Primary amine (-NH ₂) quantification in polymers: Functionality by ¹⁹F NMR spectroscopy

A convenient, reliable, and general method for determining the primary amine functionality of amino polymers is described. It is based on ¹⁹F NMR spectroscopy and has many advantages over known methods. The amino polymer is derivatized in situ with a reactive, trifluoromethylated aromatic aldehyde. The resultant, spontaneously formed inline (Schiff base) is then quantified by integration of its unique ¹⁹F resonance vs that of an added internal standard. The quantitative reliability of the method was first unequivocally established using a small molecule amine. Functionality determination was then demonstrated for a very broad range of polymer classes, including PS, PMMA, PEG-like, PDMS, PB, and polyamide. In contrast to, e.g., titration, this method can be carried out quickly, with small sample sizes (e.g., ca. 10 mg) and using routine NMR spectroscopic techniques.