Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2002-10-11
2004-06-22
O'Sullivan, Peter (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C524S783000, C524S779000, C524S786000, C524S789000, C528S017000, C528S018000, C528S025000, C528S029000, C556S456000
Reexamination Certificate
active
06753438
ABSTRACT:
This invention is concerned with the chemical reaction of compounds having silicon bonded hydroxy or alkoxy groups by way of condensation reactions.
It is well known that chain extension and crosslinking reactions of silicon containing compounds may be achieved readily by way of condensation of silicon bonded hydroxy, alkoxy or other condensable groups present in the compound or formed therein, for example, during the course of condensation. These reactions may be, for example, according to the schemes:
2~SiR
2
OH→~SiR
2
OSiR
2
O~+H
2
O, or
~SiR
2
OH+ROSiR
2
OR→~SiR
2
OSiR
2
OR+ROH where R represents a substituted or unsubstituted, saturated or unsaturated hydrocarbon group.
Such reactions are employed in commerce especially in the manufacture of polydiorganosiloxanes of elevated molecular weights and in the formulation of a variety of silicone compounds employed in one part or multi part form for a wide range of uses in which the compound is required to cure in situ to a crosslinked condition. The polymerisation of silanol containing oligomers HO (SiMe
2
O)
n
H (where Me represents a methyl group CH
3
and n has a value of, for example, from about 4 to about 40) to form silicone polymers of elevated molecular weight (i.e. n has a value in excess of 1,000) by condensation is an extremely important part of the process for manufacture of silicone polymer materials having viscosities varying from those of fluids to those of gums. It is well known that this chain extension process may be carried out batchwise or continuously. Typically the reaction is conducted in the presence of one or more catalyst materials.
Various acidic and basic materials are known for use as catalysts for reaction of organosilicon materials via silanol condensation reaction, for example potassium hydroxide, ammonium hydroxide, barium hydroxide, acid clays, sulphonic acids, and phosphazene bases. However, these catalysts tend to catalyse other reactions simultaneously in addition to condensation reactions and one consequence can be the presence of significant proportions of cyclic siloxanes in the product. Also, catalysts are required to perform consistently and should be capable of removal (along with other undesirable residues) from the product, and those for use in continuous production processes are required to perform rapidly. One type of material proposed for use in the manufacture of silicones of elevated molecular weight is a phosponitrile chloride. Although this material has a number of advantages as a catalyst for the polymerisation of organosilicon materials, it is produced and used in chlorinated solvents which are regarded as potentially environmentally hazardous and thus require special handling. It is also rather difficult to neutralise consistently in the polymer production. Furthermore the phosphonitrile chloride is susceptible to hydrolysis and on prolonged exposure to water loses catalytic activity.
Thus, despite the many proposals for catalysis materials for such condensation reactions there remains a desire to provide a material which can serve as an effective catalyst, which can be prepared by a simple process and which does not leave, within the bulk of the reaction product, residues which are difficult to neutralise or remove.
Surprisingly we have now found that condensation of compounds having silicon bonded hydroxy or alkoxy groups may be achieved in presence of a catalytic amount of one or more materials providing a source of anions comprising at least one quadri-substituted boron atom and protons capable of interaction with at least one silanol group.
The present invention provides in one of its aspects a process for the condensation of a compound having a silicon bonded hydroxy or alkoxy group in the presence of a catalytic amount of one or more materials providing in the reaction mixture an anion comprising at least one quadri-substituted boron atom and protons capable of interaction with at least one of said silicon bonded hydroxy or alkoxy groups.
In a process according to the invention, it is important that the boron containing anion does not itself form a covalent bond directly to a silicon atom and that it does not decompose or rearrange to produce an anion which forms a covalent bond directly to a silicon atom. Suitable materials include those incorporating one or more boron atoms disposed within a grouping and several, for example ten or more, halogen atoms connected with each boron atom. The halogen atoms in such compound may be connected to boron atoms by linkages incorporating at least one carbon atom. The halogen atoms are preferably selected from fluorine, chlorine and bromine, the most preferred being fluorine. Preferred anions incorporate one or more atoms of boron having four organic substitutes thereon the most preferred being quadri-substituted borates. The organic substituents are suitably hydrocarbon groups. Three and preferably four of these hydrocarbon groups are preferably aromatic groups, and are preferably highly halogenated. Preferred halogenated hydrocarbons are pentafluorinated phenyl groups and his (trifluoromethyl) phenyl groups and preferred materials have four such groups bonded to each boron atom. One operative material is the tetrakis (pentafluoro phenyl) borate anion (otherwise herein referred to as the perfluorinated aryl borate ion) and the material is preferably employed as the acid of this anion namely H
+
{(C
6
F
5
)
4
B}
−
. Other operative materials include anions having two quadri-substituted boron atoms for example, di-perfluoroinated aryl borate ions eg H
+
{B(C
6
F
5
)
3
CNB(C
6
F
5
)
3
}
−
. The preferred materials can be readily prepared from commercially available compounds by simple ion exchange techniques in innocuous solvents, for example, water or alcohol. We prefer to prepare the acids prior to introducing catalytic amounts of them to the reaction mixture.
Other suitable boron-containing anions for use in the process of the present invention include carboranes, for example of the formula: {CB
9
H
10
}
−
, {CB
9
X
5
H
5
}
−
, {CB
11
H
12
}
−
, and {CB
11
X
6
H
6
}
−
, wherein X represents fluorine, chlorine, bromine or iodine. Carboranes may contain boron atoms which are more highly substituted than quadri-substituted, eg penta-substituted and hexa-substituted, and for the sake of clarity, “quadri-substituted” where used herein is intended to include those anions containing quadri-substituted and higher substituted boron atoms.
In a process according to the invention, one may employ any suitable compound having silicon bonded hydroxy or alkoxy groups. Preferred materials are silanes and siloxane compounds having at least one unit according to the general formula:
R
o
a
R
1
b
R
2
c
SiO
(4−(a+b+c)/2)
(i)
in which each R
o
represents a hydroxy, alkoxy, alkoxyalkoxy or hydrocarbonoxy group having up to 10 carbon atoms, each R
1
represents a hydrogen atom or a monovalent substituted or unsubstituted hydrocarbon group, each R
2
represents a divalent substituted or unsubstituted alkylene, or oxyalkylene group which is linked for example to another unit of formula (i) or an atom of a polymeric material, as referred to below a has the value of 1, 2, 3, or 4, b has a value of 0, 1, 2 or 3, c has a value of 0, 1, 2 or three and a+b+c has the value of 1, 2, 3 or 4. Suitable groups R
o
include, for example, hydroxy, methoxy, ethoxy, butoxy, phenoxy, and methoxyethoxy. Suitable groups R
1
include, for example, hydrogen, alkyl groups for example methyl, ethyl, propyl, isobutyl, hexyl, dodecyl or octadecyl, alkenyl for example, vinyl, allyl, butenyl, hexenyl or decenyl, alkynyl for example propargyl, aryl for example phenyl, aralkyl for example tolyl or xylyl, substituted hydrocarbon groups for example trifluoropropyl, chloropropyl or chlorophenyl. Suitable groups R
2
include for example, —(CH
2
)
n
— where n has a value of 1, 2, 3 or more and —(OCH
2
CHR
3
)
m
Habimana Jean De La Croi
Leadey Stuart
Taylor Richard Gregory
Dow Corning Corporation
McKellar Robert L.
McKellar Stevens, PLLC
O'Sullivan Peter
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