Raman Spectrographic Studies of the Vulcanization of Rubbers. I. Raman Spectra of Vulcanized Rubbers

Abstract

Abstract We have demonstrated that good quality Raman spectra can be obtained from vulcanizates prepared from cis-l,4-polybutadiene. Furthermore, significant differences are seen in the spectra of extracted vulcanizates prepared from various recipes. Tentative assignments have been made for many of the following Raman lines observed in the spectra. 1. The 1633, 1187, 734, and 720 cm−1 lines are thought to be associated with dialkenyl sulfide crosslinks. 2. Lines occurring at 440 and 505 cm−1 are assigned to polysulfidic and disulfidic structures respectively. 3. The 635, 690, and 708 cm−1 lines are thought to be associated with cyclic sulfides. In particular, the 635 cm−1 line with six membered thioalkenes, the 690 cm−1 line with five membered thioalkanes and the 708 cm−1 line with five membered thioalkenes. 4. Pendent side groups derived from TMTD are thought to have lines occurring at 1142 and 577 cm−1. Other lines occurring in the Raman spectra of the vulcanizates examined cannot be assigned with the same degree of confidence. The line occurring at 1606 cm−1 may be associated with conjugation but further work is necessary to verify it. The recipes chosen do not necessarily reflect those used currently in industry but were designed to accentuate certain structural features in the network. Consequently, the weak band at 1587 cm−1, observed only in systems with large amounts of TMTD and associated with vinyl thioether type structures, should not be overemphasized. Lines occurring at 558, 852, and 872 cm−1 are unassigned at present. Although the initial results are encouraging, it must be stated that many problems exist. Due to difficulties associated with fluorescence and degradation, Raman spectra of many important rubber systems will be difficult to obtain. Low levels of fluorescence cause serious problems when weak lines are present and when quantitative measurements of line intensities are made.