Natural rubber FTIR spectra

NMR spectroscopy and Fourier transform infrared (FTIR) spectroscopy are the main techniques used to provide microstructure information that is especially important for differentiating Hevea rubber from other types of naturally occurring and synthetic poly-isoprene. Both proton ( FI) and carbon ( C) NMR spectroscopy are used to obtain spectra of natural rubber in solution, and are shown in Figure 1. In the NMR spectrum, the olefinic proton gives rise to a peak 5.0 ppm, the methylene protons 2.0 ppm, and the methyl protons 1.6 ppm. 

An FTIR spectrum of natural rubber is shown in Figure 2. A number of peaks corresponding to unique molecular vibrations around the carbon-carbon double bond are observed. The CH stretch from... 

When only spectroscopic methods are used, they are able to identify polymer components with respect to their chemical nature. However, in many cases, they are unable to answer the question whether two chemical structures are combined to yield a copolymer or a blend or both. For example, analyzing a rubber mixture one is able to identify styrene and butadiene as the monomer units. However, using FTIR or NMR it is impossible to decide if the sample is a mixture of polystyrene (PS) and polybutadiene (PB),or a copolymer of styrene and butadiene, or a blend of a styrene-butadiene copolymer and PB. For the latter case, even the copolymer composition cannot be determined just by running a FTIR or NMR spectrum. 

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