Membranes that enable the recovery of organic compounds from dilute aqueous solution are desired for applications such as biobutanol production. The polymer of intrinsic microporosity PIM-1 shows promise for organophilic separations and here it is incorporated into thin film composite (TFC) membranes in order to increase the flux of permeate. Asymmetric polyvinylidene fluoride (PVDF) supports were prepared with pore sizes at the surface in the size range 25-55 nm and fractional surface porosities in the range 0.38-0.69, as determined by atomic force microscopy (AFM). The addition of phosphoric acid to the PVDF dope solution helped to control the pore size and porosity. Supports were coated with PIM-1 to form TFC membranes with active layer thicknesses in the range 1.0-2.9 mu m. Membranes were tested for the pervaporation of a 1-butanol/ water mixture (5 wt%). At 65 degrees C, values of total flux up to 9 kg m(-2)h(-1) were obtained, with separation factors up to 18.5 and values of pervaporation separation index (PSI) up to 112 kg m(-2)h(-1).