Composite gas separation membrane having a gutter layer comprising a crosslinked polar phenyl-containing - organopolysiloxane, and method for making the same -

A process for making a composite gas separation membrane comprising the following steps:

• (A) Providing a porous polyacrylonitrile structural support material having first and second surfaces, said first surface being a polyacrylonitrile surface;
• (B) Preparing a mixture comprising a polar phenyl-containing-organopolysiloxane, a crosslinker and a crosslinking catalyst;
• (C) Allowing the mixture to pre-cure but remain in an ungelled state;
• (D) Coating said first surface with said mixture and allowing said mixture to crosslink, constituting a gutter layer on the porous polyacrylonitrile structural support material, and leaving an uncoated gutter layer surface;
• and
• (E) Coating said uncoated gutter layer surface with an ultrathin 6FDA-type polyimide selective membrane layer, leaving an uncoated 6FDA-type polyimide selective membrane surface.