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The solubility of poly(ethyl oxazoline) in aqueous solutions was studied. The cloud point temperatures decreased in the presence of sodium chloride but increased by the addition of tetrabutylammonium bromide or dioxane. Solution‐cast films of blends of the polymer and poly(acrylic acid) were miscible, but mutual precipitation occurred in water, methanol, and dioxane. The compositions of the complexes correspond in most cases to simple molar ratios of the interacting groups. The glass transition temperatures of the complexes are higher than the values for blends of the same compositions, and the high values are attributed to hydrogen bonds acting as physical crosslinks. Complex formation also occurs when the polymer is mixed with a styrene‐acrylic acid copolymer and with low weight polymers containing phenol groups.

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Mutual precipitates of poly (N, N‐dimethyl acrylamide) and poly (4‐hydroxystyrene) were collected from dioxane, methanol, or acetone. The glass transition (Tg) temperatures of the precipitates are higher than the weight‐average values. Clear films cast from dimethylformamide solutions have lower Tg values. Complexation also occurred between poly (ethyl oxazoline) and poly (4‐hydroxystyrene) in dioxane and between poly (vinyl pyrrolidone) and poly (4‐hydroxystyrene) in methanol. Again, the glass transition temperatures of the precipitates are higher than the values for the blend films. The ΔCp values associated with the glass transitions of the complexes are smaller than those of the blends having the same compositions. Negative excess heat capacities of mixing have been observed for several precipitates.

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