Mixtures of a diethylamine-functionalized dodecyloxy methoxy biphenyl mesogen and poly(acrylic acid) (PAA) were investigated as a function of composition by infrared spectroscopy, differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. The data obtained indicate that the components form a monophasic supramolecular complex for amine/acid molar ratios below about 0.5 and a biphasic system composed of the supramolecular complex and a mesogen-pure phase for higher molar ratios. The complex gives rise to a smectic A mesophase that becomes isotropic at 147 degreesC for molar ratios down to about 0.3. An E-like phase is detected in the complexes of 0.4 and 0.5 molar ratios after lengthy annealing. The complex in the biphasic mixtures may also tend to E-like order below the melting point (crystal E-like-isotropic transition) of the mesogen-pure phase. The thermotropic transformation from E-like to smectic A order in the complex appears to be slow.