Hydrosilylation reaction refers to the addition reaction between an organosilicon compound containing a silicon-hydrogen bond and a compound containing an unsaturated bond under certain conditions. One of the important types of reactions. The unsaturated bonds can be carbon-carbon double bonds, carbon-carbon triple bonds, carbon-oxygen double bonds, carbon-nitrogen double bonds, and the like. Among them, the addition reaction of silicon-hydrogen bond and carbon-carbon double bond is the most common hydrosilylation reaction in the silicone industry, and it is the core reaction of many addition-type silicone products.

  For the hydrosilylation reaction, in addition to the hydrosilylation compound and the unsaturated compound, the catalyst is an indispensable component, which plays the role of accelerating the reaction speed, shortening the reaction time and lowering the reaction temperature. The catalysts for the hydrosilylation reaction are mainly compounds and their complexes of VIIIB transition metal elements platinum, palladium, nickel and rhodium in the periodic table, among which the platinum catalyst has the highest catalytic activity and is the most widely used.

  Platinum catalysts used to catalyze hydrosilylation reactions are mainly divided into homogeneous catalysts and heterogeneous catalysts. Among them, the homogeneous catalyst and the reactant are in the same phase, and there is no phase interface. In the hydrosilylation reaction, the homogeneous catalyst generally refers to a liquid catalyst. There are three main types of homogeneous platinum catalysts: the first is to dissolve chloroplatinic acid (H2PtCl6 6H2O) into organic solvents such as ethanol, isopropanol and tetrahydrofuran, and let them interact to form complexes, which are called "Speier catalysts". This catalyst is simple, quick to make and easy to use; the second type of platinum catalyst is a complex of platinum and vinyl double-capped, called Karstedt's catalyst, which has high reactivity and can be stored stably , and has good compatibility with various types of polysiloxanes, and is the most widely used catalyst in addition-type silicone release agents; the third type of platinum catalyst is the formation of chloroplatinic acid in addition to other unsaturated compounds. It also forms complexes with ketones, cyclopentadienes, esters, alcohols, crown ethers, heteroatom-containing crown ethers and polysiloxanes, etc., and is used as a catalyst.


  Homogeneous platinum catalysts have high activity and reaction selectivity, but because they are in the same phase as the reactants, they are difficult to separate after the reaction is completed and cannot be reused, so the cost is high, and at the same time, heavy metal ion pollution may occur. Therefore, scientific researchers solidify the homogeneous catalyst into a heterogeneous catalyst. The so-called solid support of a homogeneous catalyst is to combine a homogeneous catalyst with a solid support by physical or chemical methods to form a special catalyst. Heterogeneous platinum catalysts are in different phases from the reactants, and the common form is that the solid-state catalyst catalyzes the hydrosilylation of liquid mixed reactants. Heterogeneous catalysts for hydrosilylation reaction are mainly divided into two types, traditional heterogeneous platinum catalysts and polymer metal complex catalysts. Among them, traditional heterogeneous catalysts are formed by adsorbing transition metals on inorganic particles such as carbon black and alumina. Such catalysts have high stability and can be recycled and reused, but their catalytic activity and selectivity are low, and the reaction process Higher temperatures and pressures are required. The polymer metal complex catalyst consists of a polymer carrier, a ligand bonded to the carrier and a transition metal. In general, although heterogeneous catalysts have the advantages of high stability and recyclability, their application is limited due to their low activity and selectivity, complicated preparation process, and reduced catalytic activity when they are reused. limit.

 

   There are many substances that can "poison" platinum catalysts, causing their catalytic activity to decrease or even become inactive. For example, organic compounds containing elements such as nitrogen, phosphorus, and sulfur, and ionic compounds containing heavy metals such as tin, lead, mercury, bismuth, and arsenic. Therefore, special attention should be paid to the use of platinum catalysts to avoid exposure of platinum catalysts to these poisoning substances. There are many types and forms of platinum catalysts. Therefore, in the application process, it is necessary to select a suitable platinum catalyst according to the characteristics of the reaction system to obtain the best catalytic effect.

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