All the atove findings have clearly evidenced that liquid water at temperatures near to its critical point significantly affects the course of PS degradation. It can be suggested that the presence of liquid water, as a hydrogen donor, prevents the intra-and intermolecular hydrogen transfers and the consequent shifts of the radicals sites along the polymer chain, thus decreasing the importance of secondary reactions. At the same time, the cross-linking reactions are unfavoured. Based on these promising results, we have thought to emphasize the water effect making more intiinate the phase contact between water and PS. A possible improvement was attempted by adsorbing the polymer on silica, a support with a negligible catQtic activity in the degradation of PS, as observed in previous works [l2,15] and here confirmed. Using a supported sample implies a more extended polymer area accessible to liquid water. The first preliminary runs carried out on supported PS in the ratio PS/Si l/S w/w have given the expected results. For example, operating at 320°C and 24 h the reaction has given a LP yield of 87,6*/u,a value much higher than those obtained in runs RPSH and RPS, 39.2 and 34.7%, respectively. This encouraged us to continue the investigation on the hydrous pyroiysis of PS by further improving the phase contact between the two compounds. Work is in progress in this line, also with the intention to extend the proposed technique to other polymeric substrates. Financial support by Consiglio Nazionale delle Ricerche (C.N.R.) is gratefully acknowledged. We thank Mr A. Giacumetti Schieroni for performing SEC analyses;