Cross-linking agent silicone rubber

Chen, D. Yi, S. Wu, W. Zhong, Y. Liao, J. Huang, C., Synthesis and Characterization of Novel Room Temperature Vulcanized (RTV) Silicone Rubbers Using Vinyl-POSS Derivatives as Cross Linking Agents. Polymer 2010, 51, 3867-3878. 

The chains can be cross-linked to form rubbers if suitable reactive groups are incorporated in the molecule (Moretto et ah, 2002). There are two major classes of room-temperature vulcanizing (RTV) rubbers (Thomas, 1993). The majority (both two-part and one-part) set by a condensation reaction (Figure 13.4, Table 13.2). Two-part RTV-2 rubbers are formulated of the silicone polymer (MW 10,000) with -OH at either end mixed with a filler (usually finely divided silica), a small amount of water and frequently some unreac-tive silicone oil to rednce viscosity of the mix and increase flexibility of the rubber the cross-Unking agent (commonly TEOS) and a dialkyl tin catalyst. 

TABLE 13.2 Some Typical Cross-Linking Agents, CH3-Si(-Y)3, of Condensation-Type Silicone Rubbers... 

One-part type For one-part-type siHcones, both the catalyst and the cross-linking agent are incorporated in the base compound at the time of manufacture, which involves compounding a silanol-stopped siHcone polymer with an excess of cross-linker. The one-component silicones typically cure with moisture. Exposure to atmospheric moisture causes further curing of the silicone rubber to take place. Diffusion of moisture into the rubber progresses vulcanization from the surface inward. One-part component type silicones are excellent adhesive sealants and can be formed in place as gaskets. They can also be used to form films by solvent dispersion. 

A small amount of curing agent is required for the preparation of cross-linked or vulcanised silicone resins and silicone rubber. This has the desired effect either during the polymerisation or later, during the baking or vulcanisation steps. 

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