Abstract: Composite polymer membranes are disclosed comprising a first polymeric material which defines a porous matrix, and a second polymeric material which at least partially fills, and thereby blocks, the pores of the matrix, and in which preferably each of the first and second materials are crosslinked. The membrane preferably includes a layer of an ethylenically unsaturated carboxylic acid which is graft-polymerized with the first polymeric material of the porous matrix on one of its surfaces. Crosslinking has been found to improve the transport characteristics of species through the membrane, such as the barrier performance of the membrane towards species dissolved in solution.

Abstract: A composite membrane comprises a first material which defines a porous matrix and a second material blocking the pores of the matrix, the second material having been crosslinked by irradiation, preferably with UV radiation, when in the pores. Preferably a crosslinking agent is mixed with the second material.The porous matrix may be made by leaching a water soluble material from a blend of that material with polyethylene. The second material may be polymerizable, for example an acrylic acid derivative.

Abstract: A method of making a plugged microporous film from a film which comprises a structural component having pores extending therethrough, and a plugging material within the pores, the method comprising:(a) selectively treating the plugging material so that its susceptibility to a crosslinking treatment differs from a first region of the film to a second region thereof;(b) crosslinking the plugging material at the second region of the film; and(c) removing the uncrosslinked plugging material from the first region of the film leaving plugs of crosslinked plugging material in the pores at the second region of the film.

Abstract: An article which is rendered waterproof by a microporous membrane of a hydrophobic material, the pores of the membrane in a layer-like region on or towards a surface thereof being plugged with a hydrophilic material, leaving hydrophobic material exposed on the said surface between the pores.