The basic principle of fluorosilicone rubber products.pacifier cast wholesale

　　Silicone rubber is currently an indispensable synthetic material in the market of various industries in my country. It can be used in any industry to form silicone rubber products with strong tensile resilience, aging and temperature resistance and other properties. A new type of active material, it is mainly composed of a variety of molecular chains, but which molecular chains are polymerized? Today we will analyze its more primitive basic principles!

　　Cyclosiloxane is an important raw material in the modern silicone industry. Similarly, cyclosiloxane (trifluoropropylmethylcyclotrisiloxane (referred to as D3F)) is an important raw material for fluorine-containing silicone rubber. Any industry can get different effects in the form of silicone raw materials and silicone finished products!

　　Due to the coordination bond formed by the silicon and oxygen atoms of cyclosiloxane D3F, the bond energy is large, and it is impossible to homogenize under normal conditions. However, due to the small electronegativity of the silicon atom (Si: 1.8) and the large electronegativity of the oxygen atom (O: 3.5), the Si+O- bond is a polar bond, which can be used in ionic media such as acids and bases. Catalytically easily cleaved to form chain polymers

　　According to the acidity and alkalinity of the catalyst, the ring-opening polymerization mechanism of cyclosiloxane is different, which can be divided into anionic ring-opening polymerization and cationic ring-opening polymerization.

　　Anionic polymerization mechanism

　　Anion-catalyzed ring-opening polymerization is the process of ring-opening polymerization of cyclic siloxanes under the action of alkaline catalysts to form linear polysiloxanes.

　　1.1 Features

　　(1) The electronegativity of silicon atoms is small, and they are easily attacked by alkaline catalysts;

　　(2) The concentration of alkali catalysts is usually very low (0.001~1%), especially the preparation of high molecular weight polysiloxanes requires the use of low concentration catalysts;

　　(3) The speed of the ring-opening reaction is extremely fast, and it is rapidly polycondensed into a high-viscosity polymer, and the reaction is not easy to control.

　　(4) Because the base catalyst produces few active centers, it is very sensitive to a small amount of impurities. Acidic substances can destroy the active center to terminate the reaction, so the presence of a small amount of water, CO2, etc. can also coordinate with the active center to inhibit the reaction. Especially water, the interference is greater. Therefore, before the polymerization, the raw materials and the reactor should be fully dried, and the water generated by the reaction should be continuously discharged by vacuum during the polymerization, so that the molecular weight can grow.

　　1.2 Aggregation process

　　The anionic ring-opening polymerization process is mainly composed of four stages:

　　(1) In the chain initiation stage, a reaction center is formed;

　　Because of the low electronegativity of the silicon atom, the OH-anion in the base catalyst is coordinated with the 3d orbital of the silicon atom of the cyclosiloxane, resulting in the redistribution of the electron cloud density, and the Si-O bond can be broken under heating conditions (ring opening ) to generate linear siloxane oligomers containing anions at the chain ends.

　　(2) Chain growth stage;

　　The new cyclosiloxanes continue to be attracted by the anion-containing active centers generated by the chain initiation, and by initiating ring opening to form longer chain active centers, thus continuously attracting more cyclosiloxanes and making the chain grow.

　　Under the action of anion catalysts, the chain growth process is a reversible reaction process, and the whole process is accompanied by the occurrence of bite back and degrades into larger siloxane rings.

　　(3) Chain termination stage;

　　The chain-like active center reacts with the monofunctional species to terminate the chain growth reaction. If no end-capping agent is added during the polymerization, the prepared product is a hydroxyl-terminated linear polysiloxane

　　(4) Chain transfer forms new active sites.

　　When the chain-like active center attacks the Si-O bonds on different linear polysiloxane chains, a chain rearrangement reaction will occur, that is, a chain transfer reaction. Therefore, after the anionic catalyst is introduced into the siloxane ring, each molecule can participate in a series of reactions such as growth, ring formation and rearrangement until the reaction reaches equilibrium.

　　Cationic polymerization mechanism

　　Cationic ring-opening polymerization is the ring-opening polymerization of cyclosiloxanes under the action of an acidic catalyst.

　　2.1 Aggregation characteristics

　　The characteristics of cationic polymerization are that the reaction is mild and controllable, and it is suitable for generating low molecular weight polymers.

　　2.2 Aggregation process

　　The cationic polymerization process mainly consists of four stages:

　　(1) In the chain initiation stage, a reaction center is formed;

　　The ring-opening reaction opens the silicon-oxygen bond to form an active center.

　　Due to the large electronegativity of the oxygen atom, it is generally believed that when an acid catalyst is used to catalyze the ring-opening polymerization of cyclosiloxane, the H+ in the acid catalyst is first coordinated with the unshared electron pair of the oxygen atom to break the Si-O bond (ring-opening). ), resulting in a linear siloxane active center containing a cation at the chain end.

　　(1) Chain growth stage;

　　Cyclic siloxanes are attracted by the active centers generated by the chain initiation, and by initiating new ring openings to form longer chain active centers, thus continuously attracting more cyclic siloxanes and making the chain grow.

　　(3) Chain termination stage;

　　The active center reacts with the monofunctional species to terminate the chain growth reaction.

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