According to the commodity form, silicone rubber can be divided into mixed silicone rubber and liquid silicone rubber. Liquid silicone rubber is a kind of self-leveling or thixotropic rubber prepared by linear polyorganosiloxane of medium degree of polymerization as the base polymer filler and various additives, which forms an elastomer after vulcanization. According to its crosslinking vulcanization mechanism, liquid silicone rubber can be divided into two types: condensation silicone rubber and molding silicone rubber.

The curing mechanism of the two kinds of liquid silicone rubber is completely different. Condensation silicone rubber is the use of moisture curing reaction mechanism, that is, the hydroxyl of 107 rubber and silane crosslinking agent condensation reaction in organic tin/organic titanium catalyst and moisture conditions to achieve crosslinking curing; Addition molding silicone rubber is the use of hydrogen siloxane addition reaction mechanism, that is, the action of polysiloxane containing vinyl and polysiloxane containing Si-H in platinum catalyst, through heating (or room temperature) addition reaction, to achieve crosslinking curing.

Due to different curing mechanisms, there are many differences between condensed silicone rubber and added silicone rubber in product packaging form, use mode and performance (Figure 2), such as curing speed, body strength, adhesion, etc., but each has its own advantages.

1. Packaging form. The condensed silicone rubber can be packaged in the form of single component or double component. As a temperature-sensitive product, the catalyst and crosslinking agent need to be separated, usually in the form of two-component packaging, to avoid reactions in the storage process.

2, curing speed. Due to the difference of curing mechanism, there is a great difference in curing speed between condensation silicone rubber and addition silicone rubber. Condensation silicone rubber (mainly refers to a single component) starts from the surface with the help of moisture in the air, and gradually vulcanizes from the surface to the inside. The deep curing is slow, and usually takes 24h or even a week to complete vulcanization. Added silicone rubber can be vulcanized at room temperature or at high temperature. At room temperature, the vulcanization of the compound is consistent with that of the compound.

3, body strength. The mechanical properties of both condensed and formed silicone rubber can be improved by reinforcing fillers such as nano calcium carbonate and gas phase silica, among which the reinforcing effect of gas phase silica is the most obvious.

4. Bonding. Condensation silicone rubber can be bonded to a variety of materials by adding silane coupling agent. Therefore, most of the adhesive fixed sealants in construction, home appliances, lighting, rail transit, photovoltaic and other fields use condensation silicone rubber, which is based on its good adhesion and bonding universality. However, the bonding property of the silicone rubber is far less than that of the condensation silicone rubber, which is related to the low polarity of the molecular chain and the lack of polar groups that can react with the coupling agent.