The associative character of poly(ethylene oxide) (PEO) end-capped with dodecyl groups was studied by using static and dynamic light scattering and viscometry. The effect of functionalization is investigated by comparing results on unmodified PEO with PEO of the same molar mass end-capped at one or both ends. The molar mass dependence is investigated by comparing difunctionalized PEO samples with different molar masses : 10, 20, and 35 kg/mol. The experimental data are well described by a crude model which assumes open association and incorporates interparticle interaction.