Comparison of residual dipolar interactions in uncross-linked and cross-linked natural rubber by high-resolution solid-state NMR spectroscopy

Probing Rubber Cross-Linking Generation of Industrial Polymer Networks at Nanometer Scale

“…It has been shown that local residual dipolar broadening of protons coupled to 13 C was a sensitive way, through cross-polarization under magic angle spinning, for observing motional constraints from networks and entanglements in cross-linked and un-cross-linked rubber systems. 9 Other attempts by 13 C high resolution magic angle spinning solid state NMR spectroscopy have been used for determining the cross-link density of blended samples. 10 Information about heteronuclear dipolar coupling (residual heteronuclear dipolar coupling in polymers) and implicitly about cross-link density of blended samples can be determined by applying the consecrated recoupling techniques like "spin-echo", "spin- echo double resonance (SEDOR)", and "rotational-echo double resonance (REDOR)".…”

“…However, the structural information obtained by these standard NMR techniques remain highly model dependent. It has been shown that local residual dipolar broadening of protons coupled to 13 C was a sensitive way, through cross-polarization under magic angle spinning, for observing motional constraints from networks and entanglements in cross-linked and un-cross-linked rubber systems . Other attempts by 13 C high resolution magic angle spinning solid state NMR spectroscopy have been used for determining the cross-link density of blended samples .…”

Toward recording 33S NMR spectra of cross‐linked elastomers: Relaxation dynamics perspective

“…Chemical characterization of cross‐link junctions in sulfur‐vulcanized elastomers is difficult because of the small amount of cross‐links points present in these materials. For the same reason, the use of 13 C NMR to observe new chemical structure upon sulfur vulcanization suffers from low sensitivity and so far mainly the indirect observation of various cross‐link densities through difference in molecular mobility has been reported by solid‐state NMR measurements . The mechanical properties of sulfur vulcanizates depend not only on the cross‐link density, but also to a large extent on the distribution of sulfur bridges of various ranks (monosulfidic and polysulfidic) which in turn are controlled by vulcanization conditions such as sulfur/accelerator ratio, curing time, and temperature .…”

“…For the same reason, the use of 13 C NMR to observe new chemical structure upon sulfur vulcanization suffers from low sensitivity 1,2 and so far mainly the indirect observation of various cross-link densities through difference in molecular mobility has been reported by solid-state NMR measurements. [3][4][5][6][7] The mechanical properties of sulfur vulcanizates depend not only on the cross-link density, but also to a large extent on the distribution of sulfur bridges of various ranks (monosulfidic and polysulfidic) which in turn are controlled by vulcanization conditions such as sulfur/accelerator ratio, curing time, and temperature. 8 Consequently, the direct detection of NMR spectra of 33 S-labeled cross-linked elastomers could provide invaluable information on the chemical structure of cross-link junctions and their inherent dynamics.…”

Measurement of 13C–1H dipolar couplings in solids by using ultra-fast magic-angle spinning NMR spectroscopy with symmetry-based sequences

“…Furthermore, the high gyromagnetic ratio of 1 H nuclei leads to large dipolar couplings, which allow determining inter-nuclear distances up to 6 A ånd dihedral angles or order parameters with a high accuracy. 1 In practice, 13 C-1 H dipolar couplings were used to obtain information about the dynamics and the molecular order of polymers and mesophases, [2][3][4][5][6][7] as well as to measure distances and dihedral angles in peptides and proteins. 1,[8][9][10] In particular, 13 C-1 H dipolar coupling can aid to localize the position of hydroxyl protons in hydrogen bonds, which are difficult to observe by X-ray diffraction.…”