Abstract
1H nuclear magnetic resonance (NMR) relaxation studies of the temperature-induced micellization of a poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide), PEO−PPO−PEO, block copolymer in aqueous solution were performed in the range 280−345 K. 1H NMR spectra of the block copolymer were well resolved, thus allowing us to probe specifically the methyl and methylene relaxation processes in the PPO and PEO blocks, respectively. Interpretation of the relaxation data in terms of the Hall−Helfand correlation function leads to four distinct correlation times for the PPO and PEO blocks. The slower correlation time in the PPO block was identified as the Zimm−Rouse first normal mode of the copolymer and served to determine the hydrodynamic radius, RH, of the unimers and the micelles. On a more local scale, the behavior of the correlation time for segmental motions in the PPO block indicates an extension of the PPO chains in micelles relative to the unimers. This conformational change is related to the form...
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