Nuclear Magnetic Resonance Measurements of Molecular Weights

Alternative Title

Self-diffusion of poly(methyl methacrylate) in acetonitrile


The pulsed-gradient spin-echo NMR technique has been used to study the self-diffusion of both monodisperse and polydisperse poly(methyl methacrylate) (PMMA) in 5 wt % solutions in acetonitrile-d3 at 40°C. The spin-echo attenuation for the methoxy resonance of monodisperse PMMA is exponential and characterized by a single self-diffusion coefficient, D. The variation in the self-diffusion coefficient with molecular weight of the polymer follows a simple scaling law, with D = 2.5 × 10-6(M)-0.87. For polydisperse PMMA samples nonexponential decays of the spin-echo intensity are observed. By use of the experimental scaling law, the decay curves for the polydisperse polymers could be used to determine the molecular weight of the polymer. It was found that simple exponential (monodisperse), Schulz, combination, and disproportionation models for molecular weight distributions all gave reasonable estimates of the weight-average molecular weight which were consistent with those obtained from gel permeation chromatography measurements. However, the accuracy of the fits for the various molecular weight distributions is such that a weight-average molecular weight is perhaps the most that can be determined with good accuracy in these experiments. © 1987 American Chemical Society.



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© 1987 American Chemical Society (ACS), All rights reserved.

Publication Date

01 Jan 1987