1. What are the chemical properties of hydroxyl silicone oil?
Hydroxyl silicone oil not only has similar properties to dimethylsiloxane (such as methyl silicone oil), but also possesses special properties brought about by the active silanol groups. When reacting with organic alkoxysilanes, organic acylsilanes, and amino silanes under the action of acidic or alkaline media, it can undergo condensation reactions to form high-molecular polymers; and react with borate esters, titanate esters, silicate esters, and silicon-hydrogen bonds to generate cross-linked bonding products. Hydroxyl silicone oil can be synthesized with aminoalkyl silanes (such as coupling agent KH-550 or coupling agent KH-602) to form amino silicone oil. The reaction product is a silicone oil with increased molecular weight, where the aminoalkyl is grafted on the side chain of the polysiloxane chain. The ratio of raw materials for the reaction depends on the ammonia value of the prepared amino silicone oil. For example, when using KH-602, a product with an ammonia value of 0.3 uses 96.67% of hydroxyl silicone oil and 3.33% of KH-602.
II. How are hydroxyl silicone oils produced?
1. Catalytic polymerization method: This is the commonly used industrial production method. Using octamethylcyclotetrasiloxane (D4) or dimethylcyclotetrasiloxane (DMC) as the starting raw material, water as the end-capping agent, and under the catalysis of acids, bases, ion exchange resins, and acidic clay, they undergo polymerization to obtain. When using D4 as the raw material, the reaction process is shown in "The process of synthesizing hydroxyl silicone oil by catalytic polymerization". Method: Add octamethylcyclotetrasiloxane (D4) or dimethylcyclotetrasiloxane (DMC), catalyst (solid-supported catalysts, etc.), and water in the required ratio to the reactor. Then, heat up for the in-situ polymerization reaction, and sample to detect the conversion rate of the raw materials. When it reaches over 80%, discharge and obtain the crude silicone oil product. Put the crude silicone oil into an evaporator above 100℃, conduct continuous distillation under 3 kPa to remove low-molecular substances and obtain the dimethyl hydroxyl silicone oil product.
2. Hydrolysis method: Obtained by hydrolyzing dimethyl dichlorosilane or dimethyl dialkoxysilane, or by reacting dimethyl dichlorosilane with methanol. Principle: Dimethyl dichlorosilane first hydrolyzes, with one chlorine atom being hydrolyzed first, and the remaining chlorine atom hydrolyzing more slowly.
Method:
(1) Dropwise add the measured dimethyl dichlorosilane to the 24% ammonia water, stir for hydrolysis, and quickly separate the oil phase from the reaction system. Separate the oil phase, dry it with anhydrous calcium chloride, then de-colorize with activated carbon, and dehydrogenate by the gas extraction method to obtain a colorless transparent liquid, which is the small molecule hydroxyl silicone oil. It contains approximately 50-80% linear substances and 20-50% cyclic substances mixed together.
(2) Add the measured organic solvent, water, and alkaline neutralizer to the enamel hydrolysis reactor. Start stirring, and directly slowly add dimethyl dichlorosilane to the reactor at a temperature below 10℃ for hydrolysis. After adding all the materials, continue stirring for 20 minutes, stop the reaction, and let it stand to separate layers. Release the wastewater, dry the material, remove solvents and filter to obtain the dimethyl hydroxyl silicone oil product.