Structure and phase determination of laterally attached side-chain liquid crystalline polynorbornenes with a 1-carbon spacer.

摘要

Most laterally attached side-chain liquid crystalline polymers (SCLCPs) synthesized thus far have exhibited only the nematic (N) phase. In order to search for laterally attached SCLCPs having a smectic C (S_C) phase, a series of polynorbornenes (PNBEs) with 1,4-bis[(3′-fluoro-4 ′-n-alkoxyphenyl)ethynyl]benzene mesogens ( n = 1–12) laterally attached to the polymer backbones through a one-carbon spacer was previously synthesized.; According to the DSC results, PNBEs (n = 9–12) exhibit three thermal events: a broad transition and two overlapped first-order transitions. For PNBEs (n = 1–12), as the number of methylene units in the side chains decreases, the broad thermal transition becomes less obvious and the separation of two transitions becomes difficult.; Wide angle X-ray diffraction experiments reveal the tilted low-angle reflections for n = 12, indicating that the mesogens organize into a tilted layer structure of a S_C phase at room temperature. The intensity and sharpness of low-angle reflections decrease with decreasing number of methylene units.; The tilt angle of low-angle reflections decreases greatly from 70°C for PNBEs (n = 9–11), and 60°C for n = 12 on heating. The tilt angle of n = 2–4 almost does not change. Therefore, the broad transition observed by DSC is associated with the change in the tilt angle.; Polarized light microscopy shows that the highest temperature ordered phase is the N phase. The lower-temperature first-order transition observed for PNBEs (n = 9–11) is a SC → N phase transition. However, the S_A phase is observed in fiber pattern of n = 12 around 85°C. The transition between the S_C and S_A phase is not first order according to DSC, and instead second order.; The plot of the scattering intensity as a function of temperature shows that the intensity sharply decreases at the temperature corresponding to the S_C → N phase transition for n = 8–11. But there is no sudden change in intensity for n = 2–7. Therefore, the phase at room temperature for n = 2–7 can be recognized as the N phase with the S_C fluctuation.