No. 1031 - Miljøstyrelsen

Cyclic siloxanes with other functional groups, e.g. methylphenylcyclosiloxanes,
are used for fewer applications. Among other applications, cyclic methylsiloxanes
are widely used in cosmetic products, in which cyclic siloxanes or
mixtures of the compounds are known under the name "cyclomethicone". According
to the 2000 version of the INCI list (Annex 1) cyclomethicone is synonymous
with octamethyltetrasiloxane. Producers, however, use the term
more widely, e.g. the UK producer Basildon Chemicals has four types of cyclomethicone,
either as pure D4 or D5 or as different mixtures of D4, D5 and
D6 (http://www.baschem.co.uk/downloads/cy56.pdf).
Silanes
Silanes are used as precursors in the production of siloxanes and are used as
cross-linking agents for formation of silicone elastomers and resins (described
later in this section).
Silanes are silicon compounds, both organic and inorganic. The siloxanes are
actually one of five subgroups of silanes, but often the term "silanes" is used
for designating the other groups. The other groups are those containing Si–H
bonds (hydride functional silanes), Si–X (halosilanes), Si–C (organosilanes),
and Si–OR (silicon esters).
Both linear and cyclic polysiloxanes are generally
produced by reacting organodichlorosilanes with
water (Ullmann 2003). Besides their use in production
processes, organodichlorosilanes may
also be present in products for polymerisation of
silicones by the users.
Silsesquioxanes
The silsesquioxanes are a subgroup of the siloxanes. The term silsesquioxanes
denotes a polymer in which the ratio of silicon and oxygen in each moiety (sequence)
is 1.5 (latin: sesqui). Many commercial silicones include silsesquioxanes.
The polysilsesquioxanes are highly
branched polymers and difficult to
describe. In their most simple form
they can be described by a ladder
structure, more complex structures
are designated "cage structures" and
"random structures".
They are mainly used for silicon resins,
in particular for paints and coatings.
Dichlorodimethylsilane
Fluids, elastomers and resins
Silicones can be classified into three types depending on the length of the
backbone, the extent of crosslinking and the type and number of organic
groups attached to the silicon atoms:
Cl
O
CH3
Si CH3
Cl
Polymethyl silsesquioxane
H3C
H3C
CH3
Si
O
Si
CH3
O
CH3
Si CH3
O
Si CH3
CH3
n
21