The mechanism of the reaction of diethyl disulfide with natural rubber has been reported in detail in the literature. However, due to the shortcomings of traditional methods, people are constantly exploring new research methods. Since the 1980s, the model compound (MCV) method (the model compound means that the molecular structure is similar to the real rubber molecule, but the size is small. ), with the help of HPLC (high performance liquid chromatograph) to observe the cross-linked precursor and speculate the subsequent formation of the sulfur crosslinking model. However, since the MCV's various hardening reactions occur at the same time, it is difficult to observe the response pathways that individual components follow.
In order to overcome this problem, in the mid 1990s, the Nieuwenhuizen research team of Leiden University developed a new method to study the low relative molecular weight model compounds and their precursors of sulfur-containing cross-linking under the condition of simulated vulcanization, so as to understand the chemical pathways of change and the catalysis of complexes. By using this method, combined with quantum chemical calculations, they revealed a large number of homogeneous catalytic reactions during vulcanization, including precursor formation, desulfurization, degradation and sulfur crosslinking, of the zinc disulfide (ZDMC) and thiol-thiazole zinc salts (ZMBT). The uniqueness of the study is: (1) using quantum chemical calculation and matrix-assisted laser desorption ionization mass spectrometer, the first theoretically and experimentally confirmed the existence of the intermediate of zinc disulfide complexes. For a long time, it has been believed that sulfur-rich zinc promoter complexes in the vulcanization process play a central role in the vulcanization process, that is, to activate ground state sulphur, to facilitate the exchange and transfer of S atoms during rubber vulcanization, and to influence the formation of S-crosslink bond. However, the rich S-amino acid zinc disulfide complexes are active and can quickly release the connected S to an appropriate s-receptive body, so the usual spectral technique does not detect its existence. A matrix-assisted laser desorption ionization mass spectrometer was used to treat the isolated complexes in a vacuum environment (preventing s atom conversion or loss), and the results detected that the complex could be enriched to four s atoms. (2) The rubber vulcanization mechanism of zinc disulfide and thiazole zinc salts was revealed by using model compounds under simulated vulcanization conditions.