Primary Amine (−NH2) 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 imine (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.