2.1 preparation of MQ resin

MQ silicone resin is usually prepared by sol-gel process. The main raw materials of M chain are six methyl two siloxane (MM) or three methyl chlorosilane, and Q chain is mainly composed of sodium silicate or sodium tetraethyl orthosilicate (TEOS). Due to the different raw materials of Q-LINK, it is mainly divided into TEOS method and water glass method. The product made from TEOS has good performance, but its cost is high, which limits its application scope; the raw material of water glass process is cheap and easy to obtain, and the product performance is also good, which has a great market value.

2.2 application of MQ silicone in silicone rubber

Silicone rubber has a variety of excellent properties, but its mechanical properties such as compressive strength and tear strength are poor, which can not meet the requirements of the process, so it is necessary to add fillers to modify and strengthen it. When MQ silicone is used as reinforcing filler, it can not only increase the strength of rubber matrix, but also increase the viscosity of the system too fast, which is conducive to the subsequent operation, and the vulcanizate prepared has good transparency.

The organic part of MQ silicone resin can improve its compatibility with silicone rubber and play a role of increasing viscosity; the energy-saving silicon oxygen chain can improve the mechanical strength, cohesive strength, peel strength and high temperature resistance of silicone rubber and play a role of reinforcement. The addition vulcanized silicone rubber is mainly composed of raw rubber containing vinyl, reinforcing filler, crosslinking agent containing hydrogen silicone oil and platinum catalyst. Under the action of platinum catalyst, MQ resin containing vinyl group can chemically combine with raw rubber through hydrosilylation reaction with SIH cross-linking agent, thus forming a three-dimensional network structure to play a reinforcing role. With the increase of MQ silicone content, the hardness, tensile strength, tear strength, adhesion and crosslinking density of silicone rubber gradually increased to the most suitable value. The reason is that the molecular weight of MQ silicone is relatively small, the vinyl content is relatively high, the compatibility and dispersion in silicone rubber are good, and the chemical combination with silicone rubber has taken place. However, when the crosslinking density is too large, the distribution of crosslinking points is uneven, forming stress concentration, and the silicone rubber becomes hard and brittle, which is easy to crack under stress. The curing time increases with the increase of MQ content, because MQ molecule is small and vinyl content is high, it can preferentially react with hydrogen based silicone oil, thus delaying the reaction between silicon hydrogen and vinyl raw rubber until MQ consumption. With the increase of MQ resin content, the dielectric constant of silicone rubber increases to the maximum value and approaches to equilibrium. However, the excessive amount of MQ resin and the excessive crosslinking of silicone rubber restrict the activity of polar groups, which makes the dielectric constant tend to be stable. But the dielectric properties of silicone are still lower than that of rubber.

Condensation type vulcanized silicone rubber is mainly composed of silicone rubber with hydroxyl or alkoxy groups, reinforcing filler, cross-linking agent and catalyst. After the reaction of catalyst or water in the air, the crosslinker hydrolyzes to silanol, which condenses with the silanol of raw rubber to form a three-dimensional network structure and vulcanizes to elastomer. When MQ silicone resin and silicone rubber are mixed, it plays a role of increasing adhesion and strengthening, which makes silicone rubber have excellent mechanical properties. However, when exposed to electromagnetic radiation and vacuum ultraviolet radiation, silicone rubber will age, deform and crack, and its performance will also deteriorate. The main reasons for the decrease of mass and properties of silicone rubber are the escape of unreacted low molecular substances, the fracture of macromolecular network structure, the degradation or crosslinking of molecular chains. In order to make silicone rubber resistant to radiation, radiation resistant fillers, such as nano-TiO2, can be added.

2.3 Application of MQ resin in pressure sensitive adhesive

Silicone pressure-sensitive adhesive is a special adhesive composed of silicone resin (MQ silicone), silicone rubber, catalyst, cross-linking agent and other additives. Silicone pressure sensitive adhesives mainly include solvent type, high solid content type, solvent free type, emulsion type, radiation curing type, resin modified type, biodegradable type and functional type system.