Molecular orientation in liquid fibers of nematic polymers

The degree of macroscopic orientation of molten fibrous samples of nematic semiflexible polymers has been investigated by x-ray diffraction. Melting of highly oriented fibers is followed by a partial loss of macroscopic orientation but does not produce collapse of the fiber. The residual orientational order remains unaltered for a considerable time. The degree of orientational order depends on the temperature and undergoes odd-even fluctuations according to the parity of the number of carbon atoms contained in the flexible part of the monomer unit. Extrapolation of the order parameter to the isotropization temperature leads to a value of about 0.63 for even-type polymers and to about 0.47 for odd-type polymers. An intermediate value is found for a copolymer containing equal amounts of even and odd monomer units along the polymer chain.