Structural characterization of vulcanized natural rubber by latex state ¹³C NMR spectroscopy

Abstract

Structural characterization of vulcanized natural rubber was performed by high‐resolution latex‐state 13C NMR spectroscopy. The vulcanized natural rubber latex was prepared by vulcanization of high ammonia natural rubber latex with sulfur and sodium di‐n‐butyldithiocarbamate as vulcanizing agents. High resolution was attained for latex‐state 13C NMR spectroscopy even after vulcanization of the rubber latex, as is evident from no background in spectrum and narrow half width of signals, which were independent of vulcanization time. Small signals at 44 and 58 ppm in the carbon region were assigned by measurements of both distortionless enhancement by polarization transfer (DEPT) and attached proton test (APT) to secondary, tertiary, and quaternary carbons of crosslinking points. The assignment was proved by high‐resolution solution‐state NMR spectroscopy of vulcanized liquid cis‐1,4‐polyisoprene as a model, in which DEPT, APT, 2‐dimensional 1H‐13C correlation (HETCOR), and 2‐dimensional heteronuclear multiple bond correlation (HMBC) measurements were applied. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1003–1009, 2007

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

“…Structure E was observed in the solution-reacted NR sample but not in the solid vulcanized sample. Structure F was part of structure ε, and its presence was predicted but not identified experimentally in previous studies. , As discussed above, the crosslinked structure ε containing a vinylidene group was identified in this work for the first time. Furthermore, the presence of cyclic structure G could not be confirmed using our data.…”

“…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).…”

“…55−58 As a result, several new vulcanized structures were identified, namely, cyclic sulfides, cyclic di/polysulfides, episulfides, and another crosslinked structure bearing a vinylidene group (Figure 2b) that was only speculated in previous studies. 42,43 Furthermore, quantitative NMR analysis allowed us to identify an unexpectedly high fraction of novel cyclic mono/di/ polysulfide structures, comparable to that of crosslinked structures. Only two main types of crosslinked structures (A and D in Figure 2a) were identified from our NMR data among several sulfur-crosslinked structures reported or predicted in previous studies (see Figure 2a), besides the newly identified crosslinked structure ε (Figure 2b).…”

Sulfur-Free Prevulcanization of Natural Rubber Latex by Ultraviolet Irradiation

“…Therefore, the UV-irradiated PVNRL and the NR latex were only characterized using 13 C nuclear magnetic resonance spectroscopy (Bruker Biospin 500 13 C NMR operating at 500 MHz). The samples for 13 C NMR were prepared and measured at 25 °C …”

Structural Analysis of Crosslinking Junctions of Vulcanized Natural Rubber by Field Gradient Fast Magic Angle Spinning Solid-State Nmr Spectroscopy

“…As these do not appear in the solution 13 C-NMR spectrum of uncured natural rubber, they must be derived from crosslinks. Past studies yielded single broad signals at 40, 44, 50 and 58 ppm, respectively, each of which was treated as a single signal for assignment and analysis [12,13,[22][23][24][25][26][34][35][36][37][38]. However, using an FG-MAS probe, fast MAS and NMR locking, it was shown that a plurality of sharp signals existed at 40, 44, 50 and 58 ppm, broad signals disappearing completely from the spectrum.…”