Columnar mesomorphic organizations in cyclotriphosphazenes.
A synthetic strategy has been developed to prepare cyclotriphosphazenes that bear polycatenar aromatic esters as promesogenic units linked to phosphorus atoms. The microsegregation of the rigid and flexible parts of the system and the space-filling properties are the driving forces that determine the kind of mesomorphism exhibited by the organocyclotriphosphazenes. Mesogenic units that contain only one terminal alkyl chain give rise to calamitic mesomorphism, since the molecules are arranged to give a cylindrical superstructure with the aromatic promesogenic cores elongated in a manner approximately perpendicular to the cyclotriphosphazene ring. On the other hand, mesogenic units that contain three long terminal chains exhibit columnar mesophases. In this case, a discotic structure consisting of promesogenic cores arranged approximately parallel to the cyclotriphosphazene ring can explain the columnar organization. The X-ray diffraction patterns corresponding to the Col(h) mesophase of the cyclotriphosphazene with dodecyloxy chains (8) indicate the presence of helical ordering, which was confirmed for a homologous compound bearing stereogenic centers on two of the terminal chains (11). All of the synthesized phosphazenes show a high thermal stability.
Barberá
Joaquín
J
Polymer and Liquid Crystal Group--Departamento de Química Orgánica, Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-C.S.I.C., 50009 Zaragoza, Spain.
Bardají
Manuel
M
Jiménez
Josefina
J
Laguna
Antonio
A
Martínez
M Pilar
MP
Oriol
Luis
L
Serrano
José Luis
JL
Zaragozano
Irene
I
D018360:Crystallography, X-Ray; D008958:Models, Molecular; D015394:Molecular Structure; D009570:Nitriles / Q000138:chemical synthesis* / Q000737:chemistry*; D017553:Phosphorus Compounds / Q000138:chemical synthesis* / Q000737:chemistry*
D009570:Nitriles; D017553:Phosphorus Compounds; C068226:cyclotriphosphazene ester