Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-03-05
2001-02-20
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S850000, C524S853000, C524S849000
Reexamination Certificate
active
06191215
ABSTRACT:
Process for the preparation of pulverulent polymers by polymerization in supercritical carbon dioxide in the presence of polyoxyalkylene-polysiloxane copolymers
The present invention relates to a process for the preparation of pulverulent polymers by polymerization of ethylenically unsaturated monomers (a) supercritical carbon dioxide as inert diluent.
Supercritical carbon dioxide is a highly suitable solvent or inert diluent for a large number of polymerization reactions. Because of its favorable cost, nonflammability and good compatibility with the environment, supercritical carbon dioxide has many advantages over conventional organic solvents. In addition, supercritical carbon dioxide has low viscosity and surface tension and thus offers the advantages of a more favorable mass transfer, and, moreover, is easier to remove from the polymerization product than is, for example, water. Despite all these advantages, its use is frequently restricted due to its low solvency for polar substances, In order to overcome this disadvantage, amphiphilic compounds are generally added to the polymerization medium which have a CO
2
-compatible moiety and a suitable polar content.
US-A 5 312 882 and US-A 5 506 317 describe heterophase polymerizations of hydrophobic monomers in supercritical carbon dioxide in the presence of fluorine- or silicone-containing stabilizers.
WO 96/37535 discloses the preparation of poly(phenyl oxides) by polymerization in supercritical carbon dioxide in the presence of fluorine- or silicone-containing stabilizers.
However, these stabilizers known to date are, in the case of the fluorine-containing compounds, costly, are sometimes not approved for desired fields of use, are difficult to obtain experimentally, and are disadvantageous with respect to environmental compatibility.
EP-A 633 018 discloses the use of polyoxyalkylenepolydimethylsiloxanes as additive for the stabilization of cosmetic emulsions.
It is an object of the present invention to find stabilizers which help to overcome said disadvantages.
We have found that this object is achieved by a process for the preparation of pulverulent polymers by polymerization of ethylenically unsaturated monomers (a) in supercritical carbon dioxide as inert diluent, which comprises carrying out the polymerization in the presence of polyoxyalkylene-polysiloxane copolymers.
According to the invention, suitable stabilizers are polyoxyalkylene-polysiloxane copolymers, which can either be graft or block copolymers.
Suitable copolymers of the graft type have a structure of the formula I,
suitable copolymers of the block type a structure of the formula II
where R
1
and R
2
independently of one another are a hydrogen atom, a C
1
-C
6
-alkyl radical or a branched or unbranched poly(dimethylsiloxane) radical having up to 40 siloxane units, R
3
is a polyoxyalkylene radical having from 3 to 20 oxyalkylene units, and m, n, x, and y independently of one another are an integer from 1 to 1000.
Preferred radicals R
1
and R
2
are C
1
-C
5
-alkyl radicals. R
3
is preferably a polyoxyethylene radical. The end group of R
3
can be a hydroxyl group, an alkyl ether group having from 1 to 5 carbon atoms or a trimethylsiloxy group.
Preferred values for m n, x and y are from 10 to 350.
The preparation of such polyoxyalkylene-polysiloxane copolymers by hydrosilylation in the presence of a platinum-containing catalyst is known per se (cf. J. B. Plumb and J. H. Atherton, Block Copolymers, publisher; D. C. Allport and W. H. Janes, Applied Science Publishers Ltd., London, 1973, page 305-325).
They can be obtained, for example, by reaction of corresponding poly(dimethylsiloxane-methylhydrosiloxanes) with monoallylpolyalkylene oxides in the presence of a platinum catalyst, where appropriate also by additional reaction with a vinylpoly(dimethylsiloxane) to obtain branched structures.
Examples of suitable platinum-containing catalysts are: platinum-divinyltetramethyldisiloxane, platinum/cyclovinylmethylsiloxane complex (2-2.5% Pt concentration in xylene), platinum/carbonyl complex (3-3.5% in vinyl-terminated polydimethylsiloxane) or H
2
(PtCl
6
)*6H
2
O (hexachloroplatinic(IV) acid hexahydrate.
