Some polyisoprene samples of different microstructure contents were studied by Fourier transform infrared (FTIR) and 1H Nuclear magnetic resonance (1H NMR). On the basis of detailed analysis of FTIR spectra of polyisoprene, the shift of absorption peaks caused by microstructure content’s variation was discussed. The contents of the polyisoprene samples’ microstructure which was determined by the 1H NMR was used as the standard. Through the choice, calculation, and comparison with the corresponding absorption peaks of FTIR, a method based on the results of the analysis has been developed for the determination of the microstructure contents of polyisoprene by FTIR. 1. Introduction As it is well known, polyisoprene (PIp) is one kind of important rubbers, and there are four kinds of microstructure in its molecular chain which are cis-1,4-, trans-1,4-, 1,2-, and 3,4-polyisoprene. The main ingredient of nature rubber is cis-1,4- or trans-1,4-polyisoprene. For example, Hevea brasiliensis (the Brazilian rubber tree) is polyisoprene with more than 5,000 cis-1,4-repeat units except for the transinitiator residue of repeat units ranging from 1 to 4, depending on the plant species. Gutta-percha, Balata, or Malaysian rubber is polyisoprene with trans-1,4-repeat units [1–4]. Since English chemist Michael Faraday found that the structure unit of nature rubber was C5H8, the research of synthetic polyisoprene keeps active [1–7]. Except for the synthesis of high content of cis-1,4- or trans-1,4-polyisoprene to imitate and replace nature rubber, the research on synthesis of polyisoprene with variable microstructure contents keeps attractive in order to obtain some materials of special properties. For example, with 3,4- unit content’s increasing, the curing rate and low temperature properties of polyisoprene decrease, but hardness and elasticity increase, as well as tensile properties, tension set, and tearing strength maintain are slightly changed. Particularly, the water resistance and hermeticity of polyisoprene with high 3,4-unit content can compare with butyl rubber [8–11]. The application of polyisoprene with high 3,4-unit content in tread can improve the skidding resistance, traction property, and cutting growing resistance and also can decrease the generation of heat by friction So it is the new varieties of rubber for a fuel-saving, environmental protection and safety tire. Most of the studies on microstructure of polymers are characterized by nuclear magnetic resonance (NMR) spectrophotometer and FTIR [12, 13]. The first extensive IR spectroscopic studies of
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