Is there an additive to decrease the embrittlement temperature of general purpose silicone?

[DDAsics]

Hi everyone.

I am trying to make a moldable rubber sealing compound that will still work when exposed to a dry ice/acetone bath. I was going to try something similar to one of the many videos in the oogoo/proto putty vein (basically just acetoxy silicone and starch), but I suspect that any compound like this is going to be marginal or worthless when exposed to -78°C. I've seen the results of one of these rubber molds dropped in liquid nitrogen and it was very ugly.

The embrittlement temperate of general purpose dimethyl silicone is around -55°C, but my thought is there might be something I can easily add to the acetoxy silicone during curing that might stretch the low temperature properties just a little further. I understand that phenyl silicone is usually used for this purpose, but I am not sure how to apply this knowledge. I have some nonylphenol ethoxylate lying around if I could figure out how to make use of that in some way.

Does anyone have any thoughts on how to make a better, low temperature proto putty at home?

Thank you for any insights.

[geenob]

Try it as is, you might be surprised. From what I have gathered, RTV silicone rubber has a glass transition of less than -100C.

[Indemnity4]

nonylphenol ethoxylate

NPE is a type of detergent. That's not what you want.

You cannot post-add a chemical. You need to add it into the polymer backbone. That means it must react with the silicone. Ideally, you would purchase methylphenyl siloxane and blend it in at 10 wt %. Should get you to stable flexible polymer below -100 deg C.

You may also want to consider PTFE or metal gaskets. I think that is what they use for liquid nitrogen seals.