The infrared spectra and structures of polyisoprenes

Evidence is offered which confirms, and in some cases, changes previously suggested assignments of bands in the spectra of Hevea and balata. In particular it is shown that bands at 764 (13.1 μ) and 742 cm.−1 (13.5 μ) are probably connected with vibrations of the cis‐ or trans‐C (CH3)CH group, a band at 11.30 cm.−1 (8.85 μ) is due to a CCH3 vibration of the cis‐C(CH3)CH group, a band at 1155 cm.−1 (8.68 μ) is due to the CCH3 vibration of the trans‐C(CH3)CH group. Likewise the bands at 1315 (7.60 μ) and 1325 cm.−1 (7.55 μ) are probably due to a CH vibration of the cis‐ and trans‐C(CH3)CH groups, respectively. The 1130‐cm.−1 band and the 1155‐cm.−1 band are found in spectra of polydimethylbutadiene and thus are probably group frequencies. The 1315 and 1325‐cm.−1 bands (shifted) are also found in polybutadiene and polypiperylene spectra and thus are probably group frequencies also. It is also shown that the 890‐, 1645‐, and 3077‐cm.−1 bands are best explained by the presence of an isopropenyl, CH2C(CH3) group. These assignments are based on a study of the polarization spectra, the spectra of maleic anhydride adducts and hydrogenated polyisoprenes, and on microstructure determinations.