Compounds of the formula I or I' ##STR1## in which R.sub.1 and R.sub.2 independently of one another, for example, are an aromatic hydrocarbon, with the proviso that the aromatic hydrocarbon radical is substituted in at least one o-position, or R.sub.1 and R.sub.2, for example, independently of one another are C.sub.1 -C.sub.20 alkyl, which is substituted by R.sub.9 R.sub.10 R.sub.11 Si; R.sub.2a is, for example, a divalent aromatic hydrocarbon radical; R.sub.3 is C.sub.1 -C.sub.20 alkyl which is substituted by R.sub.9 R.sub.10 R.sub.11 Si or is an aromatic hydrocarbon; R.sub.4 is, for example, C.sub.1 -C.sub.20 alkyl, C.sub.3 -C.sub.12 cycloalkyl or phenyl-C.sub.1 -C.sub.6 alkyl; E is R.sub.14 R.sub.15 R.sub.16 P or R.sub.8 R.sub.8a R.sub.7 N; R.sub.7, R.sub.8 and R.sub.8a and R.sub.9, R.sub.10 and R.sub.11 independently of one another are, for example, C.sub.1 -C.sub.12 alkyl; R.sub.14, R.sub.15 and R.sub.16 independently of one another are substituted phenyl and G is a radical which is able to form positive ions, with the proviso that, if R.sub.1, R.sub.2 and R.sub.3 are 2,4,6-trimethylphenyl, R.sub.4 is not C.sub.2 -C.sub.20 alkyl or C.sub.2 -C.sub.8 alkenyl, are suitable for use as particularly reactive photoinitiators.

The invention relates to highly reactive borate photoinitiator compounds, 
to compositions comprising these compounds, and to the use of the 
compounds. 
The use of borates as photoinitiators in combination with coinitiators is 
known in the prior art. For example, U.S. Pat. Nos. 4,772,530, 4,772,541 
and 5,151,520 disclose triaryl alkyl borate anions with cationic dyes, for 
example cyanines, rhodamines, etc., as counterions. These compounds are 
employed as photoinitiators. In U.S. Pat. No. 4,954,414, cationic 
transition metal complexes are used together with triaryl alkyl borate 
anions in photopolymerizable compositions. From U.S. Pat. No. 5,055,372 it 
is also known to use quaternary ammonium compounds, for example 
tetramethylammonium, pyridinium, cetylpyridinium, etc., as cationic 
counterions to the triaryl alkyl borate. 
In this publication, the borates are employed in association with aromatic 
ketone initiator compounds as coinitiators in photocurable materials. In 
EP-A-555 058 and JP-A Hei 5 255347, borates, including trimesityl butyl 
borate among others, are used as coinitiators for (oxo)sulfonium 
complexes. 
For the extensive range of applications of photoinitiators, there is a 
requirement in the industry for stable reactive compounds. 
It has surprisingly now been found that monoborate compounds which are 
ortho-substituted on at least two aryl radicals possess these properties 
to a high degree. The invention therefore provides compounds of the 
formulae I and I' 
##STR2## 
in which 
R.sub.1 and R.sub.2 independently of one another are phenyl or another 
aromatic hydrocarbon, with or without any heteroatom, which radicals are 
unsubstituted or are substituted 1-5 times by C.sub.1 -C.sub.20 alkyl, 
C.sub.2 -C.sub.20 alkyl which is interrupted by one or more radicals O, 
S(O).sub.p or NR.sub.5, or are substituted by OR.sub.6, R.sub.6 
S(O).sub.p, R.sub.6 S(O).sub.2 O, R.sub.7 R.sub.8 N, R.sub.6 OC(O), 
R.sub.7 R.sub.8 NC(O), R.sub.9 C(O), R.sub.9 R.sub.10 R.sub.11 Si, R.sub.9 
R.sub.10 R.sub.11 Sn, R.sub.12 R.sub.13 B, halogen, R.sub.9 R.sub.10 
P(O).sub.q, and/or CN, 
with the proviso that the phenyl radical or the other aromatic hydrocarbon 
radicals are substituted in at least one o-position, or R.sub.1 and 
R.sub.2 independently of one another are C.sub.1 -C.sub.20 alkyl which is 
substituted by R.sub.9 R.sub.10 R.sub.11 Si, or the radicals R.sub.1 and 
R.sub.2 form bridges to produce structures of the formula II, IIa or IIb 
##STR3## 
where the aromatic rings in the formulae II, IIa or IIb are unsubstituted 
or are substituted by C.sub.1 -C.sub.20 alkyl, C.sub.2 -C.sub.20 alkyl 
which is interrupted by one or more radicals O, S(O).sub.p or NR.sub.5 or 
are substituted by OR.sub.6, R.sub.6 S(O).sub.p, R.sub.6 S(O).sub.2 O, 
R.sub.7 R.sub.8 N, R.sub.6 OC(O), R.sub.7 R.sub.8 NC(O), R.sub.9 C(O), 
R.sub.9 R.sub.10 R.sub.11 Si, R.sub.9 R.sub.10 R.sub.11 Sn, halogen, 
R.sub.9 R.sub.10 P(O).sub.q and/or R.sub.12 R.sub.13 B; 
R.sub.2a is phenylene or another divalent aromatic hydrocarbon, with or 
without any heteroatom, which radicals are unsubstituted or are 
substituted 1-5 times by C.sub.1 -C.sub.20 alkyl, C.sub.2 -C.sub.20 alkyl 
which is interrupted by one or more radicals O, S(O).sub.p or NR.sub.5, or 
are substituted by OR.sub.6, R.sub.6 S(O)p, R.sub.6 S(O).sub.2 O, R.sub.7 
R.sub.8 N, R.sub.6 OC(O), R.sub.7 R.sub.8 NC(O), R.sub.9 C(O), R.sub.9 
