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 tetraethyl orthosilicate method and sodium silicate method. The product made from tetraethyl orthosilicate has good properties, but its high cost limits its application. The raw material of sodium silicate method is cheap and easy to obtain, and the product has good properties, which has great market value.


Application of MQ Silicone Resin in Silicone Rubber
Silicone rubber has many excellent properties, but its mechanical properties such as compressive strength and tear strength are poor, which can not meet the requirements of the process. It needs to be modified and strengthened by adding fillers. When MQ silicone resin is used as reinforcing filler, it can not only increase the strength of rubber matrix, but also not make the viscosity of the system increase too fast to facilitate subsequent operation, and the prepared vulcanizate has good transparency.


The organic part of MQ silicone resin can improve its compatibility with silicone rubber and play a tackifying role. The energy-saving silicone oxygen chain can improve the mechanical strength, cohesive strength, peeling strength and high temperature resistance of silicone rubber, and play a reinforcing role. Additive vulcanized silicone rubber is mainly composed of raw rubber containing vinyl group, reinforcing filler, hydrogenated silicone oil crosslinking agent and platinum catalyst. Under the action of platinum catalyst, MQ resin containing vinyl group can chemically combine with raw rubber by hydrosilylation reaction with SiH crosslinking agent, thus forming a three-dimensional network structure to reinforce it. With the increase of the amount of MQ silicone resin, the hardness, tensile strength, tear strength, adhesion and crosslinking density of silicone rubber gradually increase to the optimum value. The reason is that MQ silicone resin has relatively small molecular weight, relatively high vinyl content, good compatibility and dispersion in silicone rubber, and chemical bonding with silicone rubber. However, when the crosslinking density is too high, the distribution of crosslinking points is not uniform, resulting in stress concentration. Silicone rubber becomes hard and brittle, and is liable to rupture under stress. The curing time was prolonged with the increase of MQ dosage, which was due to the small MQ molecule and high vinyl content, which could react preferentially with hydrogen-based silicone oil, thus delaying the reaction between silicone and vinyl raw rubber until MQ was depleted. With the increase of MQ resin content, the dielectric constant of silicone rubber increases to the maximum and approaches equilibrium. However, the excessive amount of MQ resin and the excessive cross-linking of silicone rubber limit the activity of polar groups, thus the dielectric constant tends to be stable. But the dielectric property of silicone resin is still lower than that of ordinary rubber.


Condensed vulcanized silicone rubber is mainly composed of silicone rubber containing hydroxyl or alkoxy end groups, reinforcing filler, crosslinking agent and catalyst. After the reaction of catalyst or water in air, the cross-linking agent hydrolyzed to form silanol, which resulted in the condensation reaction between the silica hydroxyl group of raw rubber to form a three-dimensional network structure and vulcanized into elastomer. When MQ silicone resin is mixed with silicone rubber, it plays a role of tackifying and reinforcing, which makes silicone rubber have excellent mechanical properties. However, when it is exposed to electromagnetic radiation and vacuum ultraviolet radiation, silicone rubber will age, deform, crack and its properties will deteriorate. The main reasons for the decrease of silicone rubber quality and properties caused by irradiation are the escape of unreacted low molecular substances, the breakage of macromolecular network structure, the degradation or crosslinking of molecular chains in vulcanizates under irradiation. In order to make silicone rubber radiation-resistant, radiation-resistant fillers, such as nano-titanium dioxide, can be added to it.