Iodonium salt photoinitiators containing urethane groups for...

Details Iodonium salt photoinitiators containing urethane groups for... Iodonium salt photoinitiators containing urethane groups for...

2000-09-19

2002-04-30

Berman, Susan W. (Department: 1711)

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

Synthetic resins

Compositions to be polymerized by wave energy wherein said...

C522S099000, C522S148000, C522S170000, C522S181000, C522S184000, C522S188000, C549S207000, C556S064000, C556S420000, C568S013000, C568S016000, C568S018000, C568S038000, C568S074000, C568S075000, C568S583000, C570S123000, C570S127000

Reexamination Certificate

active

06380277

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to iodonium salts of reduced crystallization tendency containing urethane groups, to a process for their preparation, and to their use for the radiation curing of cationically curing compositions.
2. Description of the Related Art
Cationic photopolymerization is a rapid, efficient and environment-friendly means of curing cationically polymerizable monomers. Particularly efficient photoinitiators are diaryliodonium salts (I) and triarylsulfonium salts (II).
Ar—I
+
—ArMX
n
−
  (I)
 MX
n
−
=BF
4
−
,PF
6
−
,AsF
6
−
,SbF
6
−
Diaryliodonium salts (I) in particular are known from the patent literature (DE-A-25 18 639, U.S. Pat. No. 4,279,717, EP-A-0 334 056, EP-B-0 618 919) and are used as photoinitiators for polymerizing cationically polymerizable substances. The cationically polymerizable substances, however, have little or no polarity, especially if the polymerizable groups are present in organopolysiloxanes. When adding these photoinitiators, therefore, it is a very common observation that, depending on the structure of the formulation, the miscibility and solubility of the photoinitiators is limited. For this reason, the aryl radicals of such onium salts are often substituted with alkyl chains in order to increase the solubility in organopolysiloxanes (U.S. Pat. No. 4,310,469 and U.S. Pat. No. 4,374,066).
In the case of hydroxyl-bearing iodonium salts as described in U.S. Pat. No. 5,073,643, the poor solubility in nonpolar media is attributed to the high crystallization tendency. The particular complexation characteristics of the hydroxyl-bearing iodonium salts of the general formula (III) result in a strong crystallization tendency of the compounds (A. Kunze, U. Müller, K. Tittes, J. P. Fouassier, F. Morlet-Savary, J. Photochemistry and Photobiology A: Chemistry, 110, 115-122 (1997)):
The two oxygen atoms in the molecule act as ligands for a second iodonium ion. This aggregation behavior promotes the formation of crystals.
In the preparation of these salts, the strong crystallization tendency is entirely desirable, since it means that the compounds can be recovered as powders in a high purity by simple recrystallization. In this way, they are easy and cost effective to prepare. Such iodonium salts are commercially available, for example, under the name CD-1012 from Sartomer.
The high crystallization tendency has an adverse effect, however, if the iodonium salts are to be dissolved in nonpolar media, such as organopolysiloxanes. In this case either they are insoluble or a solid precipitate forms after just a short time.
Because of their inhomogeneity, such coatings cure poorly on UV irradiation. However, it is also possible that, as a result of the inhomogeneity, massive surface defects (craters, wrinkles, specks, etc.) appear even during the application of a thin coat on a substrate.
OBJECTS OF THE INVENTION
It is an object of the present invention to modify hydroxyl-bearing iodonium salts in a particularly cost-effective and simple manner such that the crystallization tendency is greatly reduced and good compatibility, especially with organopolysiloxanes containing epoxy groups, is established, and the resulting compounds are stable to hydrolysis, so that reformation of hydroxyl-bearing iodonium salts in the course of storage is impossible.
SUMMARY OF THE INVENTION
These objects are achieved by means of iodonium salts of the general formula (IV)
[R
1
—I—R
2
]
+
X
−
  (IV)
where
I is iodine,
X
−
is an anion of a complex metal salt and/or of a strong acid,
R
1
is the radical
 in which
Ar is an aromatic hydrocarbon radical, preferably, having 6 to 14 carbon atoms per radical or is an aromatic hydrocarbon radical containing at least one oxygen and/or sulfur atom and, preferably, having 5 to 15 ring atoms per radical,
a is 1, 2 or 3,
b is 0, 1 or 2,
c is 0, 1 or 2,
D, E and F are each substituents of Ar,
D being a radical of the formula
 where
x is 0 or 1,
y is 0 or 1,
R
3
is a linear or branched divalent hydrocarbon radical, preferably, having 1 to 40 carbon atoms per radical, which can be interrupted, if desired, by at least one oxygen atom and/or at least one sulfur atom and/or at least one carboxyl group, R
4
is a monovalent linear, branched and/or cyclic alkyl, aryl, haloalkyl and/or haloaryl radical, preferably, having 1 to 40 carbon atoms, which can be interrupted, if desired, by at least one oxygen atom and/or at least one sulfur atom and/or at least one urethane group and/or ester group, and which can, if desired, contain hydrophobicizing substituents and/or at least one isocyanate group,
E is a radical of the formula
—O—R
5
F is a radical of the formula
—R
6
R
2
is a radical of the formula
 where
R
5
is a monovalent hydrocarbon radical, preferably having 1 to 18 carbon atoms per radical, which can be interrupted, if desired, by at least one oxygen atom,
R
6
is a monovalent hydrocarbon radical, preferably, having 1 to 18 carbon atoms per radical, which can be interrupted, if desired, by at least one oxygen atom,
d is 0, 1 or 2, and
e is 0, 1 or 2.
Surprisingly it has been found that the formation of a urethane from hydroxyl-containing iodonium salts makes it possible to reduce considerably the crystallization tendency, to improve substantially the compatibility with organopolysiloxanes containing epoxy groups, and to increase considerably the hydrolytic stability relative to iodonium salts containing Si—O—C bonds (see German Patent Application 19901531.7).
DESCRIPTION OF PREFERRED EMBODIMENTS
Preferred examples of aromatic hydrocarbon radicals Ar are the phenyl, naphthyl and anthryl radicals.
Preferred examples of aromatic hydrocarbon radicals Ar containing at least one oxygen and/or sulfur atom are the 2-furyl, 3-furyl, 2-thienyl and 3-thienyl radicals.
Preferred examples of the divalent hydrocarbon radical R
3
which can be interrupted by at least one oxygen atom and/or at least one sulfur atom and/or a carboxyl group are —CH
2
—, —CH
2
—CH
2
—, —CH
2
—CH
2
—O—CH
2
—CH
2
—, —CH
2
—CH(CH
3
)—, —CH
2
—CH(CH
2
CH
3
)—, —CH
2
—CH((CH
2
)
3
CH
3
)—, —CH
2
—CH((CH
2
)
11
CH
3
)—, —CH
2
—CH((CH
2
)
13
CH
3
)—, —CH
2
—CH
2
—S—CH
2
—CH
2
—, —CH
2
—O—C(O)—CH
2
—.
Preferred examples of R
4
, the monovalent linear, branched and/or cyclic alkyl, aryl, haloalkyl and/or haloaryl radical having 1 to 40 carbon atoms, which can be interrupted, if desired, by at least one oxygen atom and/or at least one sulfur atom and/or at least one urethane group and/or ester group, and which can, if desired, contain hydrophobicizing substituents and/or at least one isocyanate group, are alkyl radicals, such as the methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, and tert-pentyl radical; hexyl radicals, such as the n-hexyl radical, for example, the cyclohexyl radical; heptyl radicals, such as the n-heptyl radical; octyl radicals, such as the n-octyl radical and isooctyl radicals, such as the 2,2,4-trimethylpentyl radical; nonyl radicals, such as the n-nonyl radical; decyl radicals, such as the n-decyl radical; dodecyl radicals, such as the n-dodecyl radical, and octadecyl radicals, such as the n-octadecyl radical; aryl radicals, such as the phenyl, naphthyl and anthryl radical; haloalkyl radicals, such as the chloromethyl, trichloromethyl, trifluoromethyl, pentafluoroethyl and heptafluoropropyl radical; haloaryl radicals, such as the bromophenyl, chlorophenyl, fluorophenyl, difluorophenyl, fluoro(trifluoromethyl)phenyl, pentafluorophenyl, (trifluoromethyl)phenyl, (trifluoromethylthio)phenyl and trifluoromethoxyphenyl radical.
The abovementioned examples of the radical R
4
also apply in their entirety to the radicals R
5
and R
6
.
Examples of hydrocarbons R
4
, R
5
and R
6
interrupted by at least one oxygen atom and/or sulfur atom are —CH
2
—CH
2
—O—CH
3
, —CH
2
—CH
2
O—CH
2
CH
3
and —CH
2
—CH
2
—S—CH
2
CH
3
.
Examples of the radical R
4
inte

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