Organopolysiloxane materials which can be cross-linked by...

Details Organopolysiloxane materials which can be cross-linked by... Organopolysiloxane materials which can be cross-linked by...

2000-07-18

2003-03-11

Shaver, Paul F. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Silicon containing

C556S453000, C528S012000, C528S023000

Reexamination Certificate

active

06531621

ABSTRACT:

The invention relates to the preparation of alkoxy-terminated organopolysiloxane and to the use of this organopolysiloxane as a constituent of alkoxy RTV1 compositions.
For the purposes of the present invention, the term organopolysiloxanes is intended to include dimeric, oligomeric and polymeric siloxanes.
Organopolysiloxane compositions which can be stored while moisture is excluded and which crosslink when exposed to moisture at room temperature, with elimination of alcohols, are known as alkoxy RTV1 compositions and have been known for a long time. They essentially consist of organyloxy-terminated organopolysiloxane and, as other constituents, crosslinking agents having at least three hydrolyzable groups, catalyst and, if desired, additives. The advantage of these alkoxy RTV1 systems is that the alcohols released as cleavage products during the crosslinking are odorless, neutral and not harmful to the environment.
Alkoxy-terminated organopolysiloxane is prepared by reacting HO-terminated organopolysiloxane with alkoxysilanes. This is described in U.S. Pat. No. 4,942,211, for example. A disadvantage of this process is that the reaction requires several hours at room temperature. At elevated temperature although the reaction time is shortened it is still long enough for there to be some waiting time before the alkoxy-terminated organopolysiloxane formed can be used with other constituents to prepare alkoxy RTV1 compositions.
It is known that reactions of HO-terminated organopolysiloxane with alkoxysilanes can be accelerated by various catalysts. For example EP-A-763 557 carries out the reaction in the presence of acid dialkyl phosphoric esters. The dialkyl phosphates have to be deactivated by bases after their reaction, since otherwise the alkoxy-terminated organopolysiloxanes become depolymerized and loose their crosslinking capability.
The object on which the invention is based is to find a very simple way of preparing alkoxy-terminated organopolysiloxane for alkoxy RTV1 compositions.
The invention provides a process for preparing alkoxy-terminated organopolysiloxane, in which
(A) HO-terminated organopolysiloxane is reacted with
(B) alkoxysilane which has at least three alkoxy groups and/or its partial hydrolysates, in the presence of
(C) acid phosphoric ester of the general formula (I)
(HO)
a
OP(—O—[(CR
1
2
)
b
—O]
c
(CR
2
)
d
—L—M)
(3−a)
where
a is 1 or 2,
R
1
and R
2
are a hydrogen radical, methyl radical or hydroxyl radical,
b and d are 2 or 3,
c is an integer from 2 to 15,
L is a radical selected from the class consisting of —O—, —COO—, —OOC—, —CONR
3
—, —NR
4
CO— and —CO—,
R
3
and R
4
are a hydrogen radical or C
1
-C
10
-alkyl radical, and
M is a monovalent, unsubstituted or hydroxyl-, fluorine-, chlorine-, bromine-, C
1
-C
10
-alkoxyalkyl- or cyano-substituted C
1
-C
20
-hydrocarbon radical, with the proviso that on any carbon atom only one radical R
1
and R
2
may be a hydroxyl radical.
The process runs at temperatures as low as room temperature with an extremely high rate of reaction and selectively, and therefore immediately after mixing components (A), (B) and (C), the alkoxy-terminated organopolysiloxane formed can be used as an alkoxy RTV1 composition, if desired after admixing other constituents. There is no need to check whether the reaction has run to completion.
Another advantage of this process is that no side-reactions occur and, for example, no formation of T units or Q units is observed on a linear organopolysiloxane.
The acid phosphoric esters (C) do not have to be deactivated immediately after the reaction.
c is preferably an integer from 2 to 10, in particular 2, 3, 4 or 5. L is preferably an —O— radical. M is preferably an unsubstituted or C
1
-C
10
-alkoxyalkyl-substituted C
1
-C
20
-hydrocarbon radical, in particular an unsubstituted C
5
-C
