Chemistry Reference
In-Depth Information
7.14.3 Polysiloxane Coating Resins
These materials are usually prepared in two stages. In the first one, low molecular weight
intermediates are formed. In the second one, the intermediates are reacted with other resins
possessing functional groups, like alkyds, polyesters, or acrylic resins. The most common low
molecular weight intermediates are:
R
R
HO
Si
O
Si
O
R
Si
and
O
Si
O
O
x
O
Si
O
R
Si
R
O i
O
OH
R
where
x ΒΌ
3-6.
7.14.4 Fluorosilicone Elastomers
The elastomers are based on polysiloxanes that contain trifluoropropyl methyl siloxane units. The
materials are used as sealants, elastomers, and fluids for aerospace applications. The monomers are
prepared according to the following scheme:
H
Cl
Si
Cl
Cl
Cl
F
F
F
Si
HF
Cl
Cl
F
F
Cl
F
The above dichloro silane is converted to a cyclic trimer:
F
F
F
Si
O
O
F
Si
Si
F
F
F
F
O
F
Ring opening polymerizations with basic catalysts convert the trimers to polymers at elevated
temperatures. Some vinyl silane is usually copolymerized with the material for subsequent cross-
linking. These elastomers are reported to be capable of maintaining their original strengths at
temperatures as high as 205
C for long periods of time.
