Silicone Crosslinking Technical Information
Crosslinking or curing is initiated by crosslinking chemicals, which react with the vinyl groups present in the VMQ and PVMQ polymer chains. The nature of this reaction depends to a large extent on the chemicals’ properties: it can be fast or slow, complete or incomplete, more sensitive to temperatures or more resilient to external influences.
There are two different curing processes employed: peroxide curing and platinum-catalyzed addition curing. A brief explanation of both is given below.
Liquid silicone rubbers’ are always platinum catalyzed. For solid silicone rubbers, however, either curing system can be employed.
The peroxide group produces an oxygen free radical. A reactive free radical is formed on the vinyl. The free radical attaches itself to another polymer chain and forms a bridge. The free radical chain reaction then continues.
The platinum center has one free coordination site. Interaction with the platinum center activates the double bond. The vinyl group crosslinks by transforming the double bond, creating a single bond to a polymer chain; in this case, to a crosslinker molecule containing Si-H groups. The catalyst becomes free and is again available for further crosslinking.