Determination of Primary Amine Content in Bonding Agent Used in Composite Solid Propellants

The primary amine content in tetraethylenepentamine (TEPA) and TEPAN, a bonding agent used in composite solid propellants, was determined by near infrared (NIR) spectroscopy and the results were compared to those obtained by potentiometry. The band at 4930 cm⁻¹, which showed to be influenced only by primary amine groups, was chosen as the analytical band. The calibration curves based on isopropylamine (IPA) and isopropylamine/dibutylamine (IPA/DBA) mixtures proved to be suitable for determining the NH₂ content of TEPA or of samples containing mixtures of NH and NH₂ groups. It was found that TEPA contains 26.4 % of NH₂ and 25.7 % of NH, and that TEPAN contains 0.5 % of NH₂, confirming the low content of primary amine of this bonding agent. The lowest amine equivalent of TEPA is 31.1±0.3 g/eq, as determined by potentiometry, was found because this technique measures the total hydrogen content, including primary and secondary amines. The literature value of 62.6 g/eq for TEPA ACROS obtained by potentiometry in a non aqueous medium and related to the first inflection of the primary amine, validates the value obtained by NIR in this work for a similar type of amine. The equivalent weight obtained by NIR spectroscopy (62.7 g/eq) allowed to calculate the molar mass of TEPA of 195.6 g mol⁻¹, which is close to the typical value of 200 g mol⁻¹.