Structure and Classification and Application of MQ Resin

Dec 17, 2020

1. Structure and classification of MQ resin
MQ silicone resin is a kind of silicone resin with unique structure. It is a three-dimensional spherical structure silicone grease produced by CO hydrolysis and polycondensation of organosilicon compounds containing four functional siloxane chains (SiO4 / 2, q) and silicone compounds containing single functional siloxane chains (r3sio1 / 2, m). Its molar mass is generally between 1000 and 8000g / mol. it has the state from viscous fluid to solid powder, hard and brittle, and has a wide range of glass transition temperature (TG).
It is generally considered that MQ silicone resin is a double-layer compact spherical body, in which the core is Si-O chain linked, high density, polymerization degree of 15 ~ 50 cage like SiO2, and the shell is r3sio1 / 2 layer with low density.

MQ silicone resin has many different types because of the different organic group R on the spherical shell
When R is all methyl, it is called methyl MQ silicone resin or MQ silicone resin for short; when part R is h, it is called methyl hydrogen MQ silicone resin; there are also methylphenyl MQ silicone resin, vinyl MQ silicone tree, phenyl MQ silicone resin, fluorine-containing MQ silicone resin, MDQ, MTQ silicone resin, etc. The properties and application range of MQ silicone resin mainly depend on the synthesis process conditions and the type and quantity of organic groups in the molecule, i.e. the ratio of m-link to Q-LINK; the organic group R mainly increases the compatibility with other components, and SiO4 / 2 chain link mainly improves the strength of the composite.

2. Preparation and application of MQ resin
2.1 preparation of MQ resinMQ 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 can be divided into TEOS method and sodium silicate method. The product prepared by TEOS has good performance, but its cost is high, which limits its application scope; the raw material of sodium silicate method is cheap and easy to obtain, and the product has good performance, so it has great market value.

2.2Application 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. Therefore, it is necessary to add fillers to modify and enhance it. When MQ silicone resin is used as reinforcing filler, the strength of rubber matrix can be increased, and the viscosity of the system will not increase too fast, which is conducive to the follow-up operation, and the prepared vulcanizate has good transparency.

The organic part of MQ silicone resin can improve its compatibility with silicone rubber and increase viscosity; silicon oxygen chain can save energy and improve the mechanical strength, cohesive strength, peel strength and high temperature resistance of silicone rubber, which plays a reinforcing role. The addition vulcanized silicone rubber is mainly composed of vinyl containing raw rubber, reinforcing filler, hydrogen silicone oil crosslinking agent and platinum catalyst. In the presence of platinum catalyst, MQ resin containing vinyl group can chemically combine with raw rubber by hydrosilylation reaction with SIH crosslinker, thus forming a three-dimensional network structure for reinforcement. With the increase of MQ silicone resin content, the hardness, tensile strength, tear strength, adhesion and crosslinking density of silicone rubber gradually increase to the optimum value. The reason is that the molecular weight of MQ silicone resin is relatively small, the content of vinyl group is relatively high, the compatibility and dispersion of MQ silicone resin in silicone rubber are better, and MQ silicone resin has chemical combination with silicone rubber. However, when the crosslinking density is too high, the distribution of crosslinking points is uneven and the stress concentration is formed. The silicone rubber becomes hard and brittle, and the silicone rubber is easy to crack under the stress. The curing time increases with the increase of MQ content, which is due to the fact that MQ has small molecule and high vinyl content, which can preferentially react with hydrogen based silicone oil, thus delaying the reaction between silicone hydrogen and vinyl raw rubber until MQ is exhausted. 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 use 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. However, the dielectric properties of silicone resin are still lower than that of ordinary rubber.

Condensed vulcanized silicone rubber is mainly composed of hydroxyl terminated or alkoxy terminated silicone rubber, reinforcing filler, crosslinking agent and catalyst. After the reaction of catalyst or water in the air, the cross-linking agent hydrolyzes to form silanol, and then condenses with silicone hydroxyl group of raw rubber to form three-dimensional network structure, which is vulcanized into elastomer. When MQ silicone resin is mixed with silicone rubber, it can increase viscosity and strengthen, which makes silicone rubber have excellent mechanical properties. However, when exposed to electromagnetic radiation and vacuum ultraviolet radiation, silicone rubber will be aged, deformed and cracked, and its performance will become worse. The main reasons for the decrease of mass and properties of silicone rubber caused by irradiation were the escape of unreacted low molecular substances, the fracture of macromolecular network structure, and the degradation or crosslinking of molecular chains. In order to make silicone rubber radiation resistant, fillers such as nano-TiO2 can be added to the silicone rubber.