(US5096586-A)      Membrane used in spen. of a component from a mixt. comprising the component, has selective permeability and comprises a layer (I) of fully dense dopable polymer(s) (II). Layer (I) has an average pore size distribution of less than 20 angstroms in dia.. Pref. polymer (II) has partially conjugated pi electron system. Pref. (II) is polyaniline, esp. in an emeraldine oxidn. state. Pref. the membrane also comprises dopant(s), in amt. to modify the permeability fo the polymer as formed. Pref. the dopant is in concn. of 0.005 to 50 mol. %, per repeating unit of the polymer, and is pref. Lewis- or Bronsted-acid, or (in)organic ion.    ADVANTAGE -   Controls average pore size of the polymer membrane.    (JP6500263-W)      Membrane having selective permeability comprises a layer of at least one fully dense dopable polymer, having an at least partially conjugated pi electron system, pref. polyaniline in an emeraldine oxidn. state. It also comprises at least one dopant in an effective amount to modify the permeability of the polymer, pref. selected from Bronsted acids, inorganic and organic ions, most pref. Lewis acids.    USE/ADVANTAGE -   Selectivity of the membranes is modified in situ by doping, leading to larger sepn. factors than for non doped membranes and enabling the control of sepn. of components in a mixt.; the membranes are particularly useful for selective gas sepn., esp. mixts. contg. H3, H2, CH4, CO2, Ar, O2 and N2 (claimed). The membranes may also be used to separate ions in soln., e.g. in electrochemical cells. They may also be used in processing low and medium level nuclear waste and in food and waste water treatment by reverse osmosis.    In an example, membranes were formed from polyaniline hydrochloride in the emeraldine oxidn. state, obtd. by reacting aniline hydrochloride with an oxidant soln. of ammonium peroxydisulphate, at 0 deg.C. The membranes were doped with 4M halic acid solns. then undoped with 1M aq. soln. of ammonium hydroxide. Sepn. factors of the membranes as cast (AS) and after the doping/undoping treatments (D/U) were for H2/N2 206.7 (AC) and 7532.5 (D/U), for O2/N2 9.5 (AC) and 129.9 (D/U) and for CO2/CH418.1 (AC) and 335.9 (D/U)