Temperature induced aggregation in aqueous solution of a series of PEO-PPO-PEO copolymers

The temperature induced aggregation phenomena of a series of poly(ethylene oxide)-poly(propylene oxide)poly(ethylene oxide) block copolymers (poloxamers) were investigated using dye incorporation UV spectroscopy, over a range of mass concentrations (0.1-15 mg ml(-1)). Initial experiments were performed using two different dyes (1,6-diphenyl-1,3,5-hexatriene (DPH) and I-2) so that the performance of each indicator for studying poloxamer aggregation could be determined. Subsequently, the onset temperatures (T-o) and temperature maxima (T-m) for the aggregation processes of 19 poloxamers were determined, using I-2 as an indicator. The aggregation temperature was observed to be dependent on both molecular mass and solution concentration for polymers comprising the same percent PEG, the aggregation temperature decreasing with increasing mass and/or increasing concentration. (C) 1998 Elsevier Science B.V. All rights reserved.