Mesomorphic properties of new tripheylene-based polyesters and their monomers

FLORENCIA CECCHI; BERTRAND DONNIO; DANIEL GUILLON; FABIO D. CUKIERNIK

Maribor

Congreso; XI EUROPEAN CONFERENCE ON LIQUID CRYSTALS; 2011

            Substituted triphenylenes have been widely studied as discotic mesogens. They form nematic and columnar mesophases [1]  with potential applications in1-D charge migration due to the p-p interactions between the aromatic cores [2], with the advantage that they can be easily processed. However, the lack of long-range order along the column limits the charge-carrier mobility [3]. To improve this property it is necessary to obtain macroscopically aligned and stable monodomains of these materials. The introduction of covalent bonds between mesogens might reduce rotational disorder of the aromatic core around the columnar axis. In this context, some triphenylene-based main chain polymers have already been studied [4]:  for example, Ringsdorf et al. [5] and Shimizu et al [6] have reported the synthesis of polyesters employing protected dihydroxy triphenylenes (substituted in positions 2,6-2,7 and 3,6 respectively)   and á,w-diacids as co-monomers.  In this work two new polyesters were obtained by copolymerization of ethylene glycol with tetrakis(hexyloxy) triphenylenes containing carboxylic groups as terminal substituents of the other alkoxy chains, located at positions 2 and 7. The two studied  materials differ in the length of the alifatic chain bearing the terminal carboxylic groups. Both monomers and polymers were characterized by 1H-NMR, 13C-NMR, FTIR, MALDI-TOF and elemental analysis; GPC was also used for polymers. The liquid cristalline (LC) properties were studied by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). Both polymers exhibited thermotropic mesomorphism near room temperature, while only one monomer showed LC behaviour from 70 to 90°C. A comparison with the previously reported polymers will be made in terms of the positions of the carboxilic groups relative to the cores and in terms of the position of the polymer chain linker. [1] S. Kumar S, Liq. Cryst. 31,1037-1059 (2004) [2] N. Boden , B. Movaghar. Handbook of Liquid Crystals: Wiley-VCH: NY; Vol 2B, Chapter IX, pp 781-798 (1998) [3] R. J. Bushby,O. R. Lozman, Curr. Opin Solid state Mat. Sci. 6,569 (2002) [4] S. Kumar. Liq. Cryst. 1089-1113 (2005) [5] W. Kreuder, H. Ringsdorf, P. Tschiner. Makromol. Chem.. rapid Commun. 6, 367 (1985) [6] W. Wan, H. Monobe, Y. Tanaka,Y. Shimizu. 5, 571 (2003)