Synthesis and thermal behavior of telechelic poly(butadiene)diols with azobenzene-based liquid-crystalline units in side chains

Mesogenic thiols with azobenzene as a rigid part and with various substituent (H-, methoxy-, butoxy- or octyloxy-) in para-position of azobenzene ring were synthesized by multi-step syntheses. The thiols were grafted onto double bonds of telechelic poly(butadiene)diol (Mn ~ 2,400, functionality fn = 2, 60 mol.% of 1,2-butadiene units) via radical addition in the presence of 2,2′-azobis(2-methylpropionitrile) (AIBN). Initial mole ratio of thiol/double bonds varied in the range of 0.2–1.0. Influence of the azobenzene substituent on the extent of modification reaction was estimated using elemental analysis, size-exclusion chromatography and 1H NMR spectroscopy. The substituent on mesogen plays also an important role in thermal behavior of both the thiols and the obtained comb-like polymers, as determined by differential scanning calorimetry and polarizing optical microscopy.