R.sub.10 R.sub.11 Si, R.sub.9 R.sub.10 R.sub.11 Sn, R.sub.12 R.sub.13 B, 
halogen, R.sub.9 R.sub.10 P(O).sub.q, and/or CN, or R.sub.2a is 
phenyl-C.sub.1 -C.sub.6 alkylene; 
R.sub.3 is C.sub.1 -C.sub.20 alkyl which is substituted by R.sub.9 R.sub.10 
R.sub.11 Si, or is phenyl or another aromatic hydrocarbon, with or without 
any heteroatom, where the phenyl radical or the other aromatic hydrocarbon 
radicals are unsubstituted or are substituted 1-5 times by C.sub.1 
-C.sub.20 alkyl, C.sub.2 -C.sub.20 alkyl which is interrupted by one or 
more radicals O, S(O).sub.p or NR.sub.5, or are substituted by OR.sub.6, 
R.sub.6 S(O).sub.p, R.sub.6 S(O).sub.2 O, R.sub.7 R.sub.8 N, R.sub.6 
OC(O), R.sub.7 R.sub.8 NC(O), R.sub.9 C(O), R.sub.9 R.sub.10 R.sub.11 Si, 
R.sub.9 R.sub.10 R.sub.11 Sn, R.sub.12 R.sub.13 B, halogen, R.sub.9 
R.sub.10 P(O).sub.q, and/or CN; 
R.sub.4 is phenyl, another aromatic hydrocarbon, C.sub.1 -C.sub.20 alkyl, 
C2-C.sub.20 alkyl which is interrupted by one or more radicals O, 
S(O).sub.p or NR.sub.5, or is C.sub.3 -C.sub.12 cycloalkyl, C.sub.2 
-C.sub.8 alkenyl, phenyl-C.sub.1 -C.sub.6 alkyl or naphthyl-C.sub.1 
-C.sub.3 alkyl, where the radicals phenyl, another aromatic hydrocarbon, 
C.sub.1 -C.sub.20 alkyl, C.sub.3 -C.sub.12 cycloalkyl, C.sub.2 -C.sub.8 
alkenyl, phenyl-C.sub.1 -C.sub.6 alkyl or naphthyl-C.sub.1 -C.sub.3 alkyl 
are unsubstituted or are substituted by OR.sub.6, R.sub.6 S(O).sub.p, 
R.sub.6 S(O).sub.2 O, R.sub.7 R.sub.8 N, R.sub.6 OC(O), R.sub.7 R.sub.8 
NC(O), R.sub.9 C(O), R.sub.9 R.sub.10 R.sub.11 Si, R.sub.9 R.sub.10 
R.sub.11 Sn, R.sub.12 R.sub.13 B, halogen, R.sub.9 R.sub.10 P(O).sub.q, 
and/or CN; 
E is R.sub.14 R.sub.15 R.sub.16 P, R.sub.6 R.sub.6a S or R.sub.8 R.sub.8a 
R.sub.7 N; 
Y is (CH.sub.2).sub.n, CH.dbd.CH, C(O), NR.sub.5, O, S(O).sub.p or 
##STR4## 
n is 0, 1 or 2; 
m is 2 or 3; 
p is 0, 1 or 2; 
q is 0 or 1; 
R.sub.5 is hydrogen, C.sub.1 -C.sub.12 alkyl, phenyl-C.sub.1 -C.sub.6 alkyl 
or phenyl, where the radicals phenyl-C.sub.1 -C.sub.6 alkyl or phenyl are 
unsubstitued or are substituted 1-5 times by C.sub.1 -C.sub.6 alkyl, 
C.sub.1 -C.sub.12 alkoxy and/or halogen; 
R.sub.6 and R.sub.6a independently of one another are C.sub.1 -C.sub.12 
alkyl, phenyl-C.sub.1 -C.sub.6 alkyl or phenyl, where the radicals 
phenyl-C.sub.1 -C.sub.6 alkyl or phenyl are unsubstituted or are 
substituted 1-5 times by C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.12 alkoxy 
and/or halogen; 
R.sub.7, R.sub.8 and R.sub.8a independently of one another are C.sub.1 
-C.sub.12 alkyl, C.sub.3 -C.sub.12 cycloalkyl, phenyl-C.sub.1 -C.sub.6 
alkyl or phenyl where the radicals phenyl-C.sub.1 -C.sub.6 alkyl or phenyl 
are unsubstituted or are substituted 1-5 times by C.sub.1 -C.sub.6 alkyl, 
C.sub.1 -C.sub.12 alkoxy, R.sub.6 OC(O), CN and/or halogen or R.sub.7 and 
R.sub.8 together with the N atom to which they are attached, form a 5- or 
6-membered ring which may additionally contain O or S atoms; 
R.sub.9, R.sub.10 and R.sub.11 independently of one another are C.sub.1 
-C.sub.12 alkyl, C.sub.3 -C.sub.12 cycloalkyl, phenyl-C.sub.1 -C.sub.6 
alkyl or phenyl, where the radicals phenyl-C.sub.1 -C.sub.6 alkyl or 
phenyl are unsubstituted or are substituted 1-5 times by C.sub.1 -C.sub.6 
alkyl, C.sub.1 -C.sub.12 alkoxy and/or halogen; 
R.sub.12 and R.sub.13 independently of one another are C.sub.1 -C.sub.12 
alkyl, C.sub.3 -C.sub.12 cycloalkyl, phenyl-C.sub.3 -C.sub.6 alkyl or 
phenyl where the radicals phenyl C.sub.1 -C.sub.6 alkyl or phenyl are 
unsubstituted or are substituted 1-5 times by C.sub.1 -C.sub.6 alkyl, 
C.sub.1 -C.sub.12 alkoxy and/or halogen, or R.sub.12 and R.sub.13, 
together with the B atom to which they are attached, form a 5- or 
6-membered ring; 
R.sub.14, R.sub.15 and R.sub.16 independently of one another are C.sub.1 
-C.sub.12 alkyl, C.sub.2 -C.sub.12 alkenyl, C.sub.3 -C.sub.12 cycloalkyl, 
where the radicals C.sub.1 -C.sub.12 alkyl, C.sub.2 -C.sub.12 alkenyl, 
C.sub.3 -C.sub.12 cycloalkyl are unsubstituted or are substituted by 
R.sub.6 OCO or CN, or R.sub.14, R.sub.15 and R.sub.16 are phenyl-C.sub.1 
-C.sub.6 alkyl, which is unsubstituted or is substituted one to five times 
by C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.12 alkoxy or halogen, or are 
phenyl which is unsubstituted or is substituted one to five times by 
C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.12 -alkoxy or halogen; and 
G is a radical which is able to form positive ions, 
with the proviso that, if R.sub.1, R.sub.2 and R.sub.3 are 
2,4,6-trimethylphenyl, R.sub.4 is not C.sub.2 -C.sub.20 alkyl or C.sub.2 
-C.sub.8 alkenyl. 
