Semiflexible liquid crystalline tetramers as models of structurally analogous copolymers

The synthesis and characterization of a series of liquid crystal tetramers is reported. These consist of molecules containing four liquid crystal units connected via three flexible alkyl spacers. The length of the central spacer is held at six methylene units, while that of the outer spacers is varied from three to twelve units. All the tetramers exhibit an enantiotropic nematic phase. The transitional properties exhibit a strong dependence on the length and parity of the outer flexible spacers. The properties of this series are compared to those of the corresponding series containing a pentamethylene central spacer. This change has a smaller than anticipated effect on the transitional properties and suggests that the four mesogenic units in the tetramer are not strongly correlated. The behavior of the tetramers is shown to strongly resemble that of a copolymer series containing differing lengths of spacers.