Organic compounds -- part of the class 532-570 series – Organic compounds – Sulfonic acids or salts thereof
Reexamination Certificate
2002-06-21
2003-10-14
Vollano, Jean F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Sulfonic acids or salts thereof
C562S030000, C562S113000, C568S001000, C568S009000
Reexamination Certificate
active
06632960
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to catalysts used in cationic polymerizations, and more particularly to diaryliodonium salt photo/thermal initiators, and a method for preparing them, wherein one of the aryl groups attached to the iodine moiety is substituted with a methyl group, and the other is substituted with an alkoxy group having a hydroxy group therein.
BACKGROUND OF THE INVENTION
Photoinitiated cationic polymerization is a rapid, energy efficient and pollution-free method for curing cationically polymerizable monomers, such as epoxy monomers. Particularly efficient photoinitiators include onium salts, such as diaryliodonium (1) salts:
Within the industry, diaryliodonium, as well as triarylsulfonium salts, have been the principal photoinitiators for cationic ultraviolet (UV) curing. Diaryliodonium salts having the structure shown in (1) have been described in the patent literature, notably in U.S. Pat. No. 4,683,317 to the instant inventor, J. V. Crivello, and colleague J. L. Lee. Therein, the subject salts are produced from the condensation of aryliodosotosylates and aryl ketones. The salts have been used as photoinitiators to effect deep section UV cures in photopolymerizable organic materials used for the encapsulation of electronic components.
J. V. Crivello also disclosed in U.S. Pat. No. 5,079,378 that the organic solubility of diaryliodonium salts could be increased by substituting at least one aryl radical with a long chain ester. In addition, J. V. Crivello reported in U.S. Pat. No. 5,073,643 hydroxyl-bearing diaryliodonium salts, wherein at least one aryl group is substituted with a long chain alkoxy group having a hydroxyl moiety attached at the 2-position of the alkoxy group. These salts were prepared by reacting a monoaryloxy-2-hydroxyalkane with [hydroxy(tosyloxy)iodo]benzene. The iodonium salts discussed in the aforementioned patents may also be used in thermally curable systems with or without a copper cocatalyst. An example of such a salt is [4-(2-hydroxy-1-tetradecyloxy)-phenyl] phenyliodonium hexafluoroantimonate, (commercially available from Polyset Corporation as PCX 2506 or from Sartomer as CD-1012), which is represented by the following structure (2):
EP 1088813 A2 discloses other modified diaryliodonium salts, which are reported to exhibit improved solubility in nonpolar media including organopolysiloxanes containing epoxy groups and n-alkanes. The salts contain a urethane moiety and are prepared by reacting hydroxyl-containing iodonium salts, such as the one depicted above, with reagents containing isocyanate groups. The reduced tendency of the resulting urethanes to crystallize makes them more soluble in nonpolar media, e.g., alkanes or siloxanes, than the hydroxyl-containing iodonium salt starting materials.
One disadvantage in using the aforementioned diaryliodonium salts is that often, benzene is produced when these catalysts are used in UV curing. Thus, benzene has the potential to vaporize or leach out of the polymer film. Because benzene is carcinogenic, the use of materials that may yield benzene is becoming more and more restricted. Therefore, it is desirable to find photo/thermal initiators which do not have this drawback, but which retain the solubility advantages associated with known onium salts.
A need, therefore, exists for catalytic onium salts, as well as a method of preparing them, wherein benzene is not a potential by-product when the photo/thermal intiatiors are employed for curing purposes. However, the solubility of such salts should not be compromised when compared with benzene-containing salts.
The present invention fulfills this need by providing hydroxyl-bearing iodonium salts, which do not contain benzene, and a method for preparing them from monoaryloxy-2-hydroxyalkanes and [hydroxy(tosyloxy)]iodoaryl salts. These hydroxyl-bearing iodonium salts are useful as photo/thermal initiators in cationic polymerization reactions, as well as for use in preparing the aforementioned urethanes. The present catalytic salts are also surprisingly more soluble than their benzene counterparts.
