Two families of liquid crystal dendrimers consisting of a dendrimeric core [fourth and fifth generations of poly(amidoamine) (PAMAM) and poly(propyleneimine) (DAB)] and several large-sized mesogenic units (incorporating three, six, and nine terminal alkoxy chains) have been prepared. The study of these materials reveals the existence of a hexagonal columnar mesomorphism in all cases. We propose a model to explain this behavior based on theoretical calculations made from experimental X-ray diffraction data. The plasticity of the dendrimeric cores, related to their conformational freedom, allows the macromolecules to adopt a cylindrical shape in which the mesogenic units are accommodated around the central core. As a result of this cylindrical symmetry of the molecules, a supramolecular columnar arrangement is present in the mesophase. A complete degree of functionalization of some of the dendrimers would prevent the appearance of a columnar mesophase according to our model. However, we have found that, in all cases, the number of promesogenic units attached to the dendrimer cores is lower than that possible, which permits the cylindrical arrangement of the macromolecules and the existence of columnar mesomorphism.

This work has been supported by the CICYT of Spain and the FEDER funds (E. U.) under the Projects MAT2002- 04118-C02-01 and MAT2003-07806-C01, by the European Union under the RTN Project “Supermolecular Liquid Crystal Dendrimers (LCDD)” (HPRN-CT2000-00016), and by the Diputación General de Aragón. R.M.R. acknowledges a fellowship from the Ministerio de Educación y Ciencia (Spain).

6 pages, 3 figures, 4 tables, 1 appendix.-- Supporting Information Available: http://pubs.acs.org.

Peer reviewed