The present invention provides, in certain embodiments, a negatively charged microporous membrane comprising a porous substrate and a crosslinked coating having fixed negative charges. The crosslinked coating can be prepared, e.g., from a polymerized composition comprising an unsaturated monomer having an anionic group, an N-(hydroxymethyl)- and/or N-(alkoxymethyl)-acrylamide, a hydrophilic unsaturated monomer, and an initiator. The present invention further provides, in some embodiments, a negatively charged microporous membrane comprising a porous substrate and a crosslinked coating prepared from a polymerized composition comprising an unsaturated monomer having an anionic group, an N-(hydroxymethyl)- or N-(alkoxymethyl)-acrylamide, a polysaccharide, and an initiator. The membranes of the present invention are suitable for use in ion exchange chromatography, for example, in the separation and purification of positively charged species such as proteins.