Effect of the composition of pluronic copolymers on the interaction with hydrophilic modified ibuprofen

Interactions between hydrophilic modified ibuprofen (Ibuprofen-PEG800, IP800) and copolymers (poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide), PEO–PPO–PEO) were systematically investigated by nuclear magnetic resonance (NMR), dynamic light scatter (DLS), and freeze-fractured transmission electron microscopy (FF-TEM). EO19PO69EO19 (P123) and EO76PO29EO76 (F68) were chosen to explore the effect of chain lengths of copolymers on the interaction by comparison with EO100PO65EO100 (F127) previously studied by us. For P123 with shorter PEO chains compared to F127, the general microstructural transition of P123/IP800 complex was quite similar to F127 irrespective of the initial conformation state of the copolymer. In P123 micelle dominated solutions, it was found that about 13 IP800 molecules were required to disarrange P123 micelles, while about 7 sufficed to disrupt F127 micelles. For F68 with shorter PPO chains compared to F127, there were no loosely coiled aggregates formed in F68 unimer dominated solutions. In the intermediate state of F68 aggregation, an increase of IP800 concentration or temperature induced the formation of the loose F68 micelle/IP800 complex, and eventually disintegrated the complex to form small complex as several IP800 molecules adsorbing on F68 unimers while the complexes with a skeleton of IP800 micelles and copolymer chains threading through were formed in F127 and P123 systems.