How to improve the resilience of fluorosilicone rubber?

The theoretical principle of improving the resilience of fluorosilicone rubber

1. The theory proposed in this assumption is that the rubber molecular backbone needs enough space to contract freely in order to have good resilience.

2. The method to improve the resilience of fluorosilicone rubber is to increase the length of the crosslinking bond.

2.1 Allyl methyl cyclotetrasiloxane (D4CH2CH=CH2) is used instead of vinyl methyl cyclotetrasiloxane (D4Vi) used in silicone rubber to extend the length of cross-linking bonds.

2.2 Add an appropriate amount of cross-linking extender (e.g. CH=CH2CH2=CH) to increase the length of the cross-linking bond.

Model analysis

At present, the crosslinked bond after vulcanization of silicone rubber is SiCH2CH2CH2CH2Si. The length of the crosslinked bond is 0.8nm.It's like a lot of silicon oxygen chains being held together by a certain number of cross-links.The silica chain is filled with methyl (0.32nm in length) and trifluoropropyl (0.63nm in length), and the length of the filled group also reflects the size of the volume to some extent.Trifluoropropyl has a large volume and the length of the cross-linked bond is not long enough, so the main chain is squeezed and cannot rotate and contract freely.So resilience is not ideal.

The figure below shows the model after vulcanization:

It can be seen that the length of the crosslinking bond is not enough, which causes the silicon oxygen chain to be squeezed, and the crosslinking bond is in the state of pulling force, which affects the rubber resilience.

Molecular model of raw rubber: Vinyl is blocked by trifluoropropyl, so silicone rubber vulcanization rate will be slower than normal silicone vulcanization.And there will be parts of the vinyl that won't react.

Therefore, using allyl methyl cyclotetrasiloxane or allyl methyl cyclotetrasiloxane instead of vinylmethyl cyclotetrasiloxane used in silicone rubber can improve the vulcanization speed and resilience of fluorosilicone rubber.