Ionic liquid crystals derived from the protonation of poly(propylene imine) dendrimers with a cholesterol-based carboxylic acid

Abstract

The liquid crystalline character of salts resulting from the interaction of poly(propylene imine) dendrimers with 3-cholesteryloxycarbonylpropanoic acid has been studied. The supramolecular structure and consequently the observed liquid crystalline phases are dictated by the degree of protonation of primary amino groups as compared with that of tertiary ones, determined by FTIR spectroscopy in the bulk and by NMR spectroscopy in solution. Glass transition temperatures of the materials are about 38°C. At higher temperatures they are transformed to smectic C* phases while a second-order smectic C phase to smectic A phase transition is observed between 90 and 110°C depending on dendrimer generation. At about 150°C the onset of degradation is observed. The influence of the ionic dendrimeric scaffold on the thermotropic properties is discussed.