A Fourier transform infrared study on water-induced reverse micelle formation of block copoly(oxyethylene–oxypropylene–oxyethylene) in organic solvent

The water-induced micellization of poly(oxyethylene–oxypropylene–oxyethylene) block copolymer, Pluronic L92, in p-xylene solution has been investigated by FT-IR spectroscopic technique. The OH stretching band of water has been resolved by deconvolution and Gaussian curve fitting. The solubilized water can be classified into monomer bound water, dimer bound water, free water and trapped water. Each states of water were sensitive to the water to EO molar ratio (Z). Therefore, their variations with the water to EO molar ratio (Z) have been employed for the detection of the reverse micelle formation and structural change. It showed that Pluronic L92 did not form polymolecular micelles when molar ratio water/EO (Z)<0.35. For Z<1.3, spherical micelles were formed and for Z>1.3, the micelle shape could be nonspherical. The water–EO interaction dominated at all water content. As water was added in the Pluronic L92-p-xylene system, the water–water interaction strengthened during micellization and structural change of micelle. In the meantime, the block copolymer molecules showed stronger intermolecular interaction as compared with that before transition. The micellization of Pluronic L92 in p-xylene was explained by the strengthening of the intermolecular interaction of copolymer, which introduced by the water–water interaction. The results confirm the leading role of water in the reverse micelle formation of PEO–PPO–PEO block copolymer.