Please login first
Evaluation of reactivity (pKa) of substituted aromatic diamines, monomers for polyamides synthesis, via Nuclear Magnetic Resonance, NMR-1H
* 1 , 2 , 3 , 3
1  Technical University of Esmeraldas. Campus New Horizons. Faculty of Science & Technology, Chemical Engineering Coordination and Multidisciplinary Research Group-GIM-FACI. Esmeraldas, Republic of Ecuador
2  Universidad de las Américas, UDLA, Facultad de Ciencias de la Salud. Udla-Park, Quito, Ecuador
3  Technical University of Esmeraldas. Campus New Horizons. Chemical Engineering Coordination. Esmeraldas, Republic of Ecuador


Determining the relationship between properties of aromatic polyamides and the structure of monomers allows modeling and designing the synthesis of polymers with special properties, from dialysis membranes, ion exchange systems, to thermo-resistant materials and impact protection devices. A singular dependency is observed when investigating aromatic diamines-type monomers, specifically their basicity, which constitutes one of the fundamental criteria for evaluating their reactivities or reaction capacity under catalytic conditions to generate special polymers. Nuclear Magnetic Resonance (250MHz NMR-1H, in CaCl2-added dimethylformamide) is a very useful and versatile analytical tool for such purposes. The direct dependence between the magnitude of the chemical shifts (d, ppm) of the protons of the amino groups (NH2-) and the pKa values ​​is demonstrated in the case of substituted aromatic diamines substituted with ionogenic functional groups (-COOH, -SO3H). Based on the obtained equation (pka = 13.1512 – 1.67039 x d (ppm)), and on the experimental data of the values ​​of d, ppm, the basicity of the primary amino groups, which characterize the reactivity of the monomers at the initial moment of the interphasic poly-condensation, can be calculated and selectively modify some properties of polyamides to optimize their rational use and effectiveness. The similar conside-ration for correlating chemical shift and net charge on nitrogen atom was taking into account and an obtained equation also correlates significantly (chemical shift (d, ppm) = -7.0593 – (37.57628 x φ). Aromatic diaminas were synthetized according established protocols and statistical-molecular studies were developed using Hyperchem pack-2005 and Mopac-6.

Keywords: aromatic amines, NMR-1H, reactivity, pKa