The structure of a cyanobiphenyl side chain liquid crystalline poly(silylenemethylene)

The structure of a side chain liquid crystalline poly(silylenemethylene) (–(SiCH3R–CH2)–: R=O(CH2)11O–Ph–Ph–CN, Ph=phenyl) (CN-11) has been studied by X-ray diffraction and differential scanning calorimetry (DSC). The DSC results showed that CN-11 has transitions at ∼92 °C (T2) and ∼147 °C (T1) during both cooling and immediate heating. A third transition occurred at ∼50 °C (T3) during heating after annealing at room temperature. The X-ray fiber pattern of the CN-11 annealed at room temperature showed several wide and small angle reflections which were indexed by a monoclinic unit cell with parameters a=16.8 Å, b=7.42 Å, c=43.6 Å and β=102.1° (b: fiber direction), representing a crystal structure with layer thickness of ∼43 Å. Upon heating at T3, the crystal structure became less ordered (but somewhat more ordered than smectic A (SA) and smectic C (SC)). This was followed by SA (or SC) phase at T2, and ultimately an isotropic state (I) at T1. The observed layer thickness (∼43 Å) is about ∼1.5 times the most extended side chain length, indicating a double-layer structure with tilted or interdigitated side chains. The X-ray fiber pattern had a four-point pattern at d=4.52 Å, suggesting that the side chains in the crystal are likely to be tilted by 56° from the polymer fiber axis.