Diffusion in Polymer Solutions: Molecular Weight Distribution by PFG‐NMR and Relation to SEC

Guo, Xiaoai; Laryea, E.; Wilhelm, Manfred; Luy, Burkhard; Nirschl, Hermann; Guthausen, Gisela

doi:10.1002/macp.201600440

Cited by 52 publications

(62 citation statements)

References 34 publications

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“…The measured signal decay was interpreted in terms of S / S 0 versus q ², where S 0 is the signal intensity at q = 0. q is defined as the product γgδ/2π, where γ is the magnetogyric ratio, and δ is the gradient pulse duration ( Table 2 ). As the data show not only the self‐diffusion of the moieties, the data processing step had to be considered, that is, the mono‐exponential Stejkal and Tanner description (Equation ) and a gamma distribution model (Equations and ) were used to describe the signal decays

\frac{s (q)}{s_{0}} = \exp [- D q^{2} (Δ - δ / 3)]

…”

Section: Methodsmentioning

confidence: 99%

Dynamics of Sodium Ions and Water in Swollen Superabsorbent Hydrogels as Studied by ²³Na‐ and ¹H‐NMR

Guo

Theissen

Claussen

et al. 2018

Macro Chemistry & Physics

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Dynamics of sodium ions and water in swollen superabsorbent polymer (SAP) hydrogels are studied by 23Na‐ and 1H‐NMR, respectively. The apparent diffusion coefficients of water in swollen SAPs, probed by 1H pulsed field gradient NMR, decreases with increasing diffusion time. The degree of hindrance depends on structural and synthesis parameters. It is quantified within a tortuosity model. Based on the results, the swelling degree has the highest impact on the ion mobility, apart from synthesis parameters leading to different levels of physical and chemical crosslinks. 23Na‐NMR relaxation and diffusion reveal the 23Na+ mobility in swollen SAPs. A higher degree of neutralization leads to faster relaxation and to a smaller apparent diffusion coefficient. Surface crosslinking restricts water mobility, but has a smaller impact on the dynamics of sodium ions. The experimental results indicate an influence of SAP structure on the dynamics of ions and water molecules.

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\frac{s (q)}{s_{0}} = \exp [- D q^{2} (Δ - δ / 3)]

…”

Section: Methodsmentioning

confidence: 99%

Dynamics of Sodium Ions and Water in Swollen Superabsorbent Hydrogels as Studied by ²³Na‐ and ¹H‐NMR

Guo

Theissen

Claussen

et al. 2018

Macro Chemistry & Physics

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“…However, the scaling parameters of Eq. (1) specific to that polymersolvent system must be found by measuring ⟨D⟩ on fractionated samples of the polymer with known M. Therefore, currently all PGSE NMR-based methods which convert from D to M cannot independently measure the absolute molecular mass distribution [12,13,14,15,16,17,18,19,20,21,22,23,24,25].In this paper we show that ν in Eq.(1) can be directly estimated from a single PGSE experiment in which the extremity (end-group) polymer signal can be spectrally resolved by a chemical shift from the polymer main-chain signal. The scaling exponent, ν, is a measure of the polymer conformation as well as solvent quality [3,26], with bounds of ν = 1/3 for a perfectly coiled, impenetrable, polymer ball and ν = 1 for a perfectly straight polymer rod [17].…”

