A novel process is being developed for the catalytic polymerization of olefins in supercritical carbon dioxide. Potential applications will mainly be in the production of EPDM and other elastomers. For this purpose, catalysts have been synthesized and tested. Late transition metal-based catalysts of the Brookhart type have been used to polymerize 1-hexene and ethylene in supercritical. CO2 yielding high molecular weight polymers. Additionally, polymerizations of 1-hexene in CH2Cl2 have been performed as reference experiments. In the case of 1-hexene, a comparison with the polymerization behavior in CH2Cl2 reveals similar molecular weights and molecular weight distributions. Furthermore, the multicomponent phase behavior of polymer systems at supercritical conditions has been studied. The phase behavior of binary and ternary systems containing poly(ethylene-co-propylene), ethylene and CO2 has been determined experimentally by measuring cloud-point isopleths. The predictions of the phase behavior as obtained from statistical associated fluid theory calculations agree very well with the experimentally determined cloud-points. Based on these results, some important aspects for the process design have been addressed, for which catalyst solubility, efficient recycle Of CO2 and purification of the polymer product are key issues.