Cure systems for silicone polymers

Silicone fluids can be used "as supplied." In other words, their properties are fully developed. Silicone gels, elastomers, and resins, however, may need to be crosslinked (or cured) to achieve their final properties. This requires the presence of a crosslinker – a silicone molecule with multiple functional sites that can react or link with another silicone polymer.

Under the right conditions (heat, humidity, or ultraviolet light) – and in the presence of the crosslinker and a catalyst – the individual polymer chains will link together to form a more complex material.

Depending on the base polymer, the crosslink density, and the presence of any reinforcing fillers, this material can range from a rigid film to a flexible rubber or a spongy gel.

Crosslinking or cure reactions for silicones

There are three crosslinking reactions for reactive silicone polymers:

• A peroxide-initiated free radical reaction, which is activated by heat
  • Peroxide cure
• A condensation reaction, which takes place in the presence of a tin salt or titanium alkoxide catalyst
  • Heat cure
  • RTV moisture cure
• An addition reaction, which is generally catalyzed by a platinum or rhodium complex
  • Temperature-activated
  • Photo-initiated

For an in-depth discussion of silicone crosslinking reactions, read Section 5 of the Silicone Chemistry Overview. (PDF Size 101KB)

One part or two?

One- or two-part cure systems are selected based on the environment they will be used in, the method of application, the expected rate of use, and other application requirements. Compare the typical uses, advantages and disadvantages of one- vs. two-part silicone cure systems.