Complexes that were insoluble in water were formed by mixing aqueous solutions of a block copolymer of 2-ethtyl-2-oxazoline (EOX) and ethylene oxide (EO) and those of poly(methacrylic acid) (PMAA). The structures of these complexes were investigated by the results obtained mainly by infrared spectroscopy, X-ray diffraction, and differential scanning calorimetry. The molar ratio of MAA in the complexes was also estimated by analyzing the infrared spectra. Whereas homopolymers of EOX and EO formed nearly equimolar complexes with PMAA irrespective of the feed molar ratio, the molar ratio of MAA in the complexes formed by the block copolymer and PMAA depended on the feed molar ratio. Although the infrared spectra indicated structural differences between the homopolymer of EOX and EOX in the block copolymer before forming complexes, the spectra obtained for the complexes formed by the homopolymer and the block copolymer were similar to each other.
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