Study On The Synthesis And Mesomorphic Properties Of Triphenylene-based Main Chain Discotic Liquid Crystalline Polymers

Four series of triphenylene-based main chain discotic liquid crystalline polyethers Pa,b-n by changing the spacer length(n= 8-12, n standing for the methylene number) and varying the substitution positions(a,b- = 2,3-, 2,6-, 2,7-, or 3,6-, a,b- standing for the substitution positions) were designed and synthesized. 1H-NMR and FT-IR were used to determine the chemical structures of these compounds. Gel permeation chromatography(GPC) was used to determine molecular weights(MWs) and polydispersity index of these polymers. The thermal properties of these polymers were studied by differential scanning calorimetry(DSC). Polarized light microscopy and one-/two-dimensional wide-angle X-ray diffraction analysis(1D/2D WAXD) were used to examine the phase structures. Time-of-flight(TOF) method was used to investigate the charge carrier mobilities. P2,3-n had relatively low MWs(Mn < 5000) due to the intensive cyclization effects of 2,3-positions, Pa,b-n(a,b-= 2,6-, 2,7-, 3,6-) displayed odd-even variations of MWs dependent on the spacer lengths, and Pa,b-10 with the spacer length twice that of side chains of triphenylene moieties had the highest MWs(20000) in each series. Combining with DSC and POM, The characteristic polymer liquid crystalline sandy textures and order hexagonal columnar phase(Colh) with the typical XRD peaks prevailed in these polymers. The XRD results of P2,6-n, P2,7-n, P3,6-n indicated that Pa,b-10 displayed the highest order when the spacer length was twice that of the side chains. The charge carrier mobilities of Pa,b-10, namely P2,3-10, P2,6-10, P2,7-10, and P3,6-10, were measured via TOF and calculated to be 3.0 ? 10-4 cm2 V-1 s-1, 1.8 ? 10-4 cm2 V-1 s-1, 7.8 ? 10-5 cm2 V-1 s-1, and 1.9 ? 10-3 cm2 V-1 s-1, respectively. The charge carrier mobility of P3,6-10 was higher 1?2 magnitude than that of the other polymers, exhibiting the highest order.