Liquid crystal elastomers containing azobenzene homologues as crosslinkers-synthesis and characterization

In this paper, we designed and synthesised three H-shaped liquid crystal monomers ABOP-n (n = 4,6,8) and a straight-chain liquid crystal monomer M. Then, we used three H-shaped liquid crystal monomers as crosslinking agents, which were graft-copolymerised with M and polymethylhydrosiloxane (PMHS), respectively, to synthesise three series of liquid crystal elastomers P-1-P-3. The products were structurally well characterised by elemental analysis, (HNMR)-H-1, and FT-IR. The phase behaviours were investigated using the polarising microscope (POM) and differential scanning calorimetry (DSC). The results showed that ABOP-8, ABOP-6, ABOP-4 and M were thermotropic enantiotropic nematic liquid crystals, exhibiting schlieren texture during heating, and spherulite texture and schlieren texture during cooling. The photochemical properties of H-shaped liquid crystal monomers were preliminarily studied by UV-Vis spectra, and it was found that they have good photosensitivity. Both the P-1-P-3 series were typical non-crystalline polymers with anisotropic coloured textures. With the increase of crosslinking monomer content, the glass transition temperature of the P-1-P-3 series both increased, while the isotropic temperature showed a trend of first decreasing and then increasing.