A strategy is outlined for building designer adsorption-based separation materials. The strategy adopts a molecule-by-molecule approach to modify surfaces with polymer films that carry out selective separations. After describing the strategy, we focus this article on preparing the foundation for these materials using self-assembly and a type of surface-confined polymerization on model gold surfaces. Experimental ellipsometry data are presented that show polymer film thickness can be tuned with sub-nanometer precision. Also presented are x-ray photoelectron spectroscopy data that support the ability to control the areal density of growing polymer chains.