Chapter 8: Rubber-state NMR Spectroscopy

Vulcanized rubbers, i.e., vulcanized natural rubber and vulcanized chloroprene rubber, were characterized by rubber-state NMR spectroscopy. High resolution ¹H and ¹³C-NMR spectra were accomplished for the vulcanized rubbers due to fast magic angle spinning. The correlation between ¹H and ¹³C of the vulcanized rubbers was investigated by one- and two-dimensional measurements. As for vulcanized natural rubber, the signals, appearing between 40 and 60 ppm, were well assigned by rubber-state NMR spectroscopy; for instance, the signal at 40 ppm was assigned to C1 of trans-1,4-isoprene units, while the signal at 44 ppm was assigned to secondary carbons linking to an S atom and signals at 58 ppm were assigned to tertiary and quaternary carbons linking to S atoms. In contrast, for chloroprene rubber, a ¹H-signal at 0.9 ppm, appearing after vulcanization, was correlated to a ¹³C-signal at 14.5 ppm and the ¹H signal at 1.3 ppm was correlated to a ¹³C-signal at 22.5, 29.5, and 31.8 ppm. A constitutional unit, i.e., CH₃–CH₂–CH₂–S–R was found for vulcanized chloroprene rubber by rubber-state NMR spectroscopy.