A new method to prepare membrane adsorbers with structure variations of functional polymer brush, the initiator entrapping method via photo-initiated surface-selective graft-copolymerization was used in this work. Functional polymer brush structures on polypropylene (PP) microfiltration membrane pore surfaces were obtained by using acrylic acid (AA) as functional monomer. Copolymerization of AA with "diluent" monomer acryl amide (AAm) and "crosslinker" methylene bisacrylamide (MBAA) was done for variations of the grafted layer. Characterization had been done by measurements of reversible protein binding (lysozyme, Lys), stepwise change of a high concentration buffer solution to a low one having the same pH value (inadvertent pH transient) and breakthrough curves for Lys. Membrane adsorber grafted with functional monomer AA was used as reference, membrane adsorber grafted with the mixture of functional and diluent monomers (AA/AAm) show low amount of protein binding and low inadvertent pH transient value as well as early and broad breakthrough curve, while membrane adsorber grafted with a mixture of functional and crosslinker monomer (AA/MBAA) show high amount of protein binding and high inadvertent pH transient value as well as late and sharp breakthrough curve. Structure variations of the grafted functional polymer brush membrane adsorber with crosslinker monomer (AA/MBAA) show the lowest axial dispersion and thus also increase the efficiency of adsorbent utilization.