SUMMARY OF THE INVENTION
The present invention is directed to diaryliodonium salts and a method for preparing them in which one of the aryl groups bonded to the positively-charged iodine ion contains a methyl substituent, and the other one contains a hydroxyl-substituted alkoxy group. These salts are extremely useful as cationic photoinitiators, cationic thermal initiators, and as starting materials in the synthesis of urethane-containing iodonium salts. The present invention eliminates the problem of benzene leaching during polymerization and curing. The salts exhibit unexpectedly improved solubility in most organic solvents, as well as in nonpolar media, as compared with prior art salts prepared from iodobenzene. Another benefit of the present invention is that when the instant diaryliodonium salts contain the hexafluorophosphate anion, i.e., [PF
6
]
−
, the salts are surprisingly more soluble in nonpolar media than salts made from iodobenzene, which contain the hexafluoroantimonate anion. This is advantageous because antimony is generally considered to be a toxic metal, and its use is becoming quite limited. The present method also allows for preparation of the salts in good to excellent yield.
Briefly, in one aspect, the present invention includes diaryliodonium salts having the general formula (I)
wherein n is 0 or an integer from 1 to 25. The methyl substituent may be located at any position of the aryl ring, i.e., at the 2, 3, or 4-carbon relative to the carbon attached to the iodine atom, which is identified as the 1-carbon. The 2-, 3-, and 4-carbon positions are also known as ortho-, meta-, and para-, respectively, which may also be represented herein as o-, m-, and p-, respectively, as anyone of ordinary skill would know. A
−
is the anion of a complex metal halide or of a strong protonic acid. Anions, A
−
, derived from complex metal halide salts may be represented as [MX
m
]
−
, wherein M is boron, gallium, phosphorus, or antimony; X is halogen, and the value of m is 4 or 6. Alternatively, X may be C
6
F
5
when M is boron or gallium, and m is 4. Examples of such ions include [BF
4
]
−
, [PF
6
]
−
, [AsF
6
]
−
, [SbF
6
]
−
, [B(C
6
F
5
)
4
]
−
, and [Ga(C
6
F
5
)
4
]
−
. Anions from strong protonic acids include, e.g., [ClO
4
]
−
, [CF
3
SO
3
]
−
, [FSO
3
]
−
, [CH
3
SO
3
]
−
, and [C
4
F
9
SO
3
]
−
. It should be noted that a negatively charged moiety is conventionally indicated herein by a minus sign, either in a circle or without the circle. Each symbol is used interchangeably, and may be positioned as a superscript relative to the moiety. Similarly, a positively charged moiety is denoted by a plus symbol, with or without the circle.
In another aspect, the present invention provides a method for preparing an iodonium salt having the general formula (I) above. The method comprises reacting a compound having formula (II):
with a [hydroxy(tosyloxy)]iodoaryl salt (III) in the presence of a suitable solvent and a reagent providing the anion, A
−
. Structure (III) is represented as:
The substituent, R, is methyl (CH
3
) or hydrogen (H).
In yet another aspect, the present invention is a method for preparing a diaryliodonium salt in which one aryl group is substituted with a long chain alkoxy group possessing a hydroxyl moiety in the 2-position, and the other aryl group is substituted with a methyl group. The method comprises reacting a monoaryloxy-2-hydroxyalkane with a [hydroxy(tosyloxy)]iodoaryl salt of structure (III) above in the presence of a suitable solvent and providing an anion from a complex metal halide or a strong protonic acid, such as the anions mentioned above.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A general scheme
Crivello James V.
Feldmann-Krane Georg
Oestreich Sascha
Boden, Esq. Martha L.
Goldschmidt AG
Heslin Rothenberg Farley & & Mesiti P.C.
Vollano Jean F.
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