The key of research and production of silicone rubber in China – dimethyldiethoxysilane

Basic hot vulcanized silicone rubber

China began to research and manufacture the raw rubber of heat vulcanized (also known as heat cured) silicone rubber in the late 1950s. It is not too late in the world that China began to explore silicone rubber. Due to the development work needs a large number of high-purity hydrolysates of dimethyldichlorosilane (from which octamethylcyclotetrasiloxane (D4, or DMC) is obtained; previously, due to the lack of a large number of methylchlorosilane, it is difficult to get a large number of pure dimethyldichlorosilane, and there is not enough to trial produce the basic raw material of raw silicone rubber octamethylcyclotetrasiloxane. There is also a need for appropriate catalysts in ring opening polymerization, which are major problems in the early stage of development. In particular, the industrial production of methylchlorosilane is very difficult, so the technical personnel of relevant units in China have paid a lot of labor and spent a lot of time.

Yang Dahai, Shenyang Chemical Research Institute, etc. presented the samples of silicone rubber prepared from the self-made dimethyldichlorosilane to the 10th anniversary of the national day. Lin Yi and Jiang Yingyan, researchers of the Institute of chemistry, Chinese Academy of Sciences, also carried out the development of methyl silicone rubber very early. In the 1960s, more units developed silicone rubber.

Only after the success of the direct synthesis of methylchlorosilane in the stirred bed, can the raw materials for the synthesis of raw silicone rubber be obtained. Because the demand of silicone rubber is very urgent, so there are units in Shanghai and North China to start to develop silicone rubber. For example, Shanghai Chemical Research Institute in Shanghai studies the synthesis of methyl chlorosilane monomer and the exploration and test of silicone rubber; Shanghai Xincheng chemical plant and Shanghai resin plant consider the synthesis of silicone rubber from the perspective of production.

In the north, the Research Institute of Jihua company, a chemical industry base in China, is mainly engaged in the research and development of synthetic rubber. Later, the research institute increased research and development of silicone rubber led by Zhu BAOYING. There are also design institutes and production plants in Jihua company, which have a good one-stop cooperation condition to develop a complete set of process from methyl chlorosilane monomer to synthetic silicone rubber.

In 1958, the organosilicon part of Shenyang Chemical Research Institute was moved to the newly established Beijing Chemical Research Institute. In the early 1960s, Shenyang Chemical Research Institute established a organosilicon Research Office headed by Zhang Erci and ye Qingxuan to develop organosilicon monomer and silicone rubber. According to the opinions of the Second Bureau of the Ministry of chemical industry, Shenyang Chemical Research Institute participated in the development of silicone rubber in the Research Institute of Jilin chemical company. Because the synthesis of silicone rubber also needs vinyl ring, so Shenyang Chemical Research Institute for the synthesis of methylhydrodichlorosilane and other supporting organosilicon monomers.

The first batch production of silicone rubber in Shanghai is "circuitous tactics"

In 1960, the plastic company of Shanghai Chemical Industry Bureau assigned Xincheng chemical plant a task to develop silicon rubber urgently needed by the military industry. Because the plant has chloromethane, a pesticide by-product of organosilicon raw material, it has the conditions to synthesize methyl chlorosilane, a raw material of silicon rubber. Xincheng chemical plant is a small public-private joint venture plant, with only two engineering technicians, Zheng Shanzhong and Xu Mingshan. They identified two key technical issues in the silicone rubber research project, one is the purification of dimethyldichlorosilane, the other is the study of polymerization process and the selection of catalyst. At that time, organosilicon monomers and intermediates were banned and blocked in China. At that time, the content of dimethyldichlorosilane in the synthesis of methylchlorosilane monomer in domestic stirred bed was low, and the efficient distillation technology had not been implemented yet, so it was impossible to obtain a large number of high-purity dimethyldichlorosilane monomer as the raw material of silicone rubber. Therefore, they can only use the dimethyldichlorosilane with low purity which can be obtained at that time to prepare ethoxyl derivatives by alcoholysis. The distance between the boiling point of methyltriethoxysilane (151 ° C) and the boiling point of dimethyldiethoxysilane (111 ° C) after alcoholization is relatively large, and the boiling point difference is as much as 40 ° C, which is easy to separate, so the dimethyldiethoxysilane with high purity can be obtained. Then, dimethyldiethoxysilane was hydrolyzed to octamethylcyclotetrasiloxane (methyld4). After fractionation, high purity D4 was produced, which solved the problem of raw material of silicone rubber. They call the method of obtaining D4 through indirect means of alcoholysis "circuitous tactics".

In the early stage of research and development of silicone rubber in China, there was a lack of understanding of the synthesis process of silicone rubber in western countries. Some units had tried relatively primitive ring opening catalysts such as sulfuric acid, ferric chloride, aluminum sulfate, etc. Then, the residual catalyst contained in hundreds of thousands of molecular weight raw silica gel is washed with distilled water on the double roller, so it is a very undesirable process to use this open-loop catalyst.

Zheng Shanzhong and Xu Mingshan, the two temporary catalysts who understand the unique properties, think that it has its rationality and advanced nature. It can not only improve the quality of silicone rubber, but also greatly simplify the post-processing work. At that time, foreign countries had not yet been used for industrial production. They decided to synthesize tetramethyl ammonium hydroxide and tetrabutyl phosphonium hydroxide by themselves, and compared them. They thought that the former was more satisfactory, so the polymerization process was confirmed. Then, hundreds of kilograms of transparent and clear silicone rubber were produced through self-designed and manufactured pilot equipment. In June 1961, Yang Guangqi, director of the Second Bureau of the Ministry of chemical industry, came to the factory for inspection and was very happy to see the qualified silicone rubber products. Although the price of the rubber produced by this method is relatively high, the silicone rubber that can be mass produced alleviates the urgent need at that time.

Shanghai resin factory, led by Shanghai Chemical Industry Bureau, first set up a 400mm diameter stirring bed in China to produce methyl chlorosilane monomers. It was an enterprise that could provide methyl chlorosilane monomers in batches at that time. After that, in order to accelerate the development of silicone industry in Shanghai and adjust the strength of silicone, Shanghai Chemical Bureau merged Xincheng chemical plant with Shanghai resin plant, and continued to carry out the test of continuous synthesis process device of high temperature vulcanized silicone rubber.

Shanghai Chemical Industry Bureau has set up a special workshop for silicone oil and silicone rubber production in Shanghai resin factory. Shanghai resin factory has successfully trial produced the high vacuum diffusion pump oil, two-component room temperature vulcanized silicone rubber, phenyl methyl silicone oil and so on, which are banned by foreign countries. Shanghai resin factory has become a comprehensive factory that can produce many types of silicone products in China. Although in 1992, due to the adjustment of industrial layout in Shanghai, Shanghai resin factory had to quit the production of methyl chlorosilane and other monomers, and instead purchased monomers and intermediates to produce downstream products. However, Shanghai resin factory has an indelible contribution to the development of organosilicon monomers and organosilicon polymer materials in China.