title: New liquid crystalline materials based on two generations of dendronised cyclophosphazenes.
abstract: A divergent approach was used for the synthesis of dendritic structures based on a cyclotriphosphazene core with 12 or 24 hydroxyl groups, by starting from [N(3)P(3)(OC(6)H(4)OH-4)(6)] and using an acetal-protected 2,2-di(hydroxymethyl)propionic anhydride as the acylating agent. Hydroxyl groups in these first- and second-generation dendrimers, G1-(OH)(12) or G2-(OH)(24), were then condensed in turn with mono- or polycatenar pro-mesogenic acids to study their ability to promote self-assembly into liquid crystalline structures. Reactions were monitored by using (31)P{(1)H} and (1)H NMR spectroscopy and the chemical structure of the resulting materials was confirmed by using different spectroscopic techniques and mass spectrometry (MALDI-TOF MS). The results were in accordance with monodisperse, fully functionalised cyclotriphosphazene dendrimers. Thermal and liquid crystalline properties were studied by using optical microscopy, differential scanning calorimetry and X-ray diffraction. The dendrimer with 12 4-pentylbiphenyl mesogenic units gives rise to columnar rectangular organisation, whereas the one with 24 pentylbiphenyl units does not exhibit mesomorphic behaviour. In the case of materials that contain polycatenar pro-mesogenic units with two aromatic rings (A4 vs. A5), the incorporation of a short flexible spacer connected to the periphery of the dendron (acid A5) was needed to achieve mesomorphic organisation. In this case, both dendrimer generations G1 A5 and G2 A5 exhibit a hexagonal columnar mesophase.
authors.affiliation: Departamento de Química Inorgánica, Facultad de Ciencias, Instituto de Síntesis Química y Catálisis Homogénea, Universidad de Zaragoza, Spain. jjimvil@unizar.es
authors.forename: Josefina
authors.initials: J
authors.lastname: Jiménez
authors.forename: Antonio
authors.initials: A
authors.lastname: Laguna
authors.forename: Elena
authors.initials: E
authors.lastname: Gascón
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Sanz
authors.forename: José Luis
authors.initials: JL
authors.lastname: Serrano
authors.forename: Joaquín
authors.initials: J
authors.lastname: Barberá
authors.forename: Luis
authors.initials: L
authors.lastname: Oriol
mesh_terms: D050091:Dendrimers / Q000138:chemical synthesis* / Q000737:chemistry; D050866:Liquid Crystals / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008859:Microscopy, Polarization; D015394:Molecular Structure; D009943:Organophosphorus Compounds / Q000737:chemistry*; D044367:Phase Transition; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014961:X-Ray Diffraction
chemical_list: D050091:Dendrimers; D009943:Organophosphorus Compounds; C074235:cyclophosphazene monomer