Chemistry Reference
In-Depth Information
Table 1.1.
BACKBONE AND SIDE CHAINS ON SOME ILLUSTR ATIVE
POLYSILOX A NES
Polymer
Backbone
Side chains
Characteristics
Poly(dimethylsiloxane)
Si-O-
CH
3
CH
3
Most extensively used
polysiloxane
Poly(phenylmethylsiloxane)
Si-O-
C
6
H
5
CH
3
Suppressed crystallinity
and improved radiation
resistance
Poly(vinylmethylsiloxane)
Si-O-
C
2
H
3
CH
3
Unsaturation sites
simplify cross linking
Siloxane-silarylene polymers
Si-O- and
Si-(
m
or
p
phenylene
)
CH
3
CH
3
Stiffer backbones useful
in some applications
Siloxane-silalkylene polymers
Si-O- and
Si-C-
CH
3
CH
3
Reduced thermal stability
apparently largely uncharacterized material of this type. This latter work
resulted in a number of collaborations with the General Electric Company
and the Mellon Institute focused on siloxane-based, thermally resistant
coatings. Possible use in fiberglass insulation in submarine motors helped
accelerate work in this area, including construction of a siloxane pilot
plant based on Grignard reactions at the Mellon Institute in 1940.
In the case of the direct process, only one of the resulting products can
be used to obtain siloxane polymers.
28
Table 1.1 describes some of these
products.
1.3 NOMENCLATURE
In most of the literature, siloxane terminology consists simply of specifying
the side groups and then the backbone. For example, the polymer having the
repeat unit [-Si(CH
3
)
2
O-] is called poly(dimethylsiloxane), and that having
the repeat unit [-Si(CH
3
) (C
6
H
5
) O-] is called poly(phenylmethylsiloxane).
Closely related polymers are the poly(silmethylenes) of repeat unit
[-SiRR'CH
2
-] and the poly(siloxane-silphenylenes) of repeat unit
[-SiRR'OSiRR'C
6
H
4
-], in which the second oxygen atom in the doubled
repeat unit is replaced by a phenylene group.
Because certain structures and structural segments appear over and
over again in the siloxane area, several abbreviations are used in specialized
areas of the literature.
28, 29
The monofunctional unit R
3
SiO
0.5
is designated
