Siloxanes Indexing Policy

General Information

Siloxanes prepared by hydrolytic polymerization of alkoxysilanes or halosilanes typically have been indexed in the CA^SM/CAplus^SM databases at the controlled-term heading SILOXANES AND SILICONES, with no polymer registration. Siloxanes described only in terms of structural repeating units (SRUs) also have been indexed at this heading with no polymer registration.

Beginning June 1994 (Vol. 121) indexing policies were modified and relaxed to allow structural representation and machine registration of siloxanes previously handled only as text terms in the CA database. CAS recognizes that these policy changes, which focus on monomer-based polymer registrations, do not fully answer user needs for structure specificity as could be represented by SRU-type registrations. It is our desire to provide such specificity as we enhance the CAS REGISTRY^SM capability in the future. The changes described below provide structures that can be registered currently with the result that structural information is moved from the CA database to the REGISTRY database, where we believe it affords improved searchability.

The following areas are affected by these changes:

1. Siloxanes prepared by hydrolytic polymerization of alkoxysilanes.
2. Siloxanes prepared by hydrolytic polymerization of halosilanes.
3. Siloxanes described only in terms of single-unit SRUs of the type (-O-SiRR'-)n (R, R' = monovalent radical).
4. Siloxanes described only in terms of multiunit SRUs of the type (-O-SiR2-)x(-O-SiR'2-)y or (-R2SiO-)x(-R'SiO1.5-)y (R,R' = monovalent radical).
5. Silsesquioxanes prepared by hydrolytic polymerization of alkoxy- or chlorosilanes.
6. Ceramers (hybrid organic-inorganic networks) prepared by hydrolytic polymerization (sol-gel process) of tetraalkoxysilanes with alkoxysilanes containing organic moieties, which may be trialkoxysilyl-terminated organic polymers.
7. End groups for siloxane SRUs.
8. Copolymers containing siloxane components.
9. Trade names for siloxanes and silsesquioxanes.
10. Silicone rubbers.

An important aspect of the policy change is the acceptance of water in the structure representation for siloxanes and silsesquioxanes prepared by the hydrolytic polymerization of halosilanes. Another significant aspect is the acceptance of hydroxysilanes as standard monomer assumptions for providing monomer-based polymer registrations from siloxane SRU representations of types (3) and (4).

Also note that descriptions for substituents on the siloxane backbone are no longer provided routinely at the controlled-term headings SILOXANES AND SILICONES and SILSESQUIOXANES when a polymer registration is possible. Such information is reflected in the structural representation in the Registry File and in the Chemical Substance Index entries.

1. Alkoxysilane-based Siloxanes

Siloxanes from the hydrolytic polymerization of alkoxysilanes receive a monomer-based polymer registration and a polymer class entry in the CA database at the controlled-term heading SILOXANES AND SILICONES. An additional entry is made for the SRU when it is of the single-unit type.

Example 1: A siloxane from hydrolytic polymerization of Me2Si(OMe)2.

Registry File: Silane, dimethoxydimethyl-, homopolymer [25498-04-8]

Poly[oxy(dimethylsilylene)] [9016-00-6]

CA File: Siloxanes and Silicones

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Example 2: A siloxane from hydrolytic copolymerization of Me2Si(OMe)2 with
Ph2Si(OMe)2.

Registry File: Silane, dimethoxydimethyl-, polymer with
dimethoxydiphenylsilane

CA File: Siloxanes and Silicones

2. Halosilane-based Siloxanes

For siloxanes from the hydrolytic polymerization of halosilanes (mainly chlorosilanes), water is included in the polymer registration and is incorporated in the polymer name by use of the term "hydrolytic" (e.g., Silane, dichlorodimethyl-, homopolymer, hydrolytic). These measures are necessary in order to differentiate siloxanes from polysilanes, which are also prepared from chlorosilanes, but under nonhydrolytic reaction conditions (e.g., Silane, dichlorodimethyl-, homopolymer). Entries are made for the monomer-based polymer and at the controlled-term heading SILOXANES AND SILICONES. An additional entry is made for the SRU when it is of the single-unit type.

Example 1: A siloxane from hydrolytic polymerization of Me2SiCl2.

Registry File: Silane, dichlorodimethyl-, homopolymer, hydrolytic
[158158-00-0]

Me
|
(Cl-Si-Cl . H2O)x
|
Me

MF (C2H6Cl2Si . H2O)x

Poly[oxy(dimethylsilylene)] [9016-00-6]

CA File: Siloxanes and Silicones

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Example 2: A siloxane from hydrolytic copolymerization of Me2SiCl2 with
Ph2SiCl2.

