NMR ANALYSES OF ORDER AND DYNAMICS IN POLY(P-BENZAMIDE) SULFURIC ACID-SOLUTIONS/

Natural abundance NMR methods were employed to analyze static and dyna mic properties of poly(p-benzamide), the parent compound of the aramid e family of polymers, dissolved in absolute sulfuric acid. Quantitativ e determinations of order in the liquid crystal phases arising in thes e systems were carried out with the aid of bidimensional C-13 NMR data collected in the solid phase and of total line shape simulations, and the parameters thus obtained were monitored as a function of temperat ure, concentration, and polymer molecular weight. These measurements r evealed that by contrast to what had been inferred from previous macro scopic order determinations, the alignment of polymer molecules in the ir nematic domains is essentially independent of temperature. Existing measurements can still be explained in terms of a temperature-depende nt isotropic reversible arrow nematic equilibrium, whose presence and thermodynamics were unambiguously characterized by NMR. Dynamic aspect s of this interphase equilibrium as well as of the intraphase molecula r diffusion in the nematic region were explored by bidimensional and p ulsed-gradient NMR methods. Spectroscopic results were analyzed in ter ms of thermal and athermal theories predicting the appearance of nemat ic phases in rigid anisometric polymers and compared with recent NMR o bservation on other lyotropic aramide solutions.