Mechanically strong, anti-fouling and pH-resistant isoporous membranes prepared from chemically designed new block copolymers

Isoporous membranes with strong mechanical strength as well as good resistance to swelling and bio-fouling are highly desirable in separation applications. Unfortunately, isoporous membranes combined with all these performances have been rarely prepared as far as we know. In the current work, we tried to produce such membrane from the molecular engineering aspect by synthesizing a new block copolymer poly(hydroxypropylene)-block-polystyrene (PhPP-b-PS) from a common polymer of poly(acrylic acid)-block-polystyrene (PAA-b-PS) via the LiAlH4 mediated reduction reaction. Unlike most of amphiphilic copolymers that usually contained water-soluble polymer or polyelectrolyte as the pore forming segments, PhPP-b-PS was a new polymer with the hydrophilic while water-insoluble PhPP as the pore forming phase. When fabricating into an isoporous membrane, it showed an excellent resistance to bio-fouling due to the electroneutrality of PhPP. Besides, its water flux decreased by only ~12 % in pH ranging from 1 to 12 while flux of controlled membranes prepared from PS-b-PAA reduced by 86 % in the same region, proving the good resistance to pH induced pore swelling. This result was further demonstrated by the molecular sieving to proteins of different sizes. The mechanical strength was finally determined and compared with several well-known membranes, observing that both the elongation at break and toughness of fabricated membranes were comparable with polysulfone ultrafiltration membranes and times higher than art-of-state isoporous membranes. The superior strength of our isoporous membranes was assigned to the unique property of PhPP that tended to form tight physical cross-linking because of high-density hydrogen-bonding interaction along the chains. Results showed herein will open a new avenue for the preparation of next-generation isoporous membranes with outstanding performance from a precise designing of block copolymers with custom-made molecular structures and functionalities.