Mesomorphic polyacrylates containing isomeric methyl‐substituted azobenzene mesogens

The synthesis and characterization are reported of two new series of structurally isomeric polyacrylates containing the azobenzene moiety spaced away from the backbone by a hexamethylene spacer and substituted in 4‐position with linear alkoxy groups (C₁C₆, C₁₀) and with a lateral methyl group in 2′‐ or 3′‐position. Thermal optical and X‐ray analyses of the prepared polymer samples, with molecular weight ranging from 50 × 10³ to 35 × 10⁴ Dalton (M̄_w/M̄_n = 2−3), provide evidences for the establishment of liquid crystalline behavior in the melt in a fairly broad range of temperature. In any case, quenching from the mesophase allows for the lock‐in of the liquid crystalline structure in the glassy state. The presence of the lateral methyl‐substitutents causes a drop as high as 50–100 K. in the stability of the mesophase with respect to the corresponding samples of the methyl‐unsubstituted series. A parallel depletion of the smectogenic character is also observed. Typical even‐odd effects on the isotropization temperature and relevant thermodynamic parameters have been detected along with the formation of interdigitated smectic structures.