EFFECT OF DRAW RATIO ON THE STRUCTURE OF AROMATIC COPOLYIMIDE FIBERS OF RANDOM MONOMER SEQUENCE

X-ray methods have been used to investigate the structure of fibers of aromatic copolyimides prepared from 3,3',4'-biphenyltetracarboxylic dianhydride (BPDA), o-tolidine (OTOL) and p-phenylene diamine (PPD). We have shown previously that the non-periodic layer lines in the X-ray fiber diagrams of these copolymers are indicative of a random comonomer sequence. In the present paper, we analyze the shifts in the layer line positions that occur with increasing draw ratio. These changes are to be understood primarily in terms of increases in the correlation lengths for the stiff chain conformation. At high draw ratios there is also evidence for the development of a more extended chain conformation, probably due to torsional variation changes in the torsion angles. It is shown that the data are sufficiently sensitive to allow quantitative analysis of these separate effects, and their dependence on comonomer ratio.