Synthesis, structure and mesomorphic properties of side-chain chiral liquid crystalline polysiloxanes based on (S)-(+)-2-methyl-1-butanol derivatives

The synthesis of five chiral liquid crystalline monomers (M1–M5), and their corresponding side-chain polymers (P1–P5) based on (S)-(+)-2-methyl-1-butanol derivatives is described. The chemical structures of the monomers were confirmed by FT-IR, 1H NMR, and elemental analyses. The structure-property relationships of the monomers and polymers obtained are discussed. The mesomorphic properties were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarizing optical microscopy (POM), and X-ray diffraction (XRD) measurements. All monomers showed a cholesteric phase. For M2, M3, and M5, besides a cholesteric phase and a smectic A (SA) phase, M2 also revealed an enantiotropic chiral smectic C (SC∗) phase and a monotropic smectic B (SB) phase, and M3 also showed a SB phase. The polymers P1–P5 exhibited a SA phase, moreover, P2, P3 and P5 also revealed a SC∗ phase. The experimental results demonstrated that a flexible siloxane backbone and a long flexible spacer tended to exhibit a low glass transition temperature, high thermal stability, and wide mesophase temperature range.