Synthesis and phase behaviors of side-chain liquid-crystalline polymers containing azobenzene mesogen with the different length alkyl tail

A series of side-chain liquid-crystal polymers, poly[6-[4-(4-n-alkyl benzoateazo)phenoxy]-hexylmethacrylate]s (PMAzoCOORm, m=1, 2, 3, 4, 5, 6, 8, 10, 14, and 18) have been prepared by two synthetic methods. The chemical structure of the monomers was confirmed by 1H NMR and mass spectrometry. The molecular characterizations of the polymers were performed with 1H NMR and gel permeation chromatograph. The phase behaviors of polymers were investigated by the combination of techniques including differential scanning calorimetry, polarized optical microscopy, and small-angle X-ray scattering. For m=1, 2, 3, 4, 5, and 6, the polymers exhibited a monosmectic A phase in which the smectic layer period was almost identical to the side-chain length. In addition, for m=2, 3, 4, and 5, they presented the monosmectic C phase in low temperature; moreover, the tilt angle increased from 23.3 to 40.5 degrees. For m=8, 10, 14, and 18, the polymers showed a bilayer smectic A phase in which the layer spacing was larger than a fully extended side chain but less than two extended chains. On the other hand, for the clearing point, with the increasing of m, it first decreased, and then increased. All of these indicated that the length of alkyl tails played an important role in the phase behaviors of these polymers. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2759-2768