According to H-1 and C-13 NMR spectra, relaxations, and PFG NMR self-diffusion measurements, partially hydrophobic additives methyl-ethyl ketone (MEK), methyl-isopropyl ketone (MIPK), and methyl-t-butyl ketone (MTBK) facilitate the conformation states decrease with the increasing hydrophobicity and bulkiness of the additive. correlation time (4-9 ms) and activation energy (43-52 kJ/mol) of transition between its conformation change and subsequent self-association of the copolymer Pluronic L64. The The temperature of the first PPO self-association decreases in the same order (by 4 K for MTBK). The interaction of the additives was indirectly proved by the decrease of their rotational and translational mobility in the presence of L64. The rotational correlation time tau(c) is between 3 and 6 X 10(-11) s, whereas that of the same molecules in the absence of L64 is lower than 6 X 10(-12) s. The normalized self-diffusion coefficient decreases to about 0.7 of its original value in the presence of L64. The interaction of the additive with the PPO block is transient but effective enough to facilitate its conformational change and self-association. Its mediation by a water molecule bound to PPO as a possible mechanism is suggested.