CHAIN CONFORMATION OF THE TECHNORA COPOLYAMIDE

This paper describes further X-ray diffraction work on the structure of the copolyamide prepared from terephthaloyl chloride (TPA), phenylenediamine (PDA), and 3,4'-diaminodiphenyl ether (DPE). X-ray fiber diagrams of this material consist of a series of nonperiodic layer lines, and we have shown previously that these are consistent with a structure consisting of parallel chains of completely random comonomer sequence. The meridional peak positions are predicted accurately for a fully extended chain conformation, and the peak intensities are also in reasonably good agreement. However, there is a less than adequate match between the observed and calculated peak profiles, most notably that for the peak at d ≅ 2.15Å, which is predicted to be very much sharper than that observed. The latter peak has been shown to be a measure of the correlation or persistence length for the stiff chain conformation in the solid state and is predicted to be extremely sharp when the chain is modeled by a linear infinite chain of random monomer sequence. A better fit to the broader observed peak is achieved by using a model that incorporates nonlinearity of the chain conformation due to the presence of the ether and 1,3-phenylene linkages, as well as torsional variations. This has been done by defining the nonlinearity in terms of histograms of the axial advance per monomer for each monomer type, based on a survey of models of a large number of chains with sequences selected by Monte Carlo methods. It is clear that the requirements of chain packing imply highly extended conformations, and this probably involves some distortion of the bond and torsion angles in order to align the random sequences. © 1990, American Chemical Society. All rights reserved.