Basic condensation catalyst systems for siloxanes

Details Basic condensation catalyst systems for siloxanes Basic condensation catalyst systems for siloxanes

2000-01-06

2001-11-06

Dawson, Robert (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From silicon reactant having at least one...

C528S014000

Reexamination Certificate

active

06313253

ABSTRACT:

TECHNICAL FIELD
The invention relates to a process for the condensation of compounds carrying silanol groups, in which basic catalyst systems are employed.
BACKGROUND ART
Basic condensation and equilibration catalysts are understood as meaning compounds which generate a pH of >7 in water, either directly, or due to their hydrolysis products, such as metal hydroxides or metal alkoxides of main groups I and II of the Periodic Table, or ammonium hydroxides, for example butyltrimethylammonium hydroxide (BTAH) or tetramethylammonium hydroxide (TMAH) and the like.
Basic condensation and equilibration catalysts are chiefly used in silicone chemistry for the preparation of siloxanes carrying amino groups and in resin synthesis, such as for the preparation of MQ resins. Basic catalysts are also used in the macroscopic gelling of alkoxysilanes for precursors of aero- and xerogels. Another field of use of “non-acid” condensation catalysts is vulcanization of silicone rubber compositions with organometallic compounds, for example tin compounds.
Disadvantages of the catalysts described above are that in addition to catalyzing the condensation reaction they also have always catalyzed the equilibration reaction, or that the rate of condensation is too low. Tin compounds are the only pure condensation catalysts, but these are not suitable for condensation of organosiloxanes to obtain higher molecular weights. Cryptates are disclosed in EP-B-23 187, and trioxoalkylamines in EP-A-180 527, as additives for optimizing the condensation properties of alkali metals and alkaline earth metals. The disadvantage of these catalyst systems is their high polarity and therefore their incompatibility with the siloxanes.
DISCLOSURE OF INVENTION
The object of the present invention is the development of a process for the polycondensation of organosiloxanes in which equilibration is not catalyzed and with which high molecular weights can be achieved.
BEST MODE FOR CARRYING OUT THE INVENTION
The invention relates to a process for the condensation of compounds which carry silanol groups and have at least one unit of the general formula (III)
A
c
E
d
SiO
(4-c-d)/2
  (III)
in which
A is a hydroxyl group,
E is an inert radical,
c is the value 1, 2, 3 or 4 and
d is the value 0, 1 or 2, with the proviso that c+d≦4, in which higher molecular weight organosiloxane compounds are prepared with a catalyst system comprising a catalyst chosen from basic alkali metal and alkaline earth metal compounds and a cocatalyst which is an at least bidentate chelating ligand and contains units of the general formula (I)
N-R
1
-N  (I)
 in which
R
1
is a divalent linear, cyclic and/or aromatic C
1
-to C
30
-hydrocarbon radical.
With the aid of these catalyst systems, compounds which carry silanol groups can undergo polycondensation to higher molecular weight compounds without being equilibrated.
The catalyst comprises an alkali metal compound or alkaline earth metal compound, or a mixture of alkali metal compound and alkaline earth metal compound, which achieves a pH of >7.0 in water and preferably corresponds to the general formula (II)
M
a
—(R
2
)b  (II),
in which
M is an alkali metal atom or alkaline earth metal atom,
R
2
is a monovalent group such as a hydroxyl, amine, C
1
-to C
18
-alkoxy or silicate group, a group which reacts with water to produce basic species, such as a hydrogen, amide or C
1
-to C
30
-hydrocarbon radical, or an oxidic metal compound, such that the compound M
a
—(R
2
)b, when added to water, renders the water alkaline,
a has the values 1 and 2, and in the case of alkali metals preferably the value 1, and
b has the values 1 and 2, with the proviso that in the case of alkali metals b can only assume the value 1.
Preferably, M is lithium, sodium, potassium, rubidium, cesium, calcium, strontium, or barium, in particular lithium or barium.
The C
1
-to C
18
-alkoxy group R
1
preferably is a methoxy or ethoxy radical. The C
1
-to C
30
-h-hydrocarbon radical R
2
is preferably a propyl or butyl radical. Preferred radicals R
1
are C
1
-to C
4
-hydrocarbon radicals, in particular the C
2
radical.
The cocatalysts are preferably linear or cyclic compounds which contain at least one and not more than 20 units of the general formula (I). Examples of these are 3,5-diazacyclohexane, 3,5,7-triazacyclooctane and ethylenediamine oligomers of the general formula H
2
N—(CH
2
CH
2
NH)
x
—H, wherein x can be an integer from 1 to 20.
The linear compounds which contain 1 to 5 units of the general formula (I) are particularly preferred here. Examples of these are ethylenediamine, diethylenetriamine, triethylenetetramine and tetraethylenepentamine.
Preferably, the radical E is a monovalent, optionally halogen- or cyano-substituted C
1
-to C
30
-hydrocarbon radical bonded via SiC, in particular a C
1
-to C
6
-hydrocarbon radical, such as the methyl, ethyl and phenyl radicals.
The compound carrying silanol groups can also first be formed during a reaction step, for example by the hydrolysis of a chlorosilane, and can then participate in the condensation reaction.


REFERENCES:
patent: 4138543 (1979-02-01), Bargain et al.
patent: 4308366 (1981-12-01), Millet
patent: 4362855 (1982-12-01), Millet et al.
patent: 4820673 (1989-04-01), Knopf et al.
patent: 0 023 187 B1 (1981-01-01), None
patent: 0 023 187 A1 (1981-01-01), None
patent: 0 039 299 A1 (1981-11-01), None
patent: 0 180 527 A1 (1986-05-01), None
patent: 2 398 079 (1977-07-01), None
Derwent Abstract Corresponding To EP-A 0 180 527 (AN 1986-120646).
Derwent Abstract Corresponding To FR 2 398 079 (AN 1979-320083).
International Search Report—Apr. 2, 2000.
Derwent Abstract corresponding to EP 0023187 (AN 1981-08219D).
Derwent Abstract corresponding to EP 0180527 (AN 1986-120646).

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