Preparation of Methyl Silicone Resin

Definition of methyl silicone resin

Methyl silicone is a methyl silicone resin dissolved in toluene. This resin has a high SiO2 content and contains about 80% SiO2 after complete oxidation, based on the solid resin content. It is the perfect adhesive for environments above 300 °C.

Characteristics of methyl silicone resin

· It contains 80% SiO2 based on the solid silicone content; · It has high bond strength; · It emits almost no smoke when pyrolysis occurs; · It has outstanding thermal stability.
Preparation of methyl silicone resin The methyl silicone resin can be directly prepared by hydrolysis of methyltrichlorosilane or can be prepared from methyltriethoxysilane.

1 Preparation of methyl silicone resin by hydrolysis of methyltrichlorosilane

Methyltrichlorosilane reacts directly with water to form methyl silicone resin. However, since methyltrichlorosilane contains three active Cl atoms, the hydrolysis polycondensation reaction is extremely fast. In particular, the hydrolysis reaction is carried out under conditions of a high reaction temperature and a large hydrochloric acid concentration, and the obtained methyl silicone resin tends to be a highly crosslinked, insoluble and infusible white solid. In order to produce a soluble meltable product, it is usually necessary to carry out the hydrolysis reaction under milder conditions such as an excess of ice-water or an organic solvent.

1.1 Preparation of methyl silicone resin in ice-water

In an acid-resistant reactor at a stirrer speed of 200 to 240 r/min, 13 parts of an ice-water mixture was added, and stirring was started to lower the temperature of the kettle to 0 °C. Then, 1 part of methyltrichlorosilane was uniformly added at a relatively fast rate. The feeding process must be strictly controlled to a temperature not exceeding 0 °C. After the addition, the mixture was stirred for 1 min, then settled for 4 to 5 h, and the temperature of the sedimentation process was maintained at about 0 °C. After settling, the floc on the surface was removed and the upper hydrochloric acid solution was decanted. Slowly add 70 °C hot water under stirring, and the resin is agglomerated into white powder as the amount of water increases. The coagulum was washed with 70 ° C hot water to neutrality, then air dried or vacuum dried. The resulting methyl silicone resin has the following properties:
Appearance: It is easy to crush white solid
Solubility: Total dissolution in ethanol
Softening point: 40 ~ 47 °C
Gel time (150 °C): 9 min
Storage period (at room temperature): 2 to 7 days

It is heated and kneaded on a twin-roller with a filler such as asbestos or quartz powder to obtain a molding compound excellent in heat resistance and arc resistance. This molding compound is used to process arc-resistant electrical components.

1.2 Preparation of methyl silicone resin in organic solvent

In industrial production, the hydrolysis polycondensation reaction of methyltrichlorosilane is carried out in an organic solvent. Commonly used solvents are: toluene, xylene, isopropanol, n-butanol and the like.
Specifically, a hydrolysis reaction is carried out by adding 600 parts of methyltrichlorosilane to a paste composed of 540 parts of toluene, 118 parts of water, and 27 parts of fumed silica. After the reaction, filtration and acid removal gave 135 parts of methyl silicone resin. The product has a viscosity of 600 mPa at 25 °C. After standing at room temperature for 3 h, it solidifies into insoluble infusibles. If it is placed at a low temperature (below 0 °C) or formulated as a solution, the storage period can be extended to 6 to 12 months.
Such silicone resin  products can be used as a moisture-proof, wear-resistant, weatherproof surface coating for non-transparent materials such as porous stone and wood products.
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