This study examined the adsorption isotherm behavior within a homologous series of fluorescently end-labeled hydrophobically end-modified ("fluorophobe") poly(ethylene oxide)s (PEOs) on hydrophobic polystyrene (PS) latex. Results were then compared with a model for the adsorption of end-modified chains and previous adsorption studies of associative thickeners, PEOs containing hydrophobes on both ends in addition to regularly spaced weak internal hydrophobes. For both PEO series, an increase in end-group hy drophobicity yielded higher isotherm plateau coverages by up to a factor of 5 over control samples without end hydrophobes. For the fluorophobe-PEOs, an increased end-group hydrophobicity also led to a steeper slope in the low-concentration regime of the isotherm, reflecting the influence of the end group on the net adsorption energy (to the extent that the initial isotherm slope reflected an equilibrium partitioning between the interphase and the bulk). In contrast for the associative thickeners, the impact of end-group hydrophobicity on the initial isotherm slope was not apparent, and the initial slopes for the associative thickeners were generally much steeper than for any of the fluorophobe PEOs. These differences in isotherm shapes were thought to reflect differences in the molecular architecture between the fluorophobe-PEO and associative thickener series, and the impact of molecular architecture on the interaction with the substrate. In addition to altering the coverage, the end-group hydrophobes alter the interfacial morphology and the surface selectivity for specific molecular weight populations within a polydisperse PEO sample.