mentioning

confidence: 99%

Scaling exponent and dispersity of polymers in solution by diffusion NMR

Williamson

Röding

Miklavcic

et al. 2017

Journal of Colloid and Interface Science

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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 D 2 O. 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:Pulsed gradient spin echo, pulsed field gradient, Nuclear Magnetic Resonance spectroscopy, Molecular weight distribution, Polymers, DOSY, Polydispersity Index, Self-diffusion, Molar mass, Flory exponent, Lognormal distribution, Gamma distribution, End-group analysis, Scaling law Synthetic polymers have distributions of molecular masses determined by their synthesis [1]. Measuring the molecular mass distribution rather than its average is important because the dispersity can influence polymer properties [2]. Absolute as opposed to relative measurements are needed when using polymer physics to fully realize the potential applications of a polymer [3]. Only a handful of techniques can measure the absolute molecular mass distribution [3]. The gold standard is size exclusion chromatography (SEC) using universal calibration [4], which does not always work [5,6]. New techniques must be developed to aid in the advancement of polymer science.Pulsed gradient spin echo nuclear magnetic resonance (PGSE NMR) [7,8] is a powerful technique for obtaining the distribution of polymer self-diffusion coefficients D [9], from which the distribution of molecular masses M can be obtained by the scaling law [10] ration give PGSE NMR a competitive edge with respect to SEC. Chemical shift information [7], e.g. in a diffusion ordered spectroscopy (DOSY) plot [11], provides the ability to observe chemical heterogeneity and impurity. Sample preparation generally does not require filtration because contaminates from large particles such as dust do not impact the experiment. However, the scaling parameters of Eq. (1) specific to that polymersolvent system must be found by measuring ⟨D⟩ on fractionated samples of the polymer with known M. Therefore, currently all PGSE NMR-based methods which convert from D to M cannot independently measure the absolute molecular mass distribution [...

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“…The question arose whether K and α are unique given that the diffusion was measured at lowest concentrations. To extend previous work, some dilute polymer solutions in CDCl 3 are summarized and the diffusion coefficients of the decamer in solution are added ( Figure ). Data are distributed around a trend line with α = 0.51.…”

Section: Resultsmentioning

confidence: 99%

“…Signal decay curves in PFG‐NMR were shown to deviate from that of monodisperse molecules in solution ( Ð M = 1), especially at larger q 2 , which provides the basis for an intuitive and effective method to quantify the dispersity. However, it is worth mentioning that for polymers with high dispersity ( Ð M ≫ 1), appropriate models such as the gamma distribution model should be used for the interpretation of NMR diffusion raw data …”

Section: Introductionmentioning

confidence: 99%

¹H PFG‐NMR Diffusion Study on a Sequence‐Defined Macromolecule: Confirming Monodispersity

Guo

Wetzel

Solleder

et al. 2019

Macro Chemistry & Physics

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A monodisperse decamer bearing ten different side chains, obtained via the iterative Passerini three‐component reaction and subsequent deprotection, is investigated by 1H pulsed field gradient (PFG) NMR. Both the stimulated echo (PFG‐STE) and a fast spin‐echo pulse sequence (β‐PFG‐SE) are applied to explore the translational diffusion properties of the sequence‐defined decamer in solution at different concentrations with the aim of establishing an independent and new method to confirm its monodispersity. The signals decay according to the expectation of monodisperse molecules in solution with a high experimental accuracy, indeed verifying the monodispersity of these decamers. The diffusion coefficients can further be interpreted in terms of molecular weight. Both NMR methods result in comparable diffusion coefficients, while the β‐PFG‐SE reduces the experimental time by a factor of about 18.

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Diffusion in Polymer Solutions: Molecular Weight Distribution by PFG‐NMR and Relation to SEC

Cited by 52 publications

References 34 publications

Dynamics of Sodium Ions and Water in Swollen Superabsorbent Hydrogels as Studied by ²³Na‐ and ¹H‐NMR

Dynamics of Sodium Ions and Water in Swollen Superabsorbent Hydrogels as Studied by ²³Na‐ and ¹H‐NMR

Scaling exponent and dispersity of polymers in solution by diffusion NMR

¹H PFG‐NMR Diffusion Study on a Sequence‐Defined Macromolecule: Confirming Monodispersity

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Diffusion in Polymer Solutions: Molecular Weight Distribution by PFG‐NMR and Relation to SEC

Cited by 52 publications

References 34 publications

Dynamics of Sodium Ions and Water in Swollen Superabsorbent Hydrogels as Studied by 23Na‐ and 1H‐NMR

Dynamics of Sodium Ions and Water in Swollen Superabsorbent Hydrogels as Studied by 23Na‐ and 1H‐NMR

Scaling exponent and dispersity of polymers in solution by diffusion NMR

1H PFG‐NMR Diffusion Study on a Sequence‐Defined Macromolecule: Confirming Monodispersity

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Dynamics of Sodium Ions and Water in Swollen Superabsorbent Hydrogels as Studied by ²³Na‐ and ¹H‐NMR

Dynamics of Sodium Ions and Water in Swollen Superabsorbent Hydrogels as Studied by ²³Na‐ and ¹H‐NMR

¹H PFG‐NMR Diffusion Study on a Sequence‐Defined Macromolecule: Confirming Monodispersity