Synthesis and mesomorphic properties of main-chain polymers containing V-shaped bent-core mesogens with acute-subtended angle

Four achiral polymers with V-shaped bent-core mesogens in the main chain have been synthesized by polycondensation, and the effect of acute-angled central cores (Ar = 1,2-phenylene or 2,3-naphthylene) and lateral halogen substituents (X = F or Cl) was studied. All polymers were only soluble in strong acids such as H₂SO₄ and CF₃CO₂H. The solution viscosities were in the range of 0.31- 0.81 dL/g. Although polymers contained a V-shaped bent-core mesogen with acute-angled configuration in their main chain, in general they were semicrystalline in the solid state and could form smectic C phases in the melt state. However, polymer with Ar/X = 1,2-phenylene/Cl was almost amorphous. Especially, polymer with Ar/X = 2,3-naphthylene/F formed a ferroelectric smectic C phase (SmCP_F), possibly B7 phase: on ground state the spontaneous polarization was not zero (P₈ = 140 nC cm^-2), and on applying an triangular electric field a switching occurred by a collective rotation of the mesogens around the main chain axis.