By employing differential staining under controlled conditions and by experiments on resist ance to chemicals, it is shown that wool possesses an inherent bilateral structure which runs the entire length of the fiber from root to tip. The similarity in behavior of wool, as shown in this study, to the formation of crimp in viscose rayon indicates that structural asymmetry may be re sponsible for the coiling and crimping nature of the wool fiber. Isolated single wool fibers show a pronounced tendency to coil; however, when movement is restricted by the proximity of other fibers in a lock or in mass, the result is the formation of crimp.

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SynopsisThe polyimides baaed on 3,3,4,4'-biphenyltetracarboxylic dianhydride (BPDA) described in Part I of this series were dissolved in p-chlorophenol and spun into fibers using a coagulating bath of ethanol. The fibers as spun had in general low tenacities and low moduli, but a heat treatment at 300-5WC under tension produced a remarkable increase in strength and modulus, and fibers with a tensile strength of 26 g/den (3.1 GPa) and an initial modulus higher than 1,ooO g/den (120 GPa) could be obtained. Thus, the annealed fibers of polyimides are comparable to aramid fibers in mechanical properties. To heating in air and in the saturated steam, the polyimide fibers showed higher resistance than the aramid fibers. The polyimide fibers surpassed the aramid fibers in resistance to acid treatment and ultraviolet (UV) irradiation, but were inferior in resistance to alkali treatment. The annealed fibers of polyimides displayed distinct X-ray diffraction patterns. The chain repeat distance of 20.5 8, determined on the fibers of polyimide prepared from BPDA and o-tolidine, and 20.6 8, determined on the fibers of polyimide derived from BPDA and 3,4diamindiphenyl ether are reasonable when the dimensions of monomeric units and the shapes of the molecular chains are considered.The X-ray reflections of both polyimide fibers were indexed satisfactorily on the basis of postulated unit cells.

synopsisPolyimides with aromatic links are synthesized usually in two steps, but a series of aromatic polyimides with large molecular weights sufficient to produce strong fibers were prepared in one step by the reaction of 3,3', 4,4'-biphenyltetracarboxylic dianhydride (BPDA) with various aromatic diamines. The one-step polycondensation wa8 possible even when BPDA was replaced to some extent by pyromellitic dianhydride, which is a basic component in the conventional two-step method. The copolyimides baaed on BPDA and mixtures of aromatic diamines were also synthesized in similar manner. For the one-step polycondensation, phenol and some of ita derivatives were found to be suitable solvents, while the typical solvent employed in the two-step method, such as N-methyl-%pyrrolidone, could not be used because of the precipitation of low-molecular weight polyimides. p-Hydroxybenzoic acid proved to be a very efficient accelerator for the conversion of polyamic acids to polyimides.