LYOTROPIC LIQUID-CRYSTALLINE MAIN-CHAIN VIOLOGEN POLYMERS - HOMOPOLYMER OF 4,4'-BIPYRIDYL WITH THE DITOSYLATE OF TRANS-1,4-CYCLOHEXANEDIMETHANOL AND ITS COPOLYMERS WITH THE DITOSYLATE OF 1,8-OCTANEDIOL

A series of viologen polymers based on 4,4'-bipyridyl and the ditosyla tes of trans-1,4-cyclohexanedimethanol and 1,8-octanediol was prepared by the quaternization reaction in acetonitrile. Their polyelectrolyte behavior in a common organic solvent was studied by viscosity measure ments, and their chemical structures were determined by FTIR and 1D an d 2D NMR spectroscopies. They were characterized for their lyotropic p roperties in a number of polar organic solvents by polarizing light mi croscopy and differential scanning calorimetry and for their photochro mic properties by UV-vis spectroscopy. As expected, their inherent vis cosity in methanol decreased dramatically with the increase in concent ration in the absence of an added electrolyte. Although each of these polymers contained the ionic group along the backbone of the polymer c hain, there was an array of weak ion-pair dipoles between the tosylate ion and the 4,4'-bipyridinium ion in each of them, which was indicate d by the appearance of symmetric stretching band of S=O at a lower fre quency (1034 cm(-1)) when compared with that of -SO3Na (1064 cm(-1)) i n its IR spectrum. The aromatic protons of 4,4'-bipyridinium ion in ea ch of these polymers exhibited three pairs of signals as opposed to a pair of doublets that generally occurs in small molecules containing t his ion. These three pairs of signals were related to the structure an d dynamics of these ionic polymers in a polar solvent such as methanol , which were studied by DEFT, H-1-H-1 COSY, and NOESY spectroscopies. Each of them showed a lyotropic lamellar phase in methanol, ethanol, e thylene glycol, diethylene glycol, glycerine, and benzyl alcohol. Thei r critical concentrations (C values) were as low as 5 wt % and as hig h as 20-40 wt %, and their concentrations for the development of fully grown lyotropic phase were as low as 10-20 wt % and as high as 40-50 wt % in various alcohols depending on the polarity of the solvents, th e hydrophilicity and hydrophobicity of the solvents, and the microstru ctures of these polymers. Additionally, their lyotropic solutions in e ither glycerine or benzyl alcohol, oh irradiation with UV light, produ ced a deep blue color in the presence of air, but in absence of both a photosensitizer and a sacrificial donor. This deep blue solution had two absorption bands at 390 and 608 nm, which are the characteristic a bsorption bands of the viologen cation radical. The generation of this blue color occurred due to the photoreduction of the 4,4'-bipyridiniu m moiety via the electron transfer from the tosylate counterion.