NMR Reveals Non‐Distributed and Uniform Character of Network Chain Dynamics

Saalwächter, Kay; Sommer, Jens‐Uwe

doi:10.1002/marc.200700169

Cited by 48 publications

(84 citation statements)

References 52 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…(4) to attain reasonable fitting of the build-up curves is in accord with previous observations on swollen networks [85]. While distributions due to variations in the chain length between crosslinks as well as the distribution expected on the basis of a Gaussian distribution of end-to-end distances are screened by the cooperativity of the chain motions (''packing'') in unswollen elastomers, such effects, as well as topologically induced swelling heterogeneities, reappear in swollen networks [76,85,86].…”

Section: Analysis Of the Network Fractionsupporting

confidence: 84%

Hydrogel formation by photocrosslinking of dimethylmaleimide functionalized polyacrylamide

Seiffert

Oppermann

Saalwächter

2007

Polymer

Self Cite

100

View full text Add to dashboard Cite

Section: Analysis Of the Network Fractionsupporting

confidence: 84%

Hydrogel formation by photocrosslinking of dimethylmaleimide functionalized polyacrylamide

Seiffert

Oppermann

Saalwächter

2007

Polymer

Self Cite

100

View full text Add to dashboard Cite

“…20 However, the most recent and quantitative approach for the measurement of weak residual dipolar coupling is the double- quantum (DQ) or, more generally, multiple-quantum (MQ) NMR technique. [21][22][23][87][88][89][90] The essential advantage of MQ spectroscopy is that, in the same experiment, two qualitatively different sets of data, a buildup curve (I DQ ) dominated by spin-pair double-quantum (DQ) coherences and a decay curve (I ref ), are measured. They can be used to independently analyze residual couplings and the chain dynamics.…”

Section: Methodsmentioning

confidence: 99%

Uncertainties in the Determination of Cross-Link Density by Equilibrium Swelling Experiments in Natural Rubber

et al. 2008

View full text Add to dashboard Cite

Equilibrium swelling is a feasible and simple experiment to determine the cross-link density of networks. It is the most popular and useful approach; however, in most of the cases, the given values are highly uncertain if not erroneous. The description of the complex thermodynamics of swollen polymer networks is usually based on the Flory-Rehner model. However, experimental evidence has shown that both the mixing term described by the Flory-Huggins expression and the elastic component derived from the affine model are only approximations that fail in the description and prediction of the rubber network behavior. This means that the Flory-Rehner treatment can only give a qualitative evaluation of cross-link density because of its strong dependence on the thermodynamic model. In this work, the uncertainties in the determination of the cross-link density in rubber materials by swelling experiments based on this model are reviewed. The implications and the validity of some of the used approximations as well as their influence in the relationship of the cross-link densities derived from swelling experiments are discussed. Importantly, swelling results are compared with results of a completely independent determination of the cross-link density by proton multiple-quantum NMR, and the correlation observed between the two methods can help to validate the thermodynamic model.

show abstract

“…(56) Therefore, the normalized DQ build-up curve of a bulk rubber can be analyzed in the quasi-static limit in terms of a single D res (38)…”

Section: Methodsmentioning

confidence: 99%

Structure of Poly(vinyl alcohol) Cryo-Hydrogels as Studied by Proton Low-Field NMR Spectroscopy

et al. 2008

View full text Add to dashboard Cite

The network structure of poly(vinyl alcohol) (PVA) hydrogels obtained by freezing−thawing cycles was investigated by solid-state 1H low-field NMR spectroscopy. By the application of multiple-quantum NMR experiments, we obtain information about the segmental order parameter, which is directly related to the restrictions on chain motion (cross-links) formed upon gelation. These measurements indicate that the network mesh size as well as the relative amount of nonelastic defects (i.e., non-cross-linked chains, dangling chains, loops) decrease with the number of freezing−thawing cycles but are independent of the polymer concentration. The formation of the PVA network is accompanied by an increasing fraction of polymer with fast magnetization decay (∼20 μs). The quantitative study of this rigid phase with a specific refocusing pulse sequence shows that it is composed of a primary crystalline polymer phase (∼5%), which constitutes the main support of the network structure and determines the mesh size, and a secondary population of more imperfect crystallites, which increase the number of elastic chain segments in the polymer gel but do not affect the average network mesh size appreciably. Correspondingly, progressive melting of the secondary crystallites with increasing temperature does not affect the network mesh size but only the amount of network defects, and melting of the main PVA crystallites at ∼80 °C leads to the destruction of the network gel and the formation of an isotropic PVA solution.

show abstract

NMR Reveals Non‐Distributed and Uniform Character of Network Chain Dynamics

Cited by 48 publications

References 52 publications

Hydrogel formation by photocrosslinking of dimethylmaleimide functionalized polyacrylamide

Hydrogel formation by photocrosslinking of dimethylmaleimide functionalized polyacrylamide

Uncertainties in the Determination of Cross-Link Density by Equilibrium Swelling Experiments in Natural Rubber

Structure of Poly(vinyl alcohol) Cryo-Hydrogels as Studied by Proton Low-Field NMR Spectroscopy

Contact Info

Product

Resources

About