Mesomorphic properties of branched triphenylene liquid crystalline polyesters/ethers

GUTIERREZ SUBURU, MATIAS E.; CUKIERNIK, FABIO D.

Mar del Plata

Congreso; SLAP2018: XVI SIMPOSIO LATINOAMERICANO DE POLIMEROS; 2018

INTRODUCTIONHexa-substituted triphenylenes (Tp´s)-give rise to columnar mesophases (Col LC) which in some cases exhibit electric conductivity along the columnar axis. Polymerization of difunctional Tp´s have been used both to fixe Tp positions ?thus minimizing thermal fluctuations which hinder charge transport- and to increase materials processability. 1Previous work shows that polyethers present Col mesophases, although at high temperatures. On the other hand, polyesters exhibit mesophases at lower temperatures, but of more disordered type: no Col LC phases were observed. 2We synthesized here mixed polyethers/polyesters containing Tp units in the main chain, expecting they will exhibit the best features of each kind of materials. Branching was incorporated in order to further improve their thermal properties.EXPERIMENTAL METHODSCopolymerization of two kinds of Tp-containing difunctional monomers ?a diphenolic one, and a diacid one- afforded a linear polymer, PEstC11 (11: number of C atoms between Tp units, Fig. 1). Addition of X mol % of a triphenolic monomer, yielded PEstC11/X branched materials. PD was measured by GPC. Mesomorphic properties were studied by Differential Scanning Calorimetry (DSC), Polarized Light Microscopy (POM) and powder X-Ray Diffraction (PXRD). Polymer´s fibers were extruded from their Col LC phase with a home-made device; their orientation was studied by 2D-XRD. Figure 1. Polymers? repeat unit. Main chain functional groups: ester (in red) and ether (in blue).RESULTS AND DISCUSSIONAll the studied polymers exhibited Col mesophases (XRD and POM examples on Fig 2) with wide mesomorphic range (Table 1). Actual degrees of Branching (DB) agree with the proportion of Tf-triOH used. Branching increased the clearing temperature and diminished the degree of order of the lower temperature phase, in agreement with reports for non-LC branched systems. 3Table 1. Polymers? Mw, transition temperatures (ºC) and degree of branching.Polymer Mw Tm Tg Tc DBPEst C11 12113 - 41 -- 150 0PEst C11/5 12718 -- - 35 159 0.045PEst C11/10 14231 -- - 39 161 0.110Figure 2. Polymer?s PXRD patterns, POM image for Pest11/X (inset right) and 2D-XRD of a fiber (inset left)2D-XRD results shown that triphenylene?s columns are oriented along the fibers? direction. CONCLUSIONThese copolymers, the first main-chain triphenylene-based polymers showing Col LC phases at room temperature, can be mechanically oriented. 2REFERENCES1. Kumar S., Liq. Cryst. 32, 1089-1113, 20052. H. Singh, S. Kumar, S. Kumar Pal, In: V. Kumar Thakur, M. R. Kessler, editors. Liquid Crystalline Polymers Springer: Switzerland, Vol. 1, 589-5892, 2016.3. Jayakannan M. et al., J. Polym. Sci. Part A: Polym. Chem., 38, 261-268, 2000 ACKNOWLEDGMENTSWe acknowledge CONICET and UBA for financial support; S. Suarez and L. Rossi for orientation studies and N. D´Accorso for GPC and DSC measurements.