A Solution and Molecular Study of Thermotropic Liquid Crystalline Cellulose Derivatives

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Fully substituted cellulose ethers(tri-O-hepty1 and tri-O-decy1 celluloses)and a cellulose ester(cellulose tridecanoate)were prepared and fractionated into a number of fractions with a reasonably narrow molecular weight distribution(Mw/Mn = 1.1 - 1.3). Viscometric, light scattering, and ultracentrifugation analyses were carried out to determine the molecular parameters of those polymers. The persistence lengths P were found to be about 9.0 nm at 30ﾟC in all cases, independent of the side chain length and chemistry. A value of 5.0 X 10^<-3> was obtained for the temperature coefficient alpha of the heptyl ether(alpha= dln P/dT).The mesomorphic to isotropic phase transition temperatures T_i of the ethers and esters in the bulk were determined as a function of the main-chain length, and compared with the theoretical prediction. This theory was formulated for a system of worklike cylinders with no intermolcular interactions but the excluded volume. The behavior of the ether derivatives closely agreed with the theoretical prediction, indicating that their mesophase(a cholesteric phase)is stabilized essentially by the excluded-volume, i. e., entropic effect and the semirigidity of the chain. The T_i points of the ester derivatives were, quantitatively, quite different from those of the ethers, which implies that their mesophase is different in origin.X-ray diffraction and infrared spectroscopic analyses of the ester derivatives showed that the oligomers, such as dimer and trimer, form a discotic columnar phase with the molecular axis normal to the column axis, and the polymers(deg. of polym. >30)form a columnar phase with the molecular axis parallel to the column axis, both phases being stabilized by an intermolecular interaction in which the carbonyl groups participate.