Poly(propyleneimine) Liquid Crystal Codendrimers Bearing Laterally and Terminally Attached Promesogenic groups

The synthesis, chemical characterization, and liquid crystalline behavior of two new series of poly (propyleneimine) (DAB) codendrimers are described. Both series were obtained by grafting onto the fourth -generation dendrimer (DAB-(NH2)32) various proportions of two types of promesogenic units: one of them laterally attached and the other terminally attached. Both series differ in the terminally attached promesogenic unit, being chiral in series 1 and achiral in series 2. X-ray diffraction studies show that these compounds exhibit nematic or lamellar mesophases. For intermediate proportions, the smectic C mesophase, which was not exhibited by the homodendrimers, appears. Thus, the evolution between a nematic and an orthogonal lamellar mesophase occurs through a tilted mesophase. The chiral centers in series 1 permit the appearance of chiral nematic (N*) and chiral smectic C (SmC*) mesophases, which are studied. Deuterium NMR experiments reveal that the nematic formed by one codendrimer is uniaxial and not the anticipated biaxial nematic.