Take mercaptan as raw material
Mercaptans are one of the main raw materials for the synthesis of vulcanizing agents. Mercaptans can react with oxygen under the action of hydroxides of alkali metals and alkaline earth metals to obtain vulcanizing agents. It can also be mixed with elemental sulfur as a raw material to synthesize an organic vulcanizing agent under the action of a basic catalyst.
The earliest catalysts used in this synthesis route are amines, alkanolamines, thiolates, alcoholates, and inorganic bases. However, the use of these catalysts has disadvantages such as low yield, low product purity, and unpleasant odor. Therefore, the research of new catalysts is the focus of this synthetic route. Substituting alkylene oxide for the olefin oxide group in the composition further improves the yield of polysulfides, the chroma becomes lower and the chroma is less than or equal to, and the product has no unpleasant odor or turbidity. Some scholars began to use resin as a catalyst. It is proposed to use organic anion exchange resins containing quaternary ammonium hydroxide groups or tertiary amine groups as catalysts. This resin exists in the reaction system in the form of beads or bidentate, has low solubility and is easy to recycle, but the organic vulcanizing agent The yield is not high.
In order to solve this problem, a study was carried out, and a resin with one or one form was proposed as a catalyst. This resin has a highly cross-linked macroporous structure. Compared with gel-type resins, it has greater catalytic activity during the reaction and can effectively increase the yield of organic vulcanizing agents. Aretz proposed the use of polystyrene-divinylbenzene-resin containing muscle groups and mitochondria as a catalyst. This resin can react low-level organic disulfides and polysulfides with elemental sulfur to obtain high-level polysulfides.
In addition, the resin can also react high-level organic vulcanizing agents with mercaptans to obtain lower-level polysulfides. The resin exists in the reaction liquid in the form of pellets or beads, and is easily separated after the reaction is completed. Fremi has developed a polystyrene-divinylbenzene-based resin grouped with ethylenediamine or polyvinylpolyamine. This catalyst can effectively increase the conversion rate of the reactants.
The application of these new catalysts not only effectively increases the sulfur content of the vulcanizing agent, but also broadens the range of raw materials. More importantly, it overcomes the shortcomings of traditional catalysts such as low yield, low product purity, and unpleasant smell. However, the synthesis of the new catalyst is complicated, the raw material cost is too high, and some raw materials are not easy to obtain and not easy for industrial application.