With the needs of social development and aerospace environment, higher requirements are put forward for the heat resistance of silicone rubber. In order to meet the needs of special environment and special fields, silicone rubber with good high temperature resistance was prepared. In this regard, in order to meet the needs of different customers for the temperature resistance of silicone rubber, we studied how to improve the temperature resistance of silicone rubber.

We changed the structure of silicone rubber and studied its temperature resistance by adding silica, silicone resin, metal compounds, aromatic compounds and new crosslinking agents.

1. Change the main chain structure

The main reason for the thermal oxidative aging of silicone rubber at high temperature is the fracture and rearrangement of siloxane main chain. Large chain structures such as benzene ring structure in the main chain of siloxane, such as aromatic ring and carbodecaborane, can be used. The introduction of the above structure can greatly improve the high temperature resistance of silicone rubber.

When the main chain structure is polysiloxane structure, and the number of vinyl groups on the side groups of silicone rubber is similar, the thermal stability of silicone rubber is determined by the organic groups on the side chains. It is found that the electron donor groups connected to the side chains are easy to be oxidized, and the electron absorbing groups connected to the side chains are difficult to be oxidized. When phenyl is introduced into the side chains of vinyl polymethylsiloxane, It can greatly improve the thermal stability of silicone rubber.

2. Add white carbon black

Silica is a common reinforcing agent for silicone rubber. Silica is mainly through the silicon warp group on its surface or combined with the Si-O bond on the main chain or the warp group on the end group in silicone rubber, so that the thermal movement of silicone oxygen main chain and O2 are not easy to diffuse in silicone rubber network, When the silicone rubber is thermally oxidized and decomposed at high temperature, the free radical produced reacts with the silicon radical on silica and is consumed, which improves the heat resistance stability of silicone rubber. The thermal stability of silicone rubber was improved by reducing the number of warp groups on the surface of silica.

The effect of silica based on silica on the properties of silicone rubber was studied and analyzed. It was found that the surface content of silica was reduced and the high temperature resistance of silicone rubber was improved by modifying silica with silane coupling agent.

3. Adding silicone resin

Silicone resin and silicone rubber are high molecular polymers with silicone oxygen bond as the main chain, and the side group is connected with methyl and phenyl. It has a highly crosslinked network structure. Due to its structural characteristics, silicone resin itself has excellent high temperature resistance. It is often added to silicone rubber as a reinforcing agent to prevent the release degradation reaction of silicone rubber main chain, so as to improve the high temperature resistance and mechanical properties of silicone rubber.

It is found that when silicone resin is added to high-temperature vulcanized silicone rubber, due to the highly cross-linked network structure of silicone resin, the cyclic degradation reaction of silicone rubber molecular chain is hindered. Therefore, silicone resin can significantly improve the thermal stability of silicone rubber. When phenyl silicone resin is added, the thermal aging properties of silicone rubber can be improved.

4. Adding metal oxide

It was found that metal oxides were added to the silicone rubber matrix to hinder the oxidative degradation and crosslinking reaction of silicone rubber side groups. Due to the crosslinking and hardening of silicone rubber system caused by chain growth and chain termination reaction, its action mechanism is exactly the same. Free radicals are generated in the oxidation process of silicone rubber, and metal ions are reduced in the process of capturing free radicals, which prevents the chain growth reaction and improves the high temperature resistance of silicone rubber. In order to solve the problem of metal oxide dispersion in silicone rubber, silane coupling agent is usually used to modify it to improve the dispersion of metal oxide in silicone rubber matrix.

5. New crosslinking agent

The results show that the structure of crosslinking system, i.e. crosslinking agent, has a great influence on the heat resistance and mechanical properties of silicone rubber. As far as we know, addition molding RTV silicone rubber is widely used at present, because there will still be impurities in the colloid after condensation RTV silicone rubber is cured under high temperature environment, which will promote the degradation of silicone rubber molecules. Therefore, To some extent, the selection of new crosslinking system plays an important role in improving the heat stability and mechanical properties of silicone rubber.