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Photosensitive Ionic Nematic Liquid Crystalline Complexes Based on Dendrimers and Hyperbranched Polymers and a Cyanoazobenzene Carboxylic Acid

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journal contribution
posted on 26.08.2008, 00:00 by Mercedes Marcos, Rafael Alcalá, Joaquín Barberá, Pilar Romero, Carlos Sánchez, José Luis Serrano
The synthesis and characterization of ionic liquid crystal dendrimers and hyperbranched polymers based on the ammonium salts of commercially available dendrimers poly(propylene imine) [PPI-(NH2)n] (with n = 16), and poly(amidoamine) [PAMAM-(NH2)n] (with n = 16), and random hyperbranched poly(ethyleneimine) (PEI) and the prepared fully methylated PEI (namely PEIMe) with 5-(4-cyanophenylazophenyloxy)pentanoic acid (CAzPA) are reported. The occurrence of proton transfer from the carboxylic acid to the amine groups was confirmed by IR and NMR measurements. 5-(4-Cyanophenylazophenyloxy)pentanoic acid does not show mesogenic properties. However, all synthesized ionic complexes displayed a nematic mesophase. The liquid crystalline behavior was investigated by means of differential scanning calorimetry, polarizing light optical microscopy, and X-ray diffractometry. Themogravimetry analysis was carried out in order to determine the stability of the complexes, all of which have their mesophase−isotropic liquid transition under the temperature of 5% weight loss. Birefringence has been induced using 488 nm linearly polarized light in thin films of the ionic dendritic polymers containing azobenzene moieties. High and stable values of the in-plane order parameter up to 0.67 have been reached.