Poly(propyleneimine) liquid crystal codendrimers bearing laterally and terminally attached promesogenic groups

Martín-Rapún, Rafael, Marcos, Mercedes, Omenat, Ana, Serrano, José-Luis, Luckhurst, Geoffrey R. and Mainal, Azizah (2004) Poly(propyleneimine) liquid crystal codendrimers bearing laterally and terminally attached promesogenic groups. Chemistry of Materials, 16 (24), 4969-4979. (doi:10.1021/cm049191l).

Abstract

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 I 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.

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