Siloxane copolymers containing alkenyl groups

Details Siloxane copolymers containing alkenyl groups Siloxane copolymers containing alkenyl groups

1999-11-23

2001-07-24

Dawson, Robert (Department: 1712)

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

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C528S015000, C528S031000, C528S032000, C528S025000

Reexamination Certificate

active

06265497

ABSTRACT:

TECHNICAL FIELD
The invention relates to alkenyl-containing siloxane copolymers and to a process for preparing them. The invention additionally relates to crosslinkable compositions which comprise an alkenyl-containing siloxane copolymer, an organopolysiloxane containing Si-bonded hydrogen atoms, and a catalyst, and to the use of said compositions to produce coatings which repel tacky substances.
BACKGROUND ART
U.S. Pat. No. 5,241,034 describes alkenyl-containing siloxane copolymers which are prepared by reacting an organic compound having two, three or four terminal aliphatic double bonds with organopolysiloxane having Si-bonded hydrogen atoms in the presence of a hydrosilylation catalyst. In the resulting copolymers the organopolysiloxane blocks are connected via hydrocarbon bridges.
In accordance with DE 41 23 423, branched alkenylsiloxane polymers are prepared which carry at least two alkenyl groups. The siloxanes used for the polyaddition reaction (final stage) have no more than two terminal SiH groups, whereas prior SiH-functional siloxanes used analogously, due to their branching, carried more than two SiH groups.
Alkenylsiloxanes are also discussed DE 196 466 42. In the latter, the alkenylsiloxanes acquire their branching by virtue of T units of the general structure RSiO
3/2
, incorporated by equilibration. The DE 195 484 74 discloses branched vinylsiloxanes which contain T units of the formula O
1/2
R
2
SiYRSiO. DE 195 221 44 describes branched SiH precursors having siloxane segments of not more than 6 silicon atoms, which are reacted with an excess of &agr;,&ohgr;-diene containing no siloxane units.
In DE 196 290 53 are disclosed polymers containing unsaturated end groups on siloxane segments which are attached directly to the organic branching unit. The preparation process involves complex hydrolytic steps and the use of halosilanes. DE 196 270 22 describes polymers which contain no organic branching units but instead customary siloxy structures as RSiO
3/2
and SiO
4/2
.
SUMMARY OF INVENTION
An object of the present invention was therefore to provide alkenyl-containing siloxane copolymers which can be prepared in a simple process which permits the starting components to be reacted at low temperatures, as far as possible with little or no external heating, in a short time. A further object is to thusly prepare synthesis products which crosslink rapidly with organopolysiloxanes containing Si-bonded hydrogen atoms in the presence of catalysts which promote the addition of Si-bonded hydrogen onto aliphatic double bonds. A yet further object was to provide alkenyl-containing siloxane copolymers bearing more than two, equally reactive terminal alkenyl groups per molecule, in each case at the end of a siloxane chain, and whose synthesis can be performed even without incorporation of T units and/or Q units of the formula RSiO
3/2
and SiO
4/2
, and in particular without the use of expensive &agr;,&ohgr;-dienes. A still further object was to provide crosslinkable compositions suitable for producing coatings which repel tacky substances. These and other objects are achieved by means of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention provides alkenyl-containing siloxane copolymers preparable by:
in a first step, preparing a hydrocarbon-siloxane copolymer containing Si-bonded hydrogen atoms, by reacting
a compound (1) having at least three aliphatic double bonds, of the general formula
R
2
(CR
3
═CH
2
)
x
 where
R
2
is a trivalent or tetravalent hydrocarbon radical having preferably 1 to 25 carbon atoms per radical,
R
3
is a hydrogen atom or an alkyl radical having preferably 1 to 6 carbon atoms per radical, and
x is 3 or 4; with
an organosiloxane (2) having terminal Si-bonded hydrogen atoms in the presence of catalyst (3) which promotes the addition of Si-bonded hydrogen onto aliphatic double bond,
