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 x 10(3) to 35 x 10(4) Dalton (M(w)BAR/M(n)BAR = 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-substituents 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.