Polymerization of siloxanes

Details Polymerization of siloxanes Polymerization of siloxanes

1999-12-09

2002-02-12

Dawson, Robert (Department: 1712)

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

Synthetic resins

From silicon reactant having at least one...

C528S021000, C528S034000, C528S037000, C528S038000

Reexamination Certificate

active

06346593

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the polymerisation of siloxanes catalyzed by certain phosphazene bases, and in particular to the formation of polymeric siloxanes having amino-functionality.
BACKGROUND OF THE INVENTION
In EP0860461-A, there is described a process for the ring-opening polymerization of cyclosiloxanes, which comprises contacting a cyclosiloxane with 1 to 500 ppm of a phosphazene base, by weight of cyclosiloxane, in the presence of water. In GB 2311994, there is described a method of effecting polycondensation which comprises contacting at a temperature of from 0 to 200° C. and a pressure up to 350 torr, a silanol-containing organosiloxane with an amount of a peralkylated phosphazene base which is effective for polycondensation of said organosiloxane. The preferred peralkylated phosphazene base has the formula
The prior art is useful for the manufacture of higher molecular weight polysiloxane materials with hydrocarbon or hydroxyl substituents. There is a need for making siloxane polymers which have other functionalities, and in particular amine functionality. It is particularly difficult to make amino-functional siloxanes by polymerization. An existing method uses equilibration of cyclic siloxanes with aminofunctional silanes or siloxanes in the presence of strong base catalysts, such as potassium hydroxide or potassium silanolate, described in EP 575972. Alternatively, a condensation reaction is used starting from silanol-functional siloxane polymers in conjunction with amino-functional organosilicon compounds, e.g. silanes. This method is useful and effective in many ways, but slow, and often requires a complex catalyst system. Many catalytic systems are affected by the presence of amines, and are thus not suitable as a solution to the problem.
SUMMARY OF THE INVENTION
This invention is a polymerization process comprising mixing a siloxane polymer with an organosilicon compound having at least one silicon-bonded group R
N
, which is a substituent comprising at least one amine group, with a phosphazene base catalyst and allowing the siloxane and organosilicon compound to polymerize to form amino-functional polyorganosiloxane polymers.
We have surprisingly found that phosphazene base materials are effective catalysts for polymerization of siloxanes in order to provide amino-functional siloxanes. They are furthermore found to be effective, whether they are used to make the amino-functional siloxanes via condensation or equilibration reaction, or even, if desired, by a combination of both reaction types.
DETAILED DESCRIPTION OF THE INVENTION
According to a first aspect of the invention there is provided a polymerization process comprising mixing certain siloxanes and organosilicon compounds having at least one silicon-bonded group R
N
, which is a substituent comprising at least one amine group, with one or more phosphazene base catalysts and allowing the siloxanes and organosilicon compounds to polymerize to form amino-functional polyorganosiloxane polymers.
Phosphazene bases themselves are known to be extremely strong bases. Numerous phosphazene bases, some of which are ionic phosphazene bases and routes for their synthesis have been described in the literature, for example in Schwesinger et al., Liebigs Ann. 1996, 1055-1081.
Phosphazene bases are found to be a very powerful catalyst for polymerization of siloxane materials, and can therefore be present in a relatively low proportion, for example from 1 to 2000 ppm, preferably 2 to 1000 ppm by weight, based on the weight of siloxanes. The proportion of catalyst actually used will be selected depending on the speed of polymerization that is sought or on the size of polymer required.
A proportion of water may be present in the reaction, especially where the phosphazene used is a non-ionic phosphazene. Where this is the case, it is preferably at least 0.5, more preferably from 0.5-10 mols per mol of the ionic phosphazene base, most preferably from 1 to 10 mols per mol of ionic phosphazene base. It is possible to allow higher proportions of water, and this can have the benefit of enabling greater control over the polymerization reaction, as described in more detail below.
In principle, any phosphazene base is suitable for use in the present invention. Phosphazene bases generally include the following core structure P═N—P═N, in which free N valencies are linked to hydrogen, hydrocarbon, —P═N or ═P—N, and free P valencies are linked to —N or ═N. Some ionic phosphazene bases, for example 1-tert-Butyl-4,4,4-tris(dimethylamino)-2,2-bis{tris(dimethylamino)-phosphoranylidenamino}-2&lgr;
5
, 4&lgr;
5
-catenadi(phosphazene)}, are commercially available e.g. from Fluka Chemie AG, Switzerland. The ionic phosphazene bases preferably have at least 3 P-atoms. Some preferred phosphazene bases are of the following general formulae:
((R
1
2
N)
3
P═N—)
x
(R
1
2
N)
3−x
P═NR
2
{((R
1
2
N)
3
P═N—)
x
(R
1
2
N)
3−x
P—N(H)R
2
}
+
{A
−
}
{((R
1
2
N)
3
P═N—)
y
(R
1
2
N)
4−y
P}
+
{A}
−
{(R
1
2
N)
3
P═N—(P(NR
1
2
)
2
═N)
n
—P
+
(NR
1
2
)
3
}{A
−
}
in which R
1
, which may be the same or different in each position, is hydrogen or an optionally substituted hydrocarbon group, preferably a C
1
-C
4
alkyl group, or in which two R
1
groups bonded to the same N atom may be linked to complete a heterocyclic ring, preferably a 5- or 6-membered ring; R
2
is hydrogen or an optionally substituted hydrocarbon group, preferably a C
1
-C
20
alkyl group, more preferably a C
1
-C
10
alkyl group; x is 1, 2 or 3, preferably 2 or 3; y is 1, 2, 3 or 4, preferably 2, 3 or 4; n is an integer with a value of from 1 to 10.and A is an anion, preferably fluoride, hydroxide, silanolate, alkoxide, carbonate or bicarbonate.
Particularly suitable compounds are those where R
1
is methyl, R
2
is tertiary butyl or tertiary octyl, x is 3, y is 4, n is 1 to 4 and A is fluoride or hydroxide. Suitable phosphazene base catalysts are commercially available, or can be made by a process disclosed by Schwesinger et al, as indicated above. The compounds of the formula {(R
1
2
N)
3
P═N—(P(NR
1
2
)
2
═N)
z
—P
+
(NR
1
2
)
3
} {A}
−
may be made by a method which comprises reacting a linear phosphonitrile halide compound, preferably chloride, with a compound selected from a secondary amine, a metal amide and a quaternary ammonium halide to form an aminated phosphazene material, followed by an ion exchange reaction replacing the anion with a nucleophile. Phosphonitrile halide compounds and methods of making them are well known in the art; for example, one particularly useful method includes the reaction of PCl
5
with NH
4
Cl in the presence of a suitable solvent. Secondary amines are the preferred reagent for reaction with the phosphonitrile halide, and a suitable secondary amine has the formula R
3
2
NH, wherein R
3
is a hydrocarbon group having up to 10 carbon atoms, or both R
3
groups form a heterocyclic group with the nitrogen atom, for example a pyrollidine group, a pyrrole group or a pyridine group. Preferably, R
3
is a lower alkyl group, more preferably a methyl group, or both R
3
groups form a pyrollidine ring. Suitable preferred secondary amines include dimethylamine, diethylamine, dipropylamine and pyrollidine. Preferably the reaction is carried out in the presence of a material which is able to capture the exchanged halides, e.g. an amine such as triethylamine. The resulting by-product (e.g. triethyl ammonium chloride) can then be removed from the reaction mixture, e.g. by filtration. The reaction may be carried out in the presence of a suitable solvent for the phosphonitrile chloride and linear phosphazene base. Suitable solvents include aromatic solvents such as toluene. The linear phosphazene material which is formed this way can be passed through an ion exchange reaction (preferably an ion exchange resin) whereby the anion is re

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