The development of effective antibiofouling membranes is critical for many scientific interests and industrial applications. However, the existing available membranes often suffer from the lack of efficient, stable, and scalable antifouling modification strategy. Herein, we designed, synthesized, and characterized alternate copolymers of p (MAO-DMEA) (obtained by reaction between poly(maleic anhydride-alt-1-octadecene) and N,N-dimethylenediamine) and p(MAQ-DMPA) (obtained by reaction between poly (maleic anhydride-alt-1-octadecene) and 3-(dimethylamino)1-propylamine) of different carbon space length (CSL) using a ring-opening zwitterionization. We coated these copolymers on poly(vinylidene fluoride) (PVDF) membranes using 4 self-assembled anchoring method. Two important design parameters-the CSL of polymers and the coating density of polymers on membrane were extensively examined fat their effects on the antifouling performance of the modified membranes using a series of protein, cell, and bacterial assays. Both zwitterionic, modified membranes with different coating densities showed improved membrane hydrophilidty, increased resistance to protein, bacteria, blood cells, and platelet adsorption. However, while p(MAO DMEA) with two CSLs and p (MAO DMPA) with three CSLs only differ by one single carbon between the amino and ammonium groups, such subtle structural difference between the two polymers led to the fact that the membranes self-assembled with MAO DMEA outperformed those modified with MAO-DMPA in all aspects of surface hydration, protein and bacteria resistance, and blood biocompatibility. This work provides an important structural-based design principle: a subtle change in the CSL of polymers affects the surface and antifouling properties of the membranes. It can help to achieve the design of more effective antifouling membranes for blood contacting applications.