A side chain liquid crystalline (LC) polyacetylene with long spacers

namely

poly(11-{［(4′-heptoxy-4-biphenylyl)carbonyl］oxy}-1-undecyne) (PA9

7)

with high trans configuration was synthesized and the phase structures and transition behaviors were studied using differential scanning calorimetry (DSC)

one-and two-dimensional (1D and 2D) wideangle Xray diffraction (WAXD)and polarized light microscopy (PLM).The molecular packing was simulated by Materials Studio (Accelrys) and the energy was minimized using Smart Minimizer incorporated in the Discover Molecular Simulation Program.The long spacer of PA-9

7 decouples the side chain mesogen and the rigid polyacetylene backbone and results in the formation of smectic phases

but not the frustrated highly ordered smectic phase of its cousin with short spacer.DSC and 1D WAXD results showed that the sample possesses two LC phases.Based on structural results obtained from 2D WAXD experiments on oriented sample

the phase structures of PA9

7 were determined to be smectic B phase (SmB) below 70℃

smectic A phase (SmA) in the temperature ranges 70 ~ 118℃

and isotropic phase (Iso) higher than 118℃.For the SmB phase

the side chains can pack into the pseudo-long range order with hexagonal symmetry within the smectic layers.The LC phase transition of PA-9

7 follows the sequence of SmB-SmAIso.