Low-field 1H-NMR spectroscopy for compositional analysis of multicomponent polymer systems

The accurate characterization of relative composition in multicomponent polymer systems such as statistical copolymers, block copolymers, and polymer blends is critical to understanding and predicting their behavior. Typically, polymer compositional analysis is performed using H-1 Nuclear Magnetic Resonance (NMR) Spectroscopy which provides quantitative chemical group concentrations without prior calibration. This utility has led H-1 NMR spectroscopy to become a routine method for the molecular characterization of polymers. Unfortunately, due to cost constraints, NMR spectroscopy is rarely used for routine materials verification such as quality control in industrial settings that commonly lack on-site advanced instrumentation facilities. Recently, low-field or so-called benchtop NMR spectrometers have been introduced commercially as a less expensive alternative to higher field, and costlier, NMR spectrometers. Here, we examine the capability of a low-field H-1 NMR spectrometer (60 MHz) for the compositional analysis of select block copolymers and polymer blends by direct comparison with results obtained using a 400 MHz NMR spectrometer. In the analysis of high 1,4-content polyisoprene we find quantitative agreement between the 400 and 60 MHz spectrometers. Furthermore, quantitative agreement is demonstrated for compositional analysis of commercially available poly(styrene-b-isoprene-b-styrene) (SIS) and poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymers and polymer blends of polystyrene/polyisoprene (PS/PI) and polystyrene/poly(methyl methacrylate) (PS/PMMA) that also serve as proxies for statistical and block copolymer analysis. Overall, we find low-field H-1 NMR spectroscopy to be an accessible, powerful and useful tool for polymer characterization.