Infrared study of out-of-plane deformation vibrations of linear and cyclized 1,2- and 3,4-polyisoprenes

This study concerns the influence of 3,4 and 1,2 addition in cyclic polyisoprenes on the extinction coefficients of the absorption bands at 890 and 910 cm^?1 due to out-of-plane vibrations of ?CH₂ of the isopropenyl and vinyl groups (correspoding, respectively, to 3,4 or 1,2 addition). In contrast to analogous bands characteristic of 1,4 addition (especially in the case of cis-1,4 units of polybutadiene), the shape, position, and intensity of these bands are not influenced by changes in the structure of the macromolecular chain. The extinction coefficients of both bands did not change substantially, although the overall presence of both linear and cyclic forms varied over a wide range. It can be assumed, therefore, that the influence of configurational changes upon the intensity of the absorption bands of out-of-plane vibrations for double bonds is not a general phenomenon.