X-ray analysis of the structure of HM50 copolyamide fibers (original) (raw)

Initial X-ray work is described toward determination of the structure of high-strength copolyamide fibers prepared from terephthaloyl chloride (TPA), p-phenylenediamine (PDA), and 3,4'-diaminodiphenyl ether (DPE), with a TPA/PDA/DPE monomer mole ratio of 50125125. The X-ray fiber diagrams indicate a high degree of axial orientation of the molecules, and there is some three-dimensional order, although this is not as extensive as for the 50/50/0 copolymer, poly@-phenyleneterephthalamide). A very interebting feature of the data for the 50125125 copolymer is the occurrence of a series of aperiodic meridional maxima. These are reminiscent of those reported previously (Blackwell, J.; Gutierre, G. A. Polymer 1982,23,671. Gutierrez, G. A,; Chivers, R. A.; Blackwell, J.; Stamatoff, J. B.; Yoon, H. Polymer 1983, 24, 937) in fiber diagrams of wholly aromatic copolyesters, where they arise due to structural correlations along chains of completely random sequence. We have applied a similar analysis to the copolyamide structure: the copolymer chains are modeled first as an array of points separated by the appropriate monomer lengths, and the predicted X-ray scattering is averaged over all possible monomer sequences in a nematic structure. The lengths of the DPE and TPA units depend on the torsion angles at the phenyl-ether and phenyl-amide linkages, and hence a variety of models need to be considered. We find that the best agreement between the positions of the observed maxima and those calculated for a completely random sequence is obtained when the chains have highly extended conformations. Conversion from point to atomic models for the monomers leads to good agreement for both positions and intensities of the meridional maxima. These results point to the effect of intermolecular interactions in enhancing the extended conformation in liquid crystalline polymers.