NMR Relaxation Studies of Elastomers

Asano, Atsushi

doi:10.1016/bs.arnmr.2015.04.001

Cited by 14 publications

(7 citation statements)

References 109 publications

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“…The Weibullian function was used to describe the decay associated to protons in the network chains fluctuating between constraints; the exponential function was used to reproduce the transverse magnetization decay of protons in less-constrained dangling chains and liquid-like sol components [59][60][61].…”

Section: Analysis Of the Dq Build-up Curvesmentioning

confidence: 99%

“…In this work, we used a phenomenological approach to the analysis of the CPMG decay curves, which were reproduced using a linear combination of a Weibullian function and an exponential function (Equation ( 3)) [59][60][61], characterized by the decay constants T 2,weib and T 2,exp , respectively. The Weibullian function represents the contribution of the network chains fluctuating between constraints responsible for the short time decay of transverse magnetization, while the long time decay, ascribable to dangling chains and sol components, is described by the exponential function.…”

Section: H Transverse Relaxation By Cpmg Experimentsmentioning

confidence: 99%

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Influence of Sulfur-Curing Conditions on the Dynamics and Crosslinking of Rubber Networks: A Time-Domain NMR Study

et al. 2022

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The characterization of the structural and dynamic properties of rubber networks is of fundamental importance in rubber science and technology to design materials with optimized mechanical properties. In this work, natural and isoprene rubber networks obtained by curing at three different temperatures (140, 150, and 170 °C) and three different sulfur contents (1, 2, and 3 phr) in the presence of a 3 phr accelerator were studied using a combination of low-field time-domain NMR (TD-NMR) techniques, including 1H multiple-quantum experiments for the measurement of residual dipolar couplings (Dres), the application of the Carr–Purcell–Meiboom–Gill pulse sequence for the measurement of the transverse magnetization decay and the extraction of 1H T2 relaxation times, and the use of field cycling NMR relaxometry for the determination of T1 relaxation times. The microscopic properties determined by TD-NMR experiments were discussed in comparison with the macroscopic properties obtained using equilibrium swelling, moving die rheometer, and calorimetric techniques. The obtained correlations between NMR observables, crosslink density values, maximum torque values, and glass transition temperatures provided insights into the effects of the vulcanization temperature and accelerator/sulfur ratio on the structure of the polymer networks, as well as on the effects of crosslinking on the segmental dynamics of elastomers. Dres and T2 were found to show linear correlations with the crosslink density determined by equilibrium swelling, while T1 depends on the local dynamics of polymer segments related to the glass transition, which is also affected by chemical modifications of the polymer chains occurring during vulcanization.

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Section: Analysis Of the Dq Build-up Curvesmentioning

confidence: 99%

Section: H Transverse Relaxation By Cpmg Experimentsmentioning

confidence: 99%

Influence of Sulfur-Curing Conditions on the Dynamics and Crosslinking of Rubber Networks: A Time-Domain NMR Study

et al. 2022

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“…In MAS experiments, possibilities of deformation 34 of soft materials like an elastomer due to high rotor frequencies must be considered. Additionally, softening due to higher temperature aids in deforming the sample.…”

Section: ■ Appendixmentioning

confidence: 99%

NMR Studies on the Phase-Resolved Evolution of Cross-Link Densities in Thermo-Oxidatively Aged Elastomer Blends

Karekar

Oßwald²,

Reincke³

et al. 2020

Macromolecules

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A knowledge of the distribution of cross-link densities (CDs) in the constituent rubber phases of an elastomer blend is essential to understand its overall service properties, but phase-resolved CD estimations have so far been limited to qualitative assessments. In a first study of its kind, we demonstrate a phase-resolved quantification of the CDs in sulfur-cured blends of natural rubber (NR) and styrene–butadiene rubber (SBR) using solid-state 1H homonuclear dipolar double-quantum (DQ) magic-angle spinning (MAS) NMR spectroscopy. The blends were also subjected to prolonged thermo-oxidative aging to monitor the chemical changes in the two phases. Analyses of the residual dipolar coupling constant (D res), arising due to spatial restrictions by cross-links to molecular motions, as observed in MAS and static 1H DQ experiments, suggest that unaged NR and SBR cross-link to similar extents. A minimum in D res after around 500 h of aging duration is observed in NR, associated with the formation of highly mobile defect fractions, as seen from free induction decay (FID) combined with transverse relaxometry, with further cross-linking up to 1000 h. SBR appears more stable, with a gradual increase in D res over the aging duration. Phase-resolved experiments reveal a somewhat less cross-linked SBR phase in an unaged 50:50 blend. The phase-specific distribution of CDs in the blend phases becomes significant upon aging, which suggests that NR ages more strongly in the blend as compared to the aged single vulcanisates, thus dictating the blend properties.

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“…Homonuclear and heteronuclear residual dipolar couplings (RDCs) or quadrupolar interactions in soft solids such as elastomers and biological tissues represent an important source of information about the structure and molecular dynamics [1][2][3][4][5]. Proton residual dipolar couplings in elastomers reflect changes in the cross-link density, temperature, the uniaxial and biaxial extension or compression as well as the presence of fillers and penetrant molecules.…”

Section: Introductionmentioning

confidence: 99%

“…Proton residual dipolar couplings in elastomers reflect changes in the cross-link density, temperature, the uniaxial and biaxial extension or compression as well as the presence of fillers and penetrant molecules. Structure-dynamics-function relationships using RDCs can be investigated for the broad class of elastomer materials [2][3][4].…”

Section: Introductionmentioning

confidence: 99%

Bimodal 1H Double Quantum Build-Up Curves by Fourier and Laplace-like Transforms on Aged Cross-Linked Natural Rubber

Moldovan

Fechete

2021

Polymers

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The 1H DQ Fourier and Laplace-like spectra for a series of cross-linked natural rubber (NR) samples naturally aged during six years are presented and characterized. The DQ build-up curves of these samples present two peaks which cannot be described by classical functions. The DQ Fourier spectra can be obtained after a numeric procedure which introduces a correction time which depends less on the chosen approximation, spin-½ and isolated CH2 and CH3 functional groups. The DQ Fourier spectra are well described by the distributions of the residual dipolar coupling correlated with the distribution of the end-to-end vector of the polymer network, and with the second and fourth van Vleck moments. The deconvolution of DQ Fourier spectra with a sum of four Gaussian variates show that the center and the width of Gaussian functions increase linearly with the increase in the cross-link density. The Laplace-like spectra for the natural aged NR DQ build-up curves are presented. The centers of four Gaussian distributions obtained via both methods are consistent. The differences between the Fourier and Laplace-like spectra consist mainly of the spectral resolution in the favor of Laplace-like spectra. The last one was used to discuss the effect of natural aging for cross-linked NR.

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NMR Relaxation Studies of Elastomers

Cited by 14 publications

References 109 publications

Influence of Sulfur-Curing Conditions on the Dynamics and Crosslinking of Rubber Networks: A Time-Domain NMR Study

Influence of Sulfur-Curing Conditions on the Dynamics and Crosslinking of Rubber Networks: A Time-Domain NMR Study

NMR Studies on the Phase-Resolved Evolution of Cross-Link Densities in Thermo-Oxidatively Aged Elastomer Blends

Bimodal 1H Double Quantum Build-Up Curves by Fourier and Laplace-like Transforms on Aged Cross-Linked Natural Rubber

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