We have characterized the association behavior of a series of randomly hydrophobically-modified poly(N,N-dimethylacrylamides) having different molecular weights and different degrees of hydrophobic modification with the hydrophobic modifier octadecylpyrene. The extent of association between hydrophobes was quantified using fluorescence spectroscopy to measure excimer/monomer ratios. The consequences of this association for the diffusion of the polymer chains were measured using the pulsed-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR) technique. In general, higher degrees of hydrophobic modification cause higher polymer association probabilities. Specifically, at low degrees of hydrophobic modification the associations are primarily intermolecular at all concentrations, while at high degrees of hydrophobic modification there is a crossover from primarily intramolecular to primarily intermolecular associations with increasing concentration. Network formation does not occur within the range of concentration investigated, probably because the substantial hydrophobicity of these particular hydrophobic modifiers favors smaller aggregates. In the concentration regime where intermolecular associations dominate, the most hydrophobic associating polymers form clusters consisting of four macromolecules on average.