The behavior of poly(alpha-ethylacrylic acid), PEA, was studied in aqueous solutions at 25 degrees C and at a polymer concentration 0.01 mol carboxyl groups/L by conductometric, potentiometric, calorimetric, and fluorescence measurements. PEA chains were characterized for molar mass, eventual crystallinity, and tacticity. The complete thermodynamic characterization of the transition of PEA chains from a contracted to an expanded form is reported. The results show that short PEA chains are strongly associated in water. Intermolecular association is effective in the whole range of degrees of ionization of carboxyl groups and was ascribed to the formation of hydrogen bonds between un-ionized groups with a favorable contribution of the hydrophobic ethyl side groups. Molecular modeling was performed on short PEA chains, either purely isotactic or syndiotactic ones. The optimized models resulted in a "bent" or "curved" conformation for both stereoisomers and confirmed the presence of intermolecular hydrogen bonds between predominately isotactic chains.