Dense permselective membranes were prepared from two series of polydimethylsiloxanes (PDMS) bearing fluorinated groups and acrylic or vinyl ether type photocrosslinkable groups linked to the polysiloxane chain through urethane bridges.These dense permselective membranes were evaluated for their application as gas permeation membrane for the purification of natural gas. Permeabilities and selectivities towards the CO2/CH4 gas pair were measured.This study showed that the selectivity increased with the introduction of C8F17 fluorinated groups and/or acrylic groups. (C) 2003 Elsevier Science B.V. All rights reserved.