Curing of "odorless" silicone caulk

[Stephen Tashi]

What causes the "odorless" type of silicone caulk to cure once it has been extruded from its tube, but allows it to remain uncured while it is in the tube.

My understanding is that the type of silicone caulk that smells like vinegar cures outside the tube because it is exposed to moisture - but what activates the cure of caulk that is "odorless" or "low oder" or "GE silicone II" ?

 

[Borek]

Most likely it is still a moisture that is necessary for polymerization.

 

[Stephen Tashi]

There are many water based things that can be mixed with non-odorless silicone caulk that make it cure quickly - such as acrylic paint, glycerine, soapy water. (Videos on the web show doing this to make flexible molds. I've tried these methods and they do work.) However, when those things are mixed with GE Silicone II caulk, it either doesn't cure or cures to a very weak material. This is why I'm curious about curing process for odorless silicone caulk.

 

[TeethWhitener]

I don't know the exact process, but when in doubt, check the MSDS:
http://www.homedepot.com/catalog/pdfImages/2d/2d9622c5-268d-4ab0-8dce-32dd186b8b72.pdf
The main component is MPDMS, which is formed by a condensation reaction of PDMS and the trimethylsiloxane. The HMDS is probably an initiator (it tends to methylate SiOH groups). But HMDS is quite reactive with water. It's possible that humid air is enough to start breaking down the HMDS to initiate polymerization, whereas mixing water directly simply destroys all the HMDS at the outset. But again, this is just a guess.

Edit: abbreviations are as follows.
HMDS = hexamethyldisilazane
PDMS = polydimethylsiloxane
MPDMS = methoxypolydimethylsiloxane
For completeness:
MSDS = material safety data sheet
SiOH = silanol functional group