Determination of the Degree of Hydrogenation in Hydrogenated Nitrile-Butadiene Rubber (HNBR)

Abstract A number of analytical techniques are available for the measurement of the residual unsaturation in HNBR polymers. However, to insure that high-quality HNBR products are produced, it is necessary to use a standard procedure throughout the industry which is quick, accurate, and precise. The two infrared methods discussed in this paper show good agreement with one another, as shown by the respective mean values in Table V. Thus, in the absence of a totally independent and universally accepted standard procedure, this crosscheck between two separate and absolute measurements for the degree of hydrogenation is the best possible support for their precision (1H-NMR spectroscopy for IR method #1 and IR spectroscopy for IR method #2). The two iodometric methods each exhibit significantly poorer precision ( 10 to 100 times) than either of the infrared methods. This is not surprising, since these wet chemical techniques are not discriminatory to any type of unsaturation present in the HNBR nor are they inherently precise due to the large number of test variables. This lack of precision, and the fact that these wet chemical methods are time consuming, eliminates them from consideration as quality-oriented testing methods for measuring the degree of hydrogenation in HNBR. Both IR methods exhibit good reproducibility which greatly exceeds that of iodometry. The statistical analysis of these IR techniques does not present any significant differences between them. IR method #1 requires virtually no preparation time, since extraction of the HNBR rubber samples is not required. Furthermore, IR method #1 is less susceptible to impurities and subsequent user interpretation, since the hydrogenated butadiene peaks at 723 cm−1 are not required for the analysis. In conclusion, due to simplicity and speed of the analysis, IR method #1 is much more robust for use by the industry and their customers for the measurement of carbon-carbon double-bond unsaturation in HNBR.