work, it is found that the alpha/beta ratio is the highest for the ECO polymer and decreases with increasing propene content in EPCO polymers. Above 2.9 mol% of propene incorporation, EPCO polymers show exclusively beta phase. Heat of fusion (degree of crystallinity) and melting point decreased with increasing propene level, as expected. Accordingly, crystalline density (as determined by WAXS) and lattice interchain interaction las determined by Raman) were also found to decrease by increasing the propene incorporation. (C) 2000 Elsevier Science Ltd. All rights reserved.