Molecular Organization of Poly(p-phenyleneterephthalamide) in Sulfuric Acid:  An NMR Study

Abstract

Solutions prepared by dissolving synthetic poly(p-phenyleneterephthalamide) (PPTA) in 99.8% H2SO4 were analyzed using natural abundance NMR methods as a function of the polymer concentration, molecular weight, and temperature. Concentration and molecular weight-driven transitions between isotropic, nematic, and solid-like phases could be clearly distinguished from the 13C NMR spectra of the solute and from 1H NMR spectra of the solvent. The 13C solute NMR spectra point toward a distribution in the order parameter of the liquid crystalline director and could be quantitatively reproduced using 13C shielding tensor elements measured by solid NMR in polycrystalline PPTA. Thermodynamic parameters for the nematic ⇄ isotropic equilibrium were obtained from the temperature dependence of the liquid crystalline 13C NMR spectra, and 2D NMR methods were employed to retrieve information about the kinetics of PPTA and H2SO4 migration between isotropic and nematic domains. The results obtained from these spectroscopic studies compare well with previous observations obtained using non-NMR methods; the significance of the new NMR measurements is briefly discussed.

Color Change of Sudan III against Concentrated Sulfuric Acid in Acetonitrile and Quantification for a Small Amount of Concentrated Sulfuric Acid

“…In industry, it is used in a variety of fields, such as catalysts for the production of highoctane-number trimethylheptanes 1 and biodiesel 2,3 and solvents for the production of fibers with high mechanical strength, 4 for example. On the other hand, concentrated sulfuric acid is an extremely hazardous chemical, and it sometimes causes fatal injuries.…”

A variable-director C13 NMR analysis of lyotropic aramide solutions

“…During recent years we have been exploiting some of these features to monitor via natural abundance 13 C NMR, the order of aramides in H 2 SO 4 solutions as a function of their monomeric structure. [25][26][27] An example of the features displayed by these experiments is presented in Fig. 1, which compares data recorded for the two aramide polymers poly ͑p-benzamide͒ ͑PBA͒ and poly͑p-phenylene-2,6-naphthylamide͒ ͑PPNA͒ in their respective isotropic and nematic phases.…”

Polymerization of PPTA in Ionic Liquid/Cosolvent Mixtures

“…They effectively link adjacent chains which laterally reinforces the crystal . The attractive interactions between the aromatic rings via π–π stacking could give an additional reinforcement …”

“…6 The attractive interactions between the aromatic rings via π-π stacking could give an additional reinforcement. 7 While these strong interactions between the polymer chains are beneficial for their applications, it makes PPTA on the other hand very difficult to process. In fact, not a single neutral solvent exists that is capable of keeping high-molecular weight PPTA in a dissolved state.…”