In combination with coinitiators these compounds are highly reactive 
initiators for the photopolymerization of ethylenically unsaturated 
compounds. 
In the compounds of the formula I, at least one of the radicals R.sub.1 and 
R.sub.2, provided that they are not R.sub.9,R.sub.10 R.sub.11 Si 
substituted C.sub.1 -C.sub.20 alkyl, are each a phenyl ring which is 
substituted ortho to the bond to the boron atom or is another aromatic 
hydrocarbon radical which is sterically hindered ortho to the boron atom. 
Ortho-substitution here is generally understood to mean a bond in the o 
position of the aryl ring with respect to the boron central atom, thus 
including, for example, a fused-on ring. In accordance with this 
definition, therefore, some polycyclic aromatic hydrocarbons, for example 
naphthyl, are also rings (ring systems) which are substituted ortho to the 
bond to the boron central atom. 
Aromatic hydrocarbons as may be present in the novel compounds may, for 
example, contain one or more, especially 1 or 2, heteroatoms. Examples of 
suitable heteroatoms are N, O, P or S, preferably N or O. Examples of 
aromatic hydrocarbon radicals are phenyl, .alpha.- and .beta.-naphthyl, 
stilbenyl, biphenyl, o-, m-, p-terphenyl, triphenylphenyl, binaphthyl, 
anthracyl, phenanthryl, pyrenyl, furan-2-yl or furan-3-yl, thiophen-2-yl 
or thiophen-3-yl, pyridin-2-yl, pyridin-3-yl or pyridin-4-yl quinolyl or 
isoquinolyl. 
##STR5## 
If the radicals phenyl, stilbenyl, biphenyl, o-, m- or p-terphenyl, 
triphenylphenyl, naphthyl, binaphthyl, anthracyl, phenanthryl, pyrenyl, 
ferrocenyl, furanyl, thiophenyl, pyridinyl, quinolinyl or isoquinolinyl 
are substituted, they are so one to four times, for example one, two or 
three times, especially one or two times. Substituents on the phenyl ring 
are preferably in positions 2, or in 2,6 or 2,4,6 on the phenyl ring. 
C.sub.1 -C.sub.20 alkyl is linear or branched and is, for example, C.sub.1 
-C.sub.12, C.sub.1 -C.sub.8, C.sub.1 -C.sub.6 or C.sub.1 -C.sub.4 alkyl. 
Examples are methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, 
isobutyl, tert-butyl, pentyl, hexyl, heptyl, 2,4,4-trimethylpentyl, 
2-ethylhexyl, octyl, nonyl, decyl, undecyl, dodecyl, tetradecyl, 
pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl or eicosyl. For 
example, R.sub.4 is C.sub.1 -C.sub.8 alkyl, in particular C.sub.1 -C.sub.6 
alkyl, preferably C.sub.1 -C.sub.4 alkyl, for example methyl or butyl. 
Where R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are R.sub.9 R.sub.10 R.sub.11 
Si substituted C.sub.1 -C.sub.20 alkyl, then the alkyl radical is, for 
example, C.sub.1 -C.sub.12 alkyl, especially C.sub.1 -C.sub.8 alkyl, 
preferably C.sub.1 -C.sub.4 alkyl. Methyl is particularly preferred. 
C.sub.1 -C.sub.12 alkyl and C.sub.1 -C.sub.6 alkyl are likewise linear or 
branched and have, for example, the definitions indicated above up to the 
corresponding number of C atoms. R.sub.5, R.sub.6, R.sub.7, R.sub.8, 
R.sub.9, R.sub.10, R.sub.11, R.sub.12 and R.sub.13 are, for example, 
C.sub.1 -C.sub.8 alkyl, especially C.sub.1 -C.sub.6 alkyl, preferably 
C.sub.1 -C.sub.4 alkyl, for example methyl or butyl. C.sub.1 -C.sub.6 
alkyl substituents for phenyl-C.sub.1 -C.sub.6 alkyl or phenyl are, in 
particular, C.sub.1 -C.sub.4 alkyl, for example methyl or butyl. 
