Mixtures of Tertiary Amine-Functionalized Mesogens with Poly(acrylic acid)

Diethylamine-functionalized alkoxy methoxy biphenyl mesogens of variable spacer lengths (LC-1, n N, n = 5−12) and their equimolar mixtures with poly(acrylic acid) (PAA) were investigated by infrared spectroscopy, differential scanning calorimetry, polarizing optical microscopy, and X-ray diffraction. The pure LC-1, n N are polymorphic, generally possessing two different crystalline phases [a (full or partial) bilayer at ambient temperature followed by an orthogonal monolayer at higher temperatures], whose detailed characteristics depend on the spacer length. The mesogen melting point (a lamellar E-like−isotropic transition) is independent of spacer length. The equimolar LC-1, n N/PAA mixtures are biphasic, composed of a mesogen-pure phase and a phase composed of a polymer−mesogen complex resulting from proton-transfer interactions. The former is unperturbed by the presence of the latter. The complexes are liquid crystalline, most likely in the form of a partial or interdigitated smectic A mesophase. The smectic−isotropic transition temperatures are generally higher than the mesogen melting points and increase strongly with spacer length.