Quantitative estimation of the degree of derivatization: an alternative methodology using 1-D and 2-D NMR experiments

The precise estimation of the degree of derivatization of functional groups in polymers is important for determining their macroscopic properties. In this work, the quantitative estimation of the extent of esterification of novolac copolymers with di-tert-butyl dicarbonate was studied. Although the extent of esterification has been calculated previously by quantifying the signals from FT-IR and UV-Vis spectroscopy, these were restricted to monitoring the progress of the derivatization process. The 13C NMR signal intensities from the inverse-gated 1H-decoupled NMR spectrum have been used recently for the quantitative estimation of the degree of esterification of polymers. An alternative methodology has been suggested by us based on the fully relaxed 1H chemical shift intensities. However, since the proton signals of novolac resins are generally broad and overlapping, the proton decoupled 13C NMR spectrum was used to identify the 1H NMR signals using the 2-D HSQC technique. A TOCSY experiment was also performed to confirm further the 1H NMR signal assignments and, finally, the deconvoluted 1H NMR spectrum was used for the calculation of the extent of derivatization.