Influence of alkoxy tail length on the phase behaviour of mesogen-jacketed liquid crystalline polymers with fan-shaped pendants

A series of new monomers of 2, 5-bis [(3, 4, 5-trialkoxy benzyl) oxycarbonyl] styrene (denoted as M-tri-OCmH2m + 1, m = 1, 2, 4, 6, 8, 10, 12, where m indicated the number of carbon atoms in the alkoxy group) were designed and synthesized. Then, their corresponding polymers P-tri-OCmH2m + 1 (m = 1, 2, 4, 6, 8, 10, 12) were synthesized by free radical polymerization. The chemical structure of the monomers was confirmed by elemental analysis, 1H NMR and 13C NMR. The molecular characterization of polymers was performed with 1H NMR, gel permeation chromatography (GPC). The thermal stability of polymers was investigated by thermogravimetric analysis (TGA). The phase structure and transition behaviours were studied using differential scanning calorimetry (DSC), polarized light microscopy (PLM), one- and two-dimensional (1D and 2D) wide-angle X-ray diffraction (WAXD). We found that P-tri-OCmH2m + 1 (m = 1, 2) with short n-alkoxy substituents as the tail form columnar nematic (ΦN) phase; that with the increasing length of alkoxy tails, P-tri-OCmH2m + 1 (m = 4, 6, 8) can demonstrate the hexagonal columnar (ΦH) phase; however, when the length of alkoxy tails exceeded a threshold, P-tri-OCmH2m + 1 (m = 10, 12) only develop into columnar nematic (ΦN) phase instead of ΦH phase.