Effect of Hydrophobicity of PEO-PPO-PEO Block Copolymers on Micellization and Solubilization of a Model Drug Nimesulide

The present work explored the molecular implications governing the solubilization of a model drug nimesulide (NIM) in micelles of ethylene oxide-propylene oxide (EO-PO) triblock copolymers. The aggregation behavior and solubilization studies on four copolymers each with the same mol mass of central PPO block equal to 2,250 and varying % PEO was examined by means of UV-VIS. Moreover, high-sensitivity differential scanning calorimetry, and Fourier transform infrared spectrometry measurements were used to evaluate the critical micellization temperature. The solubilization at different temperatures (30, 37, 45 A degrees C), pH (2 to 10) and in the presence of added sodium chloride (0-2 M) was monitored and the partition coefficient (P) and the free energy of solubilization (Delta G (s) (o) ) were calculated. The site of solubilization of NIM in micelles was also probed. The NIM solubility decreased with increases in the PEO molecular weight; the drug resides in the micelle core.