An article that includes a functionalized copolymer and the use thereof, particularly in a process for binding biomaterials, such as in a process for separating aggregated proteins from monomeric proteins in a biological solution; wherein the article includes: a) a porous substrate; and b) a copolymer covalently attached to the porous substrate, the copolymer comprising a hydrocarbon backbone and a plurality of pendant groups attached to the hydrocarbon backbone, wherein 1) each of a first plurality of pendant groups comprises: (a) at least one acidic group or salt thereof; and (b) a spacer group that directly links the at least one acidic group or salt thereof to the hydrocarbon backbone by a chain of at least 6 catenated atoms; and 2) each of a second plurality of pendant groups comprises: (a) at least one acidic group or salt thereof; and (b) a spacer group that directly links the at least one acidic group or salt thereof to the hydrocarbon backbone by a chain of at least 6 catenated atoms; and wherein the first plurality of pendant groups are different than the second plurality of pendant groups; and wherein a mole ratio of the first plurality of pendant groups to the second plurality of pendant groups is in a range of 95:5 to 5:95.