the ratio employed of Si-bonded hydrogen in the organosiloxane (2) to aliphatic double bonds in organic compound (1) being from 1.3 to 10, preferably from 1.5 to 5,
in a second step reacting the hydrocarbon-siloxane copolymers containing Si-bonded hydrogen atoms prepared in said first step
with an &agr;,&ohgr;-dialkenylsiloxane polymer (4) in the presence of catalyst (3) which promotes the addition of Si-bonded hydrogen onto aliphatic double bond,
the ratio employed of aliphatic double bonds in the &agr;,&ohgr;-dialkenylsiloxane polymer (4) to Si-bonded hydrogen in the siloxane copolymers being from 1.2 to 10, preferably from 1.5 to 10,
and, if desired, in a third step
equilibrating the resulting alkenyl-containing siloxane copolymers with at least one organopolysiloxane (5) selected from the group consisting of linear organopolysiloxanes containing terminal triorganosiloxy groups, linear organopolysiloxanes containing terminal hydroxyl groups, branched organopolysiloxanes with or without hydroxyl groups, cyclic organopolysiloxanes, and copolymers of diorganosiloxane units and monoorganosiloxane units.
The invention additionally provides a process for preparing alkenyl-containing siloxane copolymers, comprising:
in a first step reacting in a first step, preparing a hydrocarbon-siloxane copolymer containing Si-bonded hydrogen atoms, by reacting
a compound (1) having at least three aliphatic double bonds, of the general formula
R
2
(CR
3
═CH
2
)
x
 where
R
2
is a trivalent or tetravalent hydrocarbon radical having preferably 1 to 25 carbon atoms per radical,
R
3
is a hydrogen atom or an alkyl radical having preferably 1 to 6 carbon atoms per radical, and
x is 3 or 4; with
an organosiloxane (2) having terminal Si-bonded hydrogen atoms in the presence of catalyst (3) which promotes the addition of Si-bonded hydrogen onto aliphatic double bond,
the ratio employed of Si-bonded hydrogen in the organosiloxane (2) to aliphatic double bonds in organic compound (1) being from 1.3 to 10, preferably from 1.5 to 5,
in a second step reacting the hydrocarbon-siloxane copolymers containing Si-bonded hydrogen atoms prepared in said first step
with an &agr;,&ohgr;-dialkenylsiloxane polymer (4) in the presence of catalyst (3) which promotes the addition of Si-bonded hydrogen onto aliphatic double bond,
the ratio employed of aliphatic double bonds in the &agr;,&ohgr;-dialkenylsiloxane polymer (4) to Si-bonded hydrogen in the siloxane copolymers being from 1.2 to 10, preferably from 1.5 to 10,
and, if desired, in a third step
equilibrating the resulting alkenyl-containing siloxane copolymers with at least one organopolysiloxane (5) selected from the group consisting of linear organopolysiloxanes containing terminal triorganosiloxy groups, linear organopolysiloxanes containing terminal hydroxyl groups, branched organopolysiloxanes with or without hydroxyl groups, cyclic organopolysiloxanes, and copolymers of diorganosiloxane units and monoorganosiloxane units.
In the alkenyl-containing siloxane copolymers of the invention the siloxane blocks are preferably connected to one another via hydrocarbon bridges, thus resulting in a hydrocarbon-siloxane block structure. The structure of alkenyl-containing siloxane copolymers is described in the above-cited U.S. Pat. No. 5,241,034, which is incorporated herein by reference.
The alkenyl-containing siloxane copolymers of the invention preferably have a viscosity of from 0.05 to 500,000 Pa·s at 25° C., more preferably from 0.1 to 100,000 Pa·s at 25° C., with particular preference from 0.2 to 10,000 Pa·s at 25° C.
In one preferred embodiment, the preparation of the siloxane copolymers of the invention takes place in a solvent, preferably a hydrocarbon having a boiling point below 150° C., and preferably with a concentration of 20-60% by weight siloxane. Higher or lower concentrations of siloxane are useful in the present invention as well.
The organosiloxanes (2) used in the first process step preferably contain two Si-bonded hydrogen atoms per molecule. In this first process step, it is possible to use a single organosiloxane (2), or different types of organosiloxanes (2). The organosiloxane (2) in the

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