High-Resolution Latex-State 13C-NMR Spectroscopy for Natural Rubber Vulcanizates

Kawahara, Seiichi; Ukawa, Jinta; Sakai, Junichiro; Yamamoto, Yasuhiko; Isono, Yoshinobu

doi:10.5254/1.3539414

Cited by 10 publications

(13 citation statements)

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“…Figure 6 shows plausible cross-linking junctions of cross-linked natural rubber. The present and previous works 7,[20][21] demonstrate that the tertiary and quaternary carbons linked to sulfur may be neighbors to carbon-carbon double bonds in trans form. As shown in Figure 6, the quaternary carbon linked to sulfur at a cross-linking junction may maintain the accordion structure of natural rubber, which is a main factor in the rubber elasticity.…”

Section: Resultssupporting

confidence: 65%

Mechanical properties and cross-linking structure of cross-linked natural rubber

Chaikumpollert

Yamamoto

Suchiva

et al. 2012

Polym J

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Molecular singularity of cross-linked natural rubber was proposed to be a significant cross-linking junction of rubber, on the basis of the assignment of nuclear magnetic resonance (NMR) signals achieved in our previous work. This molecular singularity was observed to have an important role in the most outstanding mechanical properties of the rubber, through the investigation of the relationships between the structure of cross-linking junctions and the mechanical properties of various cross-linked rubbers. The various cross-linked natural rubbers were prepared by conventional vulcanization (CV), efficient vulcanization (EV) and semi-EV (SemiEV) to have nearly identical cross-link densities. These rubbers were analyzed using solid-state NMR spectroscopy. Using 1 H-NMR spectroscopy, the amount of tertiary carbons linking to sulfur in the CV rubber was observed to be the same as those of the EV and SemiEV rubbers. 13 C-NMR spectroscopy revealed that the number of quaternary carbons linking to sulfur in the CV rubber was the largest among the rubbers. The CV rubber exhibited the best mechanical properties; hence, a cross-linking junction of quaternary carbons linked to sulfur was assigned to the molecular singularity.

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Section: Resultssupporting

confidence: 65%

Mechanical properties and cross-linking structure of cross-linked natural rubber

Chaikumpollert

Yamamoto

Suchiva

et al. 2012

Polym J

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“…The active molecular motion of the rubbers at 50°C was found to be important for the quantitative analysis of the epoxy group content for EDPNR‐1, EDPNR‐2, EDPNR‐3, and EDPNR‐4, whose glass transition temperatures ( T g ) were about −58.6°C, −51.5°C, −46.7°C, and −43.3°C, respectively. This is consistent with the previous result that the high resolution is achieved at T ‐ T g >70 K for the latex‐state NMR spectroscopy …”

Section: Resultssupporting

confidence: 93%

Latex-state NMR spectroscopy for quantitative analysis of epoxidized deproteinized natural rubber

Sae-heng

Kanya

Choothong

et al. 2017

Polym. Adv. Technol.

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Method of quantitative analysis through latex-state 13 C NMR spectroscopy was established for in situ determination of epoxy group content of epoxidized natural rubber in latex stage. The epoxidized natural rubber latex was prepared by epoxidation of deproteinized natural rubber with freshly prepared peracetic acid in latex stage. The resulting epoxidized deproteinized natural rubber (EDPNR) latex was characterized through latex-state 13 C NMR spectroscopy. Chemical shift values of signals of latex-state 13 C NMR spectrum for EDPNR were similar to those of solution-state 13 C NMR spectrum for EDPNR. Resolution of latex-state 13 C NMR spectrum was gradually improved as temperature for the nuclear magnetic resonance (NMR) measurement increased to 70°C. Signal-to-noise ratio of latex-state 13 C NMR measurement was similar to that of solution-state 13 C NMR measurement at temperature above 50°C. The epoxy group content determined through latex-state NMR spectroscopy was proved to be the same as that determined through solution-state NMR spectroscopy.

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“…Many trans-type species were generated in the sample prepared under general NR vulcanization conditions. The methine carbon signals of vulcanized junction points at 53.0–54.4 and 49.0–50.1 ppm in Figure d and in the DEPT135 spectrum (Figure e) were attributed to the reported crosslinked structures A and D, − ,,,− although our assignments for both A and D were inconsistent with those of the previous NMR studies (see Table S5). Detailed assignments in the 48–60 ppm region are displayed in Figure .…”

Section: Resultscontrasting

confidence: 82%

“…These studies reported the presence of carbon signals of possible crosslinking points in structures A−C, H, and I 47 (Figure 2a) and predicted the crosslinked structures D−F. 42,43 However, many questions remain. First, unlike commercial NR products, the samples used in the above studies were prepared without the kneading or heat pressing stages commonly used for preparing NR products (see Figure 1a).…”

Section: ■ Introductionmentioning

confidence: 99%

High-Field Nuclear Magnetic Resonance Studies Reveal New Structural Landscape of Sulfur-Vulcanized Natural Rubber

et al. 2022

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Despite intensive research efforts over the past 3 decades, the structural analysis of sulfur-vulcanized natural rubber (NR) remains challenging owing to the complexity and low population of its sulfur moieties. Herein, solid vulcanized NR samples and NR samples reacted with sulfur and other reactants in an organic solvent were analyzed by solid-state NMR with fast magic-angle spinning and solution NMR, respectively. The present high-field two-dimensional NMR analysis revealed six novel sulfur moieties in these samples, including cyclic sulfides, cyclic di/polysulfides, and crosslinked structures with a vinylidene group. While previous studies reported a variety of sulfur-crosslinked structures in NR, our analysis identified only two dominant types of crosslinked structures that matched those reported previously. Our NMR assignments for the crosslinked structures were inconsistent to a large extent with those presented in the previous studies; thus, in the current work, the crosslinked structures were reassigned using the new data. Based on quantitative NMR analysis, this study also provides the first tangible evidence that cyclic rather than crosslinked sulfides can be the dominant sulfur moieties in vulcanized NR. These results may drastically alter the previously established structural landscape of sulfur-vulcanized NR.

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High-Resolution Latex-State 13C-NMR Spectroscopy for Natural Rubber Vulcanizates

Cited by 10 publications

References 0 publications

Mechanical properties and cross-linking structure of cross-linked natural rubber

Mechanical properties and cross-linking structure of cross-linked natural rubber

Latex-state NMR spectroscopy for quantitative analysis of epoxidized deproteinized natural rubber

High-Field Nuclear Magnetic Resonance Studies Reveal New Structural Landscape of Sulfur-Vulcanized Natural Rubber

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