NMR Characterization of Polyethylene Glycol Conjugates for Nanoparticle Functionalization

The molecular weight, purity, and functionalization of polyethylene glycols are often characterized by H-1 NMR spectroscopy. Oft-forgotten, the typical H-1 NMR pulse sequence is not C-13 decoupled. Hence, for large polymers, the 13C coupled H-1 peaks arising from the repeating units have integrations comparable to that of the H-1 of the terminal groups. Ignoring this coupling leads to erroneous assignments. Once correctly assigned, these C-13 coupled H-1 peaks can be used to determine both the molecular weight of the polymer and the efficacy of conjugation of a terminal moiety more accurately than the uncoupled H-1 of the repeating unit.

Automated summary

The molecular weight, purity, and functionalization of polyethylene glycols are commonly determined using H-1 NMR spectroscopy. It is important to consider the C-13 coupling in the H-1 NMR pulse sequence for large polymers, as the integrations of the 13C-coupled H-1 peaks from the repeating units can be similar to those of the H-1 peaks from the terminal groups. Ignoring this coupling can lead to incorrect assignments. Once appropriately assigned, these C-13-coupled H-1 peaks can provide more accurate measurements of the polymer's molecular weight and the efficacy of conjugation of a terminal moiety than the uncoupled H-1 peaks from the repeating units.