18
-hydrocarbon radical. R
1
and R
2
are preferably a hydrogen radical. b and d are preferably 2.
The HO-terminated organopolysiloxanes (A) used are preferably linear &agr;, &ohgr;-dihydroxypoly(diorganosiloxanes) of the general formula (II)
HO—[(R
2
SiO]
m
—H  (II),
where
R is a monovalent, unsubstituted or fluorine-, chlorine-, bromo-C
1
-C
4
-alkoxyalkyl- or cyano- substituted C
1
-C
8
-hydrocarbon radical, and
m has a value which corresponds to a viscosity of the HO-terminated organopolysiloxane (A) of from 0.05 to 1000 Pa.s.
Examples of hydrocarbon radicals R are linear and cyclic, saturated and unsaturated; alkyl radicals, such as the methyl radical, aryl radicals, such as the phenyl radical, alkaryl radicals, such as tolyl radicals, and aralkyl radicals, such as the benzyl radical.
Preferred radicals R are unsubstituted hydrocarbon radicals having from 1 to 6 carbon atoms, particularly preferably the methyl radical.
The organopolysiloxanes (A) preferably have a viscosity of from 100 to 700,000 mPa.s, in particular from 20,000 to 350,000 mPa.s, measured in each case at 23° C.
The alkoxysilanes (B) preferably have the general formula (III)
R
5
&mgr;
Si (OR
6
)
4−&mgr;
  (III),
where
R
5
and R
6
are monovalent, unsubstituted or fluorine-, chlorine-, bromine-, C
1
-C
4
-alkoxyalkyl- or cyano-substituted C
1
-C
13
-hydrocarbon radicals, and
&mgr; is 0 or 1.
The partial hydrolysates of alkoxysilane (B) have been produced by hydrolyzing and condensing in particular from 2 to 4 alkoxysilanes. Examples of partial hydrolysates (B) are hexamethoxydisiloxane and hexa-ethoxydisiloxane.
Each of R
5
and R
6
is preferably an unsubstituted C
1
-C
6
-hydrocarbon radical, in particular a methyl, ethyl or propyl radical.
The acid phosphoric esters (C) of the general formula (I) are storage-stabilizers for the alkoxy RTV1 compositions prepared from the alkoxy-terminated organopolysiloxane. In particular, the skin formation times of the alkoxy RTV1 compositions remain virtually constant and stable, and discoloration is suppressed.
In the general formulae (I) to (III), all of the radicals R and R
1
to R
8
, and all of the indices a, b, c, d, e, m and &mgr;, are identical or different, independently of one another.
In all of the formulae the silicon atom is tetravalent. For example, n+o is not more than 4.
The amounts of the acid phosphoric esters (C) used, based on 500 parts by weight of the HO-terminated organopolysiloxanes (A) are from 0.1 to 50 parts by weight, in particular from 2 to 20 parts by weight.
The alkoxysilanes (B) are preferably added in excess to the HO-terminated organopolysiloxanes (A) in terms of the stoichiometric ratios. In order to permit the reaction of the HO-terminated organopolysiloxanes (A) with alkoxysilanes (B) to run as far as possible toward completion, use may preferably be made of from 10 to 60 parts by weight, in particular from 20 to 50 parts by weight, of the alkoxysilanes (B) per 500 parts by weight of the HO-terminated organopolysiloxanes (A). The excess of alkoxysilanes (B) not consumed during the reaction is not disadvantageous in the organyloxy-terminated organo-polysiloxane and in the alkoxy RTV1 compositions, and may therefore remain in the product of the reaction. An excess of alkoxysilanes (B) acts as crosslinking component in the alkoxy RTV1 compositions.
The reaction preferably takes place at temperatures of from +20 to +50° C., in particular at room temperature. Depending on the alkoxysilane (B) used, the reaction time is from 1 to 10 minutes.
The rate of the reaction depends firstly on the reactivity of the alkoxysilane (B) used and secondly on the acid phosphoric ester (C).
At room temperature the particularly preferred duration of the reaction is from 2 to 5 min, and this is specifically an advantage for preparing RTV1 compositions by the one-pot process.
The invention also relates to alkoxy RTV1 compositions which comprise the reaction product prepared by the abovementioned process, in which a substantial constituent is alkoxy-terminated organopolysiloxane.
In addition to the abovementioned components, the alkoxy RTV1 compositions may comprise other components known per se.
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