C.sub.2 -C.sub.20 alkyl which is interrupted one or more times by --O--, 
--S(O).sub.p -- or --NR.sub.5 -- is, for example, interrupted 1-9 times, 
for example 1-7 times or 1 or 2 times, by --O--, --S(O).sub.p -- or 
--NR.sub.5. This produces structural units such as, for example, 
--CH.sub.2 --O--CH.sub.3, --CH.sub.2 CH.sub.2 --O--CH.sub.2 CH.sub.3, 
--CH.sub.2 CH.sub.2 O!.sub.y --CH.sub.3, where y=1-9, --(CH.sub.2 
CH.sub.2 O).sub.7 CH.sub.2 CH.sub.3, --CH.sub.2 
--CH(CH.sub.3)--O--CH.sub.2 --CH.sub.2 --CH.sub.3, --CH.sub.2 
--CH(CH.sub.3)--O--CH.sub.2 --CH.sub.3, --CH.sub.2 SCH.sub.3 or --CH.sub.2 
--N(CH.sub.3).sub.2. 
C.sub.3 -C.sub.12 Cycloalkyl is, for example, cyclopropyl, cyclopentyl, 
cyclohexyl, cyclooctyl, cyclododecyl, especially cyclopentyl and 
cyclohexyl, preferably cyclohexyl. 
C.sub.2 -C.sub.8 alkenyl radicals can be mono- or polyunsaturated and are, 
for example, allyl, methallyl, 1,1-dimethylallyl, 1-butenyl, 3-butenyl, 
2-butenyl, 1,3-pentadienyl, 5-hexenyl or 7-octenyl, especially allyl. 
R.sub.4 as C.sub.2 -C.sub.8 alkenyl is for example C.sub.2 -C.sub.6 
alkenyl, especially C.sub.2 -C.sub.4 alkenyl. 
Phenyl-C.sub.1 -C.sub.6 alkyl is, for example, benzyl, phenylethyl, 
.alpha.-methylbenzyl, phenylpentyl, phenylhexyl or 
.alpha.,.alpha.-dimethylbenzyl, especially benzyl. Preference is given to 
phenyl-C.sub.1 -C.sub.4 alkyl, especially phenyl-C.sub.1 -C.sub.2 alkyl. 
Substituted phenyl-C.sub.1 -C.sub.6 alkyl is substituted one to four 
times, for example once, twice or three times, especially once or twice, 
on the phenyl ring. 
Phenyl-C.sub.1 -C.sub.6 alkylene has two free bonds of which one is on the 
phenylene ring and the other in the alkylene radical: 
##STR6## 
where x=1 to 6. 
Substitututed phenyl is substituted one to five times, for example once, 
twice or three times, especially once or twice, on the phenyl ring. 
Naphthyl-C.sub.1 -C.sub.3 alkyl is for example, naphthylmethyl, 
naphthylethyl, naphthylpropyl or naphthyl-1-methylethyl, especially 
naphthylmethyl. The alkyl unit can be in either position 1 or position 2 
of the naphthyl ring system. Substituted naphthyl-C.sub.1 -C.sub.3 alkyl 
is substituted one to four times, for example once, twice or three times, 
especially once or twice, on the aromatic rings. 
C.sub.1 -C.sub.12 alkoxy denotes linear or branched radicals and is, for 
example, methoxy, ethoxy, propoxy, isopropoxy, n-butyloxy, sec-butyloxy, 
iso-butyloxy, tert-butyloxy, pentyloxy, hexyloxy, heptyloxy, 
2,4,4-trimethylpentyloxy, 2-ethylhexyloxy, octyloxy, nonyloxy, decyl-oxy 
or dodecyloxy, especially methoxy, ethoxy, propoxy, isopropoxy, 
n-butyloxy, sec-butyloxy, iso-butyloxy, tert-butyloxy, preferably methoxy. 
Halogen is fluorine, chlorine, bromine and iodine, especially fluorine, 
chlorine and bromine, preferably fluorine and chlorine. 
Where C.sub.1 -C.sub.20 alkyl is substituted one or more times by halogen, 
there are, for example, 1 to 3 or 1 or 2 halogen substituents on the alkyl 
radical. 
Where R.sub.7 and R.sub.8, together with the N atom to which they are 
attached, form a 5- or 6-membered ring which may additionally contain O or 
S atoms, then the rings involved are, for example, saturated or 
unsaturated rings, for example aziridine, pyrrol, pyrrolidine, oxazole, 
thiazole, pyridine, 1,3-diazine, 1,2-diazine, piperidine or morpholine. 
Radicals generally suitable as a counterion G.sup.+ to the negative borate 
in the formula I are those which are able to form positive ions. 
Examples of these are alkali metals, especially lithium or sodium, 
quaternary ammonium compounds, dye cations or cationic transition metal 
coordination complex compounds. Especially preferred are ammonium, 
tetraalkylammonium or dye cations. Examples of tetraalkylammonium are, in 
particular, tetramethylammonium or tetrabutylammonium, although 
trisalkylammonium ions, for example trimethylammonium, are also suitable. 
Suitable phosphonium and ammonium counterions are those of the formulae 
.sup.+ PR.sub.w R.sub.x R.sub.y R.sub.z and .sup.+ NR.sub.w R.sub.x 
R.sub.y R.sub.z, where R.sub.w, R.sub.x, R.sub.y, R.sub.z, independently 
of one another are hydrogen, unsubstituted or substituted alkyl, 
cycloalkyl, alkenyl, phenyl or arylalkyl. Substituents for these alkyl, 
cycloalkyl, alkenyl, phenyl or arylalkyl radicals are, for example, 
halide, hydroxyl, heterocycloalkyl (e.g. epoxy, aziridyl, oxetanyl, 
furanyl, pyrrolidinyl, pyrrolyl, thiophenyl, tetrahydrofuranyl, etc.), 
dialkylamino, amino, carboxyl, alkyl- and arylcarbonyl and aryloxy- and 
alkoxycarbonyl. 
The tetravalent nitrogen may also be part of a 5- or 6-membered ring, in 
which case this ring may in turn be fused to other ring systems. These 
systems may also contain additional heteroatoms, for example S, N, O. 
The tetravalent nitrogen may also be part of a polycyclic ring system, for 
example azoniapropellane. These systems may also contain further 
heteroatoms, for example S, N, O. 
Also suitable are polyammonium salts and polyphosphonium salts, especially 
the bis salts, in which it is possible for the same substituents to be 
present as described above for the "mono" compounds 
The ammonium salts and phosphonium salts may also be substituted by neutral 
dyes (e.g. thioxanthenenes, thioxanthones, coumarins, ketocoumarins, 
etc.). Such salts are obtained by the reaction of the ammonium salts and 
phosphonium salts, substituted by reactive groups (e.g. epoxy, amino, 
hydroxyl, etc.), with appropriate derivatives of neutral dyes. 
Corresponding examples are described in EP-A 224 967 (Quantacure QTX). 
Similarly, ammonium salts and phosphonium salts can also be substituted by 
colourless electron acceptors (e.g. benzophenones); examples of these are 
Quantacure ABQ 
##STR7## 
Other quaternary ammonium compounds which are of interest are, for example, 
trimethylcetylammonium or cetylpyridinium compounds. 
Other examples to be used as positive counterions G.sup.+ in the compound 
of the formual I include the following: 
##STR8## 
in which Z is P, N or S and R is an alkyl or aryl radical. Also suitable 
are compounds such as 
##STR9## 
(described by Yagci et al. in J. Polym. Sci. Part A: Polymer Chem. 1992, 
30, 1987 and Polymer 1993, 34(6), 1130) or compounds such as 
##STR10## 
where R'=unsubstituted or substituted benzyl or phenacyl (described in 
JP-A Hei 7 70221). In these compounds, the aromatic rings in the 
pyridinium may also be substituted. 
The term tetra (C.sub.1 -C.sub.4 alkyl)ammonium refers to compounds of the 
following formula: N(C.sub.1 -C.sub.4 alkyl).sup.+.sub.4, where C.sub.1 
-C.sub.4 alkyl can have the definitions given above up to the 
corresponding number of C atoms. Examples of appropriate ammonium 
compounds are tetramethylammonium, tetraethylammonium, tetrapropylammonium 
or tetrabutylammonium, especially tetramethylammonium and 
tetrabutylammonium. Benzyltri(C.sub.1 -C.sub.4 alkyl)ammonium is C.sub.6 
H.sub.5 --CH.sub.2 --N(C.sub.1 -C.sub.4 alkyl).sub.3.sup.+, where C.sub.1 
-C.sub.4 alkyl can have the definitions given above up to the 
corresponding number of C atoms. Examples of such radicals are 
benzyltrimethylammonium, benzyltriethylammonium, benzyltripropylammonium 
and benzylbutylammonium, especially benzyltrimethylammonium and 
benzyltributylammonium. 
Other positive counterions G.sup.+ to the borate which can be employed are 
other onium ions, for example iodonium or sulfonium ions. 
Examples of such counterions to the borate are radicals of the formula 
##STR11## 
as described, for example, in EP-A 555 058 and EP-A 690 074. Also of 
interest as counterions are 
##STR12## 
Further suitable counterions for the novel borates are cations of the 
formula 
##STR13## 
in which R.sub.9 is an alkyl radical, especially ethyl, or benzyl, and 
where the aromatic ring can carry further substituents. 
Other suitable counterions are halonium ions, especially diaryliodonium 
ions, as described for example in EP-A 334 056 and EP-A 562 897. 
However, cations of ferrocenium salts are also suitable, as described, for 
example, in EP-A 94915 and EP-A 109 851, for example 
##STR14## 
Other suitable "onium" cations, such as ammonium, phosphonium, sulfonium, 
iodonium, selonium, arsonium, tellonium and bismuthonium, are described, 
for example, in Japanese Patent Application Hei 6 266102. 
Examples of cationic transition metal complex compounds which are suitable 
as counterions are described in U.S. Pat. No. 4,954,414. Of particular 
interest are bis(2,2'-bipyridine)(4,4'-dimethyl-2,2'-bipyridine)ruthenium, 
tris(4,4'-dimethyl-2,2'-bipyridine)ruthenium, 
tris(4,4'-dimethyl-2,2'-bipyridine)iron, 
tris(2,2',2"-terpyridine)ruthenium, tris(2,2'-bipyridine)ruthenium and 
bis(2,2'-bipyridine)(5-chloro-1,10-phenanthroline)ruthenium. 
Dyes suitable as a counterion are those without acid groups, for example 
cations of triarylmethanes, for example malachite green, indolines, 
thiazines, for example methylene blue, xanthones, thioxanthones, oxazines, 
acridines, cyanines, rhodamines, phenazines, for example safranine, 
preferably cyanines, thioxanthones and safranine. 
If the compounds of the formula I do not contain a dye as counterion and at 
the same time the corresponding borate is not sufficiently absorptive, 
then for the photopolymerization process it is expedient to add at least 
one coinitiator or electron aceptor compound, respectively. In this 
application the term coinitiator includes sensitizers and electron aceptor 
compounds, for example thioxanthones, reaction accelerators, for example 
amines, thiols, etc. Preferred are dyes. Examples of suitable dyes which 
can be added as coinitiators are described in U.S. Pat. No. 5,151,520. 
They are, for example, triarylmethanes, for example malachite green, 
indolines, thiazines, for example methylene blue, xanthones, 
thioxanthones, oxazine, acridine or phenazines, for example safranin. The 
above-described transition metal complex compounds or onion ion compounds 
can also be used as coinitiator. 
Cationic, neutral or anionic dyes can be employed as coinitiators for the 
novel compounds. Particularly suitable cationic dyes are malachite green, 
methylene blue, safranin O, rhodamines of the formula III 
##STR15## 
in which R and R' are alkyl radicals or aryl radicals, for example 
rhodamine B, rhodamine 6G or violamine R, and also sulforhodamine B or 
sulforhodamine G. 
Other suitable dyes are fluorones, as described for example by Neckers et 
al. in J. Polym. Sci., Part A, Poly. Chem, 1995, 33, 1691-1703. 
##STR16## 
is particularly advantageous. 
Examples of further suitable dyes are cyanines of the formula IV 
##STR17## 
in which R=alkyl; n=0,1,2,3 or 4 and Y.sub.1 =CH.dbd.CH, N--CH.sub.3, 
C(CH.sub.3).sub.2, O, S or Se. Preferred cyanines are those in which 
Y.sub.1 in formula IV is C(CH.sub.3).sub.2 or S. 
The following dye compounds are also suitable as coinitiators: 
##STR18## 
in which Z is P, N or S and R is an alkyl or aryl radical. Preferred 
compounds of the above formulae are those in which ZR.sub.3 is 
N(CH.sub.3).sub.3, N(C.sub.2 H.sub.5).sub.3 or P(C.sub.6 H.sub.5).sub.3. 
Also suitable are compounds such as, for example, 
##STR19## 
as described for example by Yagci et al. in J. Polym. Sci. Part A: Polymer 
Chem. 1992, 30, 1987 and Polymer 1993, 34(6),1130, or, for example, 
##STR20## 
where R'=unsubstituted or substituted benzyl or phenacyl (described in 
JP-A Hei 7 70221). In these compounds, the aromatic pyridinium rings may 
also be substituted. 
Other suitable dyes can be found, for example, in U.S. Pat. No. 4,902,604. 
These are azulene dyes. Of particular advantage as coinitiators for the 
novel compounds are the compounds 1-18 listed in columns 10 and 11 of this 
patent, in the Table. Examples of further suitable dyes are merocyanine 
dyes, as described in U.S. Pat. No. 4,950,581 from column 6, line 20 to 
column 9, line 57. 
As coinitiators for the novel compounds and photoinitiators it is also 
possible to use coumarin compounds. Examples of these are given in U.S. 
Pat. No. 4,950,581 in column 11, line 20 to column 12, line 42. 
Other suitable coinitiators are xanthones or thioxanthones as described, 
for example, in U.S. Pat. No. 4,950,581, column 12, line 44 to column 13, 
line 15. 
Anionic dye compounds can also be employed as coinitiators. For instance, 
Rose Bengal, eosine or fluorescein are also suitable as coinitiators. 
Other suitable dyes, for example from the triarylmethane class or azo 
class, are described in U.S. Pat. No. 5,143,818. 
Other suitable electron acceptor compounds are indicated later on below. 
Preference is given to compounds of the formula I in which R.sub.1 and 
R.sub.2 independently of one another are phenyl which is substituted in at 
least one o-position by C.sub.1 -C.sub.6 alkyl, ORO.sub.6, R.sub.7 R.sub.8 
N, R.sub.9 R.sub.10 R.sub.11 Si and/or halogen, or R.sub.1 and R.sub.2 are 
o-terphenyl, naphthyl, binaphthyl, anthracyl, phenanthryl, pyrenyl, 
quinolinyl or isoquinolyl which radicals are unsubstituted or are 
substituted by C.sub.1 -C.sub.6 alkyl, OR.sub.6, R.sub.7 R.sub.8 N, 
R.sub.9 R.sub.10 R.sub.11 Si and/or halogen. 
Further advantageous compounds of the formula I are those in which R.sub.3 
is phenyl, o-, m- or p-terphenyl, naphthyl, binaphthyl, anthracyl, 
phenanthryl, pyrenyl, quinolyl or isoquinolyl, which radicals are 
unsubstituted or substituted by C.sub.1 -C.sub.6 alkyl, OR.sub.6, R.sub.7 
R.sub.8 N, R.sub.9 R.sub.10 R.sub.11 Si and/or halogen. 
Compounds of the formula I deserving particular mention are those in which 
R.sub.4 is phenyl, another aromatic hydrocarbon, C.sub.1 -C.sub.12 alkyl, 
C.sub.2 -C.sub.12 alkyl, which is interrupted by one or more O or NR.sub.5 
radicals, or is cyclopentyl, cyclohexyl, C.sub.2 -C.sub.12 alkenyl, benzyl 
or phenylethyl, which radicals are unsubstituted or are substituted by 
OR.sub.6, R.sub.7 R.sub.8 N, R.sub.9 R.sub.10 R.sub.11 Si and/or halogen. 
Particular preference is given to those compounds of the formula I in which 
R.sub.1, R.sub.2 and R.sub.3 independently of one another are C.sub.1 
-C.sub.20 alkyl which is substituted by R.sub.9 R.sub.10 R.sub.11 Si. 
Advantageous compounds of the formula I are those in which R.sub.4 is 
C.sub.1 -C.sub.20 alkyl, substituted by R.sub.9 R.sub.10 R.sub.11 Si. 
Preference is also given to the compounds of the formel I in which R.sub.1 
and R.sub.2 are identical. 
Preference is likewise given to compounds of the formula I in which 
R.sub.1, R.sub.2 and R.sub.3 are identical. 
Further preferred compounds of the formula I are those in which G is an 
alkali metal, a quaternary ammonium radical, a dye cation, a transition 
metal complex cation, a sulfonium, sulfoxonium, phosphonium or iodonium 
salt or a UV absorber containing a cationic group, or are a radical MgX or 
CaX, in which X is C.sub.1 -C.sub.8 alkoxy or halogen. 
Other compounds of the formula I or I' which are of interest are those in 
which R.sub.1 and R.sub.2 are C.sub.1 -C.sub.4 alkyl which are substituted 
by R.sub.9 R.sub.10 R.sub.11 Si or are phenyl which is substituted 1-5 
times by C.sub.1 -C.sub.4 alkyl, OR.sub.6 and/or halogen; R.sub.2a is 
phenylene; R.sub.3 is C.sub.1 -C.sub.4 alkyl which is substituted by 
R.sub.9 R.sub.10 R.sub.11 Si, or is phenyl which is unsubstituted or is 
substituted 1-5 times by C.sub.1 -C.sub.4 alkyl, OR.sub.6, R.sub.7 R.sub.8 
N and/or halogen; 
R.sub.4 is unsubstituted or R.sub.9 R.sub.10 R.sub.11 Si substituted 
C.sub.1 -C.sub.4 alkyl or unsubstituted or halogen-substituted phenyl; 
m is 2 or 3; E is R.sub.8 R.sub.8a R.sub.7 N; R.sub.6 is C.sub.1 -C.sub.4 
alkyl; R.sub.7, R.sub.8 and R.sub.8a, independently of one another are 
C.sub.1 -C.sub.4 alkyl or benzyl; R.sub.9, R.sub.10 and R.sub.11 are 
C.sub.1 -C.sub.4 alkyl and G is tetra(C.sub.1 -C.sub.4 alkyl)ammonium or 
benzyl-tri(C.sub.1 -C.sub.4 alkyl)ammonium. 
The compounds of the formula I can be obtained, for example, by reacting 
triorganylboranes (A) with organometallic reagents, for example 
alkyllithium compounds or Grignard reagents: 
##STR21## 
M is, for example, an alkali metal, such as Li or Na, or is MgX in which X 
is a halogen atom, especially Br. 
Another possibility for preparing compounds of the formula I is, for 
example, the reaction of alkyldihaloboranes and alkyloxy- or 
aryloxydihaloboranes (B) with organometallic compounds, for example, 
Grignard reagents or lithium organyl compounds: 
##STR22## 
X is halogen, especially Br, and X' is halogen, alkoxy or aryloxy. The 
definitions of the other radicals are as indicated above. 
Where G in the above formula I is a positive radical other than lithium or 
magnesium, these compounds can be obtained, for example, by means of 
cation exchange reactions. 
The compounds of the formula I' are obtained, for example, by reacting 
triorganylboranes which are substituted by the group E as defined above to 
the borate in accordance with one of the methods set out above. 
When working with organometallic reactions, the reaction conditions are 
generally familiar to the skilled worker. Thus the reaction is expediently 
carried out in an inert organic solvent, for example an ether or aliphatic 
hydrocarbon, for example diethyl ether, tetrahydrofuran or hexane. 
Suitable organometallic reagents for preparing the novel polyborates are, 
for example, the lithium compounds of the corresponding aliphatic and 
aromatic hydrocarbons. The preparation of Grignard reagents is familiar to 
the skilled worker and is described in various textbooks and other 
publications. 
The reaction with the organometallic reagent is expediently carried out 
with the exclusion of air in an inert gas atmosphere, for example under 
nitrogen. The reaction is generally performed with cooling to 0.degree. C. 
or below followed by heating to room temperature. 
It is expedient to stir the reaction mixture. The products are isolated and 
purified by methods likewise generally known to the skilled worker, for 
example chromatography, recrystallization, etc. 
Where the novel compounds of the formula I contain a dye radical as cation, 
they are prepared by the cation exchange reaction of an appropriate borate 
salt with a dye. Examples of the borate salts suitable for the exchange 
are the lithium, magnesium, sodium, ammonium or tetraalkylammonium salts. 
Where the novel compounds of the formula I contain a transition metal 
complex as cation, these compounds are prepared in analogy to the method 
described in U.S. Pat. No. 4,954,414, column 7, section 2. 
Preparation of triorganylboranes (A): The preparation of some 
alkyldiarylboranes is described, for example, by A. Pelter et al. in 
Tetrahedron 1993, 49, 2965. The synthesis of some triarylboranes has been 
disclosed by Doty et al. in J. Organomet. Chem. 1972, 38, 229, by Brown et 
al. in J. Organomet. Chem. 1981, 209, 1, Brown et al. in J. Amer. Chem. 
Soc. 1957, 79, 2302, and by Wittig et al. in Chem. Ber. 1955, 88, 962. 
Preparation of aryldihaloboranes (B): The route to some alkyldihaloboranes 
(B) has been depicted by Brown et al. in JACS 1977, 99, 7097. Mikailov et 
al. in Zh. Obshch. Khim. 1959, 29, 3405 and Tuchagues et al. in Bull. 
Chim. Soc. France, 1967, 11, 4160 also describe the preparation of such 
compounds. The preparation of phenyldifluoroborane has been set out by 
Nahm et al. in J. Organomet. Chem. 1972, 35, 9. 
Tris(trimethylsilylmethyl)boranes can be prepared, for example, by the 
method described by Seyferth et al. in J. Amer. Chem. Soc. 1959, 81, 1844. 
The boranes required as starting materials for the novel compounds can be 
obtained, for example, in accordance with one of the published methods 
cited above. 
In accordance with the invention the compounds of the formula I can be used 
as photoinitiators for the photopolymerization of ethylenically 
unsaturated compounds and mixtures comprising such compounds. 
This can be carried out in combination with at least one coinitiator or 
electron acceptor respectively. 
This use can also be implemented in combination with another photoinitiator 
and/or other additives. 
The invention therefore also relates to photopolymerizable compositions 
comprising 
(a) at least one ethylenically unsaturated photopolymerizable compound and 
(b) at least one compound of the formula Ia or Ia' 
##STR23## 
in which 
R.sub.1, R.sub.2, R.sub.2a, R.sub.4, E and G are as defined above and 
R.sub.3 ' is R.sub.9 R.sub.10 R.sub.11 Si substituted C.sub.1 -C.sub.20 
alkyl, C.sub.1 -C.sub.4 alkyl, phenyl or another aromatic hydrocarbon, 
with or without any heteroatom, where the phenyl radical or the other 
aromatic hydrocarbon radicals are unsubstituted or are substituted 1-5 
times by C.sub.1 -C.sub.20 alkyl, C.sub.2 -C.sub.20 alkyl which is 
interrupted by one or more radicals O, S(O)p or NR.sub.5, or are 
substituted by OR.sub.6, R.sub.6 S(O).sub.p, R.sub.6 S(O).sub.2 O, R.sub.7 
R.sub.8 N, R.sub.6 OC(O), R.sub.7 R.sub.8 NC(O), R.sub.9 C(O), R.sub.9 
R.sub.10 R.sub.11 Si, R.sub.9 R.sub.10 R.sub.11 Sn, R.sub.12 R.sub.13 B, 
halogen, R.sub.9 R.sub.10 P(O).sub.q and/or CN, it being possible for the 
composition to comprise, in addition to components (a) and (b), other 
photoinitiators and/or other additives. 
The unsaturated compounds may include one or more olefinic double bonds. 
They may be of low (monomeric) or high (oligomeric) molecular mass. 
Examples of monomers containing a double bond are alkyl or hydroxyalkyl 
acrylates or methacrylates, for example methyl, ethyl, butyl, 2-ethylhexyl 
or 2-hydroxyethyl acrylate, isobornyl acrylate, methyl methacrylate or 
ethyl methacrylate. Silicone acrylates are also advantageous. Other 
examples are acrylonitrile, acrylamide, methacrylamide, N-substituted 
(meth)acrylamides, vinyl esters such as vinyl acetate, vinyl ethers such 
as isobutyl vinyl ether, styrene, alkyl- and halostyrenes, 
N-vinylpyrrolidone, vinyl chloride or vinylidene chloride. 
Examples of monomers containing two or more double bonds are the 
diacrylates of ethylene glycol, propylene glycol, neopentyl glycol, 
hexamethylene glycol or of bisphenol A, and 
4,4'-bis(2-acryl-oyloxyethoxy)diphenylpropane, trimethylolpropane 
triacrylate, pentaerythritol triacrylate or tetraacrylate, vinyl acrylate, 
divinylbenzene, divinyl succinate, diallyl phthalate, triallyl phosphate, 
triallyl isocyanurate or tris(2-acryloylethyl) isocyanurate. 
Examples of polyunsaturated compounds of relatively high molecular mass 
(oligomers) are acrylisized epoxy resins, acrylisized polyesters, 
polyesters containing vinyl ether or epoxy groups, and also polyurethanes 
and polyethers. Further examples of unsaturated oligomers are unsaturated 
polyester resins, which are usually prepared from maleic acid, phthalic 
acid and one or more diols and have molecular weights of from about 500 to 
3000. In addition it is also possible to employ vinyl ether monomers and 
oligomers, and also maleate-terminated oligomers with polyester, 
polyurethane, polyether, polyvinyl ether and epoxy main chains. Of 
particular suitability are combinations of oligomers which carry vinyl 
ether groups and of polymers as described in WO 90/01512. However, 
copolymers of vinyl ether and maleic acid-functionalized monomers are also 
suitable. Unsaturated oligomers of this kind can also be referred to as 
prepolymers. 
Particularly suitable examples are esters of ethylenically unsaturated 
carboxylic acids and polyols or polyepoxides, and polymers having 
ethylenically unsaturated groups in the chain or in side groups, for 
example unsaturated polyesters, polyamides and polyurethanes and 
copolymers thereof, alkyd resins, polybutadiene and butadiene copolymers, 
polyisoprene and isoprene copolymers, polymers and copolymers containing 
(meth)acrylic groups in side chains, and also mixtures of one or more such 
polymers. 
Examples of unsaturated carboxylic acids are acrylic acid, methacrylic 
acid, crotonic acid, itaconic acid, cinnamic acid, and unsaturated fatty 
acids such as linolenic acid or oleic acid. Acrylic and methacrylic acid 
are preferred. 
Suitable polyols are aromatic and, in particular, aliphatic and 
cycloaliphatic polyols. Examples of aromatic polyols are hydroquinone, 
4,4-dihydroxydiphenyl, 2,2-di(4-hydroxyphenyl)propane, and also novolaks 
and resols. Examples of polyepoxides are those based on the abovementioned 
polyols, especially the aromatic polyols, and epichlorohydrin. Other 
suitable polyols are polymers and copolymers containing hydroxyl groups in 
the polymer chain or in side groups, examples being polyvinyl alcohol and 
copolymers thereof or polyhydroxyalkyl methacrylates or copolymers 
thereof. Further polyols which are suitable are oligoesters having 
hydroxyl end groups. 
Examples of aliphatic and cycloaliphatic polyols are alkylenediols having 
preferably 2 to 12 C atoms, such as ethylene glycol, 1,2- or 
1,3-propanediol, 1,2-, 1,3- or 1,4-butanediol, pentanediol, hexanediol, 
octanediol, dodecanediol, diethylene glycol, triethylene glycol, 
polyethylene glycols having molecular weights of preferably from 200 to 
1500, 1,3-cyclopentanediol, 1,2-, 1,3- or 1,4-cyclohexanediol, 
1,4-dihydroxymethylcyclohexane, glycerol, tris(.beta.-hydroxyethyl)amine, 
trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol 
and sorbitol. 
The polyols may be partially or completely esterified with one carboxