Photoinitiators for cationic curing

Details Photoinitiators for cationic curing Photoinitiators for cationic curing

2000-01-13

2002-04-02

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...

C522S025000, C522S170000, C522S181000, C522S185000, C522S099000, C522S148000, C528S012000, C528S013000, C528S019000, C528S023000, C528S033000, C528S040000, C528S032000, C556S400000, C556S402000, C556S463000, C556S482000, C556S486000, C556S009000

Reexamination Certificate

active

06365643

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to modified cationic photoinitiators possessing a reduced crystallization tendency, to a process for reducing the crystallization tendency of cationic photoinitiators, and to the use of the photoinitiators of the invention 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
+
—Ar MX
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-25 186 39, U.S. Pat. No. 4,279,717, EP-A-0 334 056, and EP-B-0 618 919) as well as their use as photoinitiators for polymerizing cationically polymerizable substances. The cationically polymerizable substances have, however, 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).
Diaryliodonium salts as described in U.S. Pat. No. 5,073,643 are likewise hydrophobically modified by alkyl chains. In addition, however, they carry a hydroxyl group. This results in deficient miscibility with organopolysiloxanes. After just a short time, turbidity and the precipitation of the photoinitiator are observed. Because of their inhomogeneity, such coatings do not cure very well under UV irradiation. It is also possible, however, for massive surface defects (craters, wrinkling, specks, etc.) to appear during the application of a thin layer on a substrate, as a result of the inhomogeneity.
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) results in a strong crystallization tendency in the compounds (A. Kunze, U. Müller, K. Tittes, J. P. Fonassier, 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 iodonium 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 under the trade name CD-1012 from Sartomer.
The high crystallization tendency has an adverse effect, however, when these 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.
OBJECT OF THE INVENTION
An object of the invention is 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 with organopolysiloxanes containing epoxy groups is established.
SUMMARY OF THE INVENTION
The above object is achieved in a first embodiment by means of cationic photoinitiators of the general formula IV
[R
1
—I—R
2
]
+
X
−
  (IV)
where I is the element iodine,
X
−
is the anion of a complex metal salt or of a strong acid,
R
1
is a radical
in which Ar is a monovalent aromatic hydrocarbon radical, preferably having 6 to 14 carbon atoms per radical, or is a monovalent 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 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 one sulfur atom and/or one carboxyl group,
R
a
, R
b
and R
c
each independently are selected from the group consisting of monovalent alkyl, aryl, haloalkyl and alkoxy radicals having 1 to 40 carbon atoms, preferably having 1 to 14 carbon atoms, and most preferably having 1 to 4 carbon atoms,
E is a radical
—O—R
d
,
F is a radical
—R
e
,
R
2
is a radical
 where
R
d
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
e
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,
f is 0, 1 or 2, and
g is 0, 1 or 2.
Surprisingly, it has been found that the modification of hydroxyl-containing cationic photoinitiators makes it possible to reduce considerably the crystallization tendency and to improve substantially the compatibility with organo-polysiloxanes containing epoxy groups.
DESCRIPTION OF THE 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 radicals R which can be interrupted by at least one oxygen atom and/or one sulfur atom and/or one carboxyl group are —CH
2
—, —CH
2
—CH
2
—, and —CH
2
—CH
2
—O—CH
2
—CH
2
—.
Preferred examples of hydrocarbon radicals R
a
, R
b
, R
c
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; 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; and aryl radicals such as the phenyl, naphthyl and anthryl radicals.
Preferably, all three radicals R
a
, R
b
, R
c
attached to the silicon atom together contain 3 to 25 carbon atoms.
The examples given above of the radicals R
a
, R
b
and R
c
also apply totally to the radicals R
d
and R
e
.
Preferred examples of hydrocarbon radicals R
d
and R
e
interrupted by at least one oxygen atom and/or one 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
3
.
Preferred examples of radicals D are
—O(CH
2
)
2
—O—Si(CH
3
)
3
—O(CH
2
)
2
—O—Si(CH
2
CH
3
)
3
—O(CH
2
)
2
—O—SiMe
2
Oct
—O—(CH
2
)
2
—O—SiMe
2
Ph
—O—(CH
2
)
2
—O—SiMePh
2
(in which Me is methyl radical, Et is ethyl radical, Ph is phenyl radical, and Oct is n-octyl radical).
Preferred examples of radicals E are the methoxy, ethoxy and n-butoxy radicals.
Preferred examples of radicals F are the methyl, ethyl, propyl, 2-methylpropyl and n-butyl radicals.
Preferred examples of radicals R
1
are
(in which Me, Et, Ph and Oct are each as defined above).
Preferred examples of radicals R
2
are the phenyl, 4-methylphenyl, 3-methoxyphenyl and 4-methoxyphenyl radical.
Preferred examples of anions X
−
of a complex metal salt or of a strong acid are tosylate, SbF
6
−
, PF
6
−
, BF
4
−
, F
3
CSO
3
−
, F
3
CCO
2
−
, AsF

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