Using 1H NMR Spectra of Polymers and Polymer Products To Illustrate Concepts in Organic Chemistry

The use of 1H NMR spectroscopy to analyze the number-average molecular weight of a methoxy poly(ethylene glycol) (MPEG) and an acetate derivative of this MPEG is described. These analyses illustrate NMR principles associated with the chemical shift differences of protons in different environments, NMR integration, and the effect of the natural abundance of 13C carbons in a polymer and the resulting low but predictable intensity of the satellite peaks due to 13C–1H spin–spin coupling. Also included in this discussion is an example of end-group analysis of the product of an acetylation reaction. In the discussion of the acetylation product, an 1H NMR spectrum of a crude product mixture where the small peaks due to end groups can be seen along with a set of impurities due to catalyst, solvents, and byproducts is included because, in practice, chemists often first see these sorts of spectra.