Polymer molecular weight analysis by ¹H NMR spectroscopy

The measurement and analysis of molecular weight and molecular weight distribution remain matters of fundamental importance for the characterization and physical properties of polymers. Gel permeation chromatography (GPC) is the most routinely usedmethod for themolecular weight determination of polymers whereas matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a fast-emerging absolute, and therefore accurate, technique. Although NMR spectroscopy is one of the most powerful tools available for polymer microstructure characterization, among others, its utility in the molecular weight analysis of polymers is somewhat underappreciated. It is a reliable and more readily available teaching tool in comparison to other known techniques, such as GPC and MALDI-TOF MS, for the molecular weight determination of polymers. Demonstrated herein are the simplicity, reproducibility, and convenience of ¹H NMR spectroscopy in the analysis of polymer number-average molecular weight (M_n), using α-methoxy-ω-aminopolyethylene glycol (MPEG-NH₂) and α-methoxy-polyethylene glycol-block-poly-ε-(benzyloxycarbonyl)-L- lysine (MPEG-b-PLL(Z)) as model homopolymer and block copolymer, respectively. The molecular weight data from ¹H NMR analysis are compared to those from GPC and MALDI-TOFMS.