Registry File: Silane, dichlorodimethyl-, polymer with dichlorodiphenylsilane,
hydrolytic [156665-92-8]

Me Ph
| |
(Cl-Si-Cl . Cl-Si-Cl . H2O)x
| |
Me Ph

MF (C12H10Cl2Si . C2H6Cl2Si . H2O)x

CA File: Siloxanes and Silicones

3. Single-unit Siloxane SRUs

Siloxanes described only in terms of single-unit SRUs are indexed with an SRU entry and a controlled-term entry at SILOXANES AND SILICONES. In addition, a monomer-based polymer entry is made by assuming hydroxysilanes for the monomers.

Example: A siloxane with the author representation (-OSiMe2-)n or
"poly(dimethylsiloxane)" with no preparative information and no
end groups specified.

Registry File: Poly[oxy(dimethylsilylene)] [9016-00-6]

Silanediol, dimethyl-, homopolymer [31900-57-9]
(polymer based on assumed monomer)

CA File: Siloxanes and Silicones

4. Multiunit Siloxane SRUs

Siloxanes described only in terms of multiunit SRUs of the type (-O-SiR2-)x(-O-SiR'2-)y or (-R2SiO-)x(-R'SiO1.5-)y (R,R' = monovalent radical) cannot be registered as an SRU. They are indexed with a controlled-term entry at SILOXANES AND SILICONES and with a monomer-based polymer entry, made by assuming hydroxysilanes as monomers.

Example: A siloxane represented by the author as (-OSiMe2-)x(-OSiPh2-)y
with no preparative information given.

Registry File: Silanediol, dimethyl-, polymer with diphenylsilanediol
[156048-34-9]
(polymer based on assumed monomers)

CA File: Siloxanes and Silicones

5. Silsesquioxanes

For silsesquioxanes (siloxanes with repeating RSiO1.5 units), entries are made at the monomer-based polymer [based on the actual or assumed (hydroxysilane) monomer] and at the controlled-term heading SILSESQUIOXANES. Ladder-type SRU entries are made for silsesquioxanes represented by a single RSiO1.5 repeat unit, e.g., when R = Me.

Example 1: Me silsesquioxane from hydrolytic polymerization of MeSi(OMe)3.

Registry File: Silane, trimethoxymethyl-, homopolymer [25498-03-7]

Poly[(1,3-dimethyl-1,3:1,3-disiloxanediylidene)-
1,3-bis(oxy)] [153315-80-1]

Me
|
--O-Si--
|
( O )
| n
--O-Si--
|
Me

MF (C2H6O3Si2)n

CA File: Silsesquioxanes
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Example 2: Me silsesquioxane from hydrolytic polymerization of MeSiCl3.

Registry File: Silane, trichloromethyl-, homopolymer, hydrolytic [156894-09-6]

Cl
|
(Cl-Si-Cl . H2O)x
|
Me

MF (CH3Cl3Si . H2O)x

Poly[(1,3-dimethyl-1,3:1,3-disiloxanediylidene)-
1,3-bis(oxy)] [153315-80-1]

Me
|
--O-Si--
|
( O )
| n
--O-Si--
|
Me

MF (C2H6O3Si2)n

CA File: Silsesquioxanes
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Example 3: A silsesquioxane represented as (-MeSiO1.5-)n with no
preparative information.

Registry File: Silanetriol, methyl-, homopolymer [104133-11-1]
(polymer based on assumed monomer)

Poly[(1,3-dimethyl-1,3:1,3-disiloxanediylidene)-
1,3-bis(oxy)] [153315-80-1]

Me
|
--O-Si--
|
( O )
| n
--O-Si--
|
Me

MF (C2H6O3Si2)n

CA File: Silsesquioxanes

6. Ceramers

Ceramers are hybrid organic-inorganic networks obtained by the sol-gel process based on the hydrolytic polycondensation of tetraalkoxysilanes with alkoxysilane-containing organic moieties. Such networks are indexed as monomer-based polymers when the components are specified and all are involved in the polycondensation.

Example: A ceramer prepared from (EtO)4Si and (EtO)3Si[O(CH2)4]
nOSi(OEt)3 using the sol-gel process.
Registry File: Silicic acid (H4SiO4), tetraethyl ester, polymer
with .alpha.-(triethoxysilyl)-.omega.-[(triethoxysilyl)oxy]-
poly(oxy-1,4-butanediyl)
OEt OEt OEt
| | |
[EtO-Si-OEt . EtO-Si-(OCH2CH2CH2CH2)n-O-Si-OEt]x
| | |
OEt OEt OEt
MF (C8H20O4Si . (C4H8O)nC12H30O7Si2)x
CA File: Siloxanes and Silicones (silicate-)

7. End Groups for Siloxane SRUs

End groups for siloxane SRUs are not assumed except in the case of nonreactive commercial siloxanes. For such siloxanes, Me3Si- end groups are commonly incorporated to provide stability and are a standard assumption. Hydroxy end groups are used for siloxane SRUs only when so indicated or implied.

8. Siloxane Components in Copolymers

When registrable siloxanes appear as components in copolymers, they are included in the copolymer either as terminated SRUs (homopolymer siloxanes) or, in the case of copolymer siloxanes, as the identified or assumed (hydroxysilanes) monomers.

Example 1: A block siloxane-polyurethane prepared from H(OSiMe2)
nOH toluene diisocyanate, and 1,4-butanediol.

Registry File: 1,4-Butanediol, polymer with
1,3-diisocyanatomethylbenzene and .alpha.-hydro-
.omega.-hydroxypoly[oxy(dimethylsilylene)], block

Me
|
[ HO(CH2)4OH . H-(O-Si-)n-OH . TDI ]
| x
Me

MF ((C9H6N2O2 . C4H10O2 . (C2H6OSi)nH2O)x

CA File: Siloxanes and Silicones
(polyurethane-, block)

Urethane polymers
(siloxane-, block)
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Example 2: A block siloxane-polyester from Me2SiCl2-Ph2SiCl2
hydrolytic siloxane, 1,4-butanediol, and adipic acid.

Registry File: Hexanedioic acid, polymer with 1,4-butanediol and
dichlorodimethylsilane hydrolytic polymer with
dichlorodiphenylsilane, block

Me Ph
| |
[HO2C(CH2)4CO2H . HO(CH2)4OH . (Cl-Si-Cl . Cl-Si-Cl . H2O)x]x
| |
Me Ph

MF ((C12H10Cl2Si . C2H6Cl2Si . H2O)x . C6H10O4 . C4H10O2)x

CA File: Siloxanes and Silicones
(polyester-, block)

Polyesters
(siloxane-, block)

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Example 3: A siloxane-polyester from HO(-Me2SiO-)x(-Ph2SiO-)yH,
1,4-butanediol, and adipic acid.

Registry File: Hexanedioic acid, polymer with 1,4-butanediol,
dimethylsilanediol and diphenylsilanediol, block
(Based on assumed monomers for the siloxane component)

Me Ph
| |
[HO2C(CH2)4CO2H . HO(CH2)4OH . HO-Si-OH . HO-Si-OH]x
| |
Me Ph

MF (C12H12O2Si . C6H10O4 . C4H10O2 . C2H8O2Si )x

CA File: Siloxanes and Silicones
(polyester-, block)

Polyesters
(siloxane-, block)

9. Trade Names

Trade names for siloxanes and silsesquioxanes are cross-referred to the SRU when such can be registered. When the SRU is not registrable, cross-references are written to the controlled-term heading SILOXANES AND SILICONES or SILSESQUIOXANES with appropriate substituent descriptions in the text modification.

10. Silicone Rubbers

Silicone rubbers are indexed at the modified controlled-term heading RUBBER, SILICONE. Additional entries are made for the polymer based on actual or assumed (hydroxysilane) monomers and for the SRU whenever possible. No entries are made at the controlled-term heading SILOXANES AND SILICONES for rubbers.

Text modifications at the modified controlled-term heading RUBBER, SILICONE typically contain a description of substituents on the siloxane backbone. Trade names for silicone rubbers are cross-referred to the modified heading RUBBER, SILICONE with substituent information placed in the text modification at that heading.

Example 1: Di-Me silicone rubber

Registry File: Poly[oxy(dimethylsilylene)] [9016-00-6]

Silanediol, dimethyl-, homopolymer [31900-57-9]
(polymer based on assumed monomer)

(The term "rubber" will appear in the text modification
at both RNs in the CA File.)

CA File: Rubber, silicone
(di-Me)