The polyoxyalkylene-polysiloxane copolymers generally have molecular weights in the range of 500-30,000 g/mol.
Suitable reactive methylhydrosiloxanes are, in particular,
The polyoxyalkylene-polysilicane copolymers generally have molecular weights in the range of 500-30,000 g/mol.
Suitable reactive methylhydrosiloxanes are, in particular, hydrogen-terminated poly(dimethylsiloxanes) with a molecular weight of 10
2
-2.5×10
4
g/mol, and poly(dimethylsiloxanemethylhydrosilanes) with a molecular weight of 10
2
-2.5×10
4
g/mol and a methylhydrosiloxane content of from 0.5 to 30 mol %. Suitable alkyl radicals R
1
and R
2
are methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, isopentyl, or hexyl radicals. Branched or unbranched poly(dimethysiloxane) radicals R
1
and R
2
are introduced via reactive vinyl precursors; suitable precursors are, in particular, vinyldiethylmethylsilane, vinyldimethyl ethoxysilane, vinylethyldimethylsilane, vinyltrimethylsilane, vinyltriethyltilane, (N-vinylformamido)trimethylsilane, vinylmethylbis(trimethylsiloxy)silane, vinylmethyldiacetoxysilane, vinylmethyldiethoxysilane, vinylmethyldimethoxysilane, vinylmethylsilacyclopentane, vinyloxytrimethylsilane, vinylpentamethyldisiloxane, vinyltriacetoxysilane, vinyltri-t-butoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltriisopropoxysilane, vinyltrimethoxysilane, vinyltris(2-methoxyethoxy)silane, vinyltris(trimethylsiloxy)silane and vinyl-terminated poly(dimethylsiloxanes) with molecular weights of up to 3000 g/mol.
Suitable reactive precursors for introducing the branched or unbranched poly(oxyalkylene) radical R
3
into the copolymer are monoallylpolyoxyalkylene ethers with a molecular weight of from 100 to 1000 g/mol, preferably from 300 to 600 g/mol. These can carry, as end groups, a hydroxyl group, a C
1
-C
5
-alkoxy group or a trimethylsiloxy group, methoxy and ethoxy groups being preferred. said precursors are commercially available.
According to the invention, suitable polyoxyalkylenepolysiloxane copolymers are, for example:
(
x+y
)=6
x=
1, 2, 3,
m=
200-250
n=7to 8 (p=3, 7, 12), m=200-250
The polymerization is carried out under pressure in supercritical carbon dioxide as inert diluent. The properties of carbon dioxide in the liquid and in the supercritical state have been reported by J. A. Hyatt, J. Org. Chem. 49, 5097-5101 (1984). According to this, the critical point of carbon dioxide lies at about 31° C. and 73 bar. The polymerization is preferably carried out under pressure in supercritical carbon dioxide at temperatures above 31° C., the critical temperature of the carbon dioxide. The upper limit for the preparation of the polymers is regarded as the temperature which is 10° C. above the start of the softening range of the particular polymer being formed. The upper value for this temperature limit is 150° C. for most polymers. The polymerization is advantageously carried out in the temperature range from 30 to 130° C. The reaction temperature does not have to be kept contant; it is also possible to use a staged or ramped temperature profile. At the start of the reaction, temperatures in the range from 31 to 100° C. are advisable. The pressures are above 73 bar, preferably in the range from 80 to 400 bar, particularly preferably from 120 to 350 bar.
The process according to the invention is preferably carried out by firstly, in the reaction chamber, introducing carbon dioxide in the solid, liquid or gaseous state into pressurized apparatuses which are customary per se, then increasing the pressure to values above 73 bar and the temperature to values above 31° C. to covert the carbon dioxide into the supercritical state, then adjusting the reaction temperature and finally metering in the substances. The feed substances such as monomers, free-radical initiators, crosslinkers and, if appropriate
Beckham Eric
Fink Ralf
Hildebrandt Volker
BASF - Aktiengesellschaft
Keil & Weinkauf
Moore Margaret G.
LandOfFree
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