Scaling exponent and dispersity of polymers in solution by diffusion NMR

• 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 (Mw/Mn) 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.

Ämnesord

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Nyckelord

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

Codes (symbols)

Diffusion

Diffusion in liquids

Magnetic resonance spectroscopy

Molecular mass

Nuclear magnetic resonance

Polydispersity

Probability distributions

Scaling laws

Spin polarization

Log-normal distribution

Polydispersity indices

Pulsed field gradients

Pulsed gradient spin echos

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)