Scaling exponent and dispersity of polymers in solution by diffusion NMR

Nathan H Williamson; Magnus Röding; Stanley J Miklavcic; Magnus Nydén

doi:10.1016/j.jcis.2017.01.058

Scaling exponent and dispersity of polymers in solution by diffusion NMR

J Colloid Interface Sci. 2017 May 1:493:393-397. doi: 10.1016/j.jcis.2017.01.058. Epub 2017 Jan 18.

Authors

Nathan H Williamson¹, Magnus Röding², Stanley J Miklavcic³, Magnus Nydén⁴

Affiliations

¹ Future Industries Institute, University of South Australia, Mawson Lakes, SA 5095, Australia. Electronic address: nathan.williamson@mymail.unisa.edu.au.
² SP Agrifood and Bioscience, Frans Perssons väg 6, 402 29 Göteborg, Sweden; School of Energy and Resources, University College London, 220 Victoria Square, Adelaide, SA 5000, Australia. Electronic address: magnus.roding@sp.se.
³ Phenomics and Bioinformatics Research Centre, School of Information Technology and Mathematical Sciences, University of South Australia, Mawson Lakes, SA 5095, Australia. Electronic address: m.nyden@ucl.ac.uk.
⁴ Future Industries Institute, University of South Australia, Mawson Lakes, SA 5095, Australia; School of Energy and Resources, University College London, 220 Victoria Square, Adelaide, SA 5000, Australia. Electronic address: m.nyden@ucl.ac.uk.

PMID: 28131085
DOI: 10.1016/j.jcis.2017.01.058

Abstract

Molecular mass distribution measurements by pulsed gradient spin echo nuclear magnetic resonance (PGSE NMR) spectroscopy currently require prior knowledge of scaling parameters to convert from polymer self-diffusion coefficient to molecular mass. Reversing the problem, we utilize the scaling relation as prior knowledge to uncover the scaling exponent from within the PGSE data. Thus, the scaling exponent-a measure of polymer conformation and solvent quality-and the dispersity (M_w/M_n) are obtainable from one simple PGSE experiment. The method utilizes constraints and parametric distribution models in a two-step fitting routine involving first the mass-weighted signal and second the number-weighted signal. The method is developed using lognormal and gamma distribution models and tested on experimental PGSE attenuation of the terminal methylene signal and on the sum of all methylene signals of polyethylene glycol in D₂O. Scaling exponent and dispersity estimates agree with known values in the majority of instances, leading to the potential application of the method to polymers for which characterization is not possible with alternative techniques.

Keywords: DOSY; End-group analysis; Flory exponent; Gamma distribution; Lognormal distribution; Molar mass; Molecular weight distribution; Nuclear Magnetic Resonance spectroscopy; Polydispersity Index; Polymers; Pulsed field gradient; Pulsed gradient spin echo; Scaling law; Self-diffusion.

Publication types

Research Support, Non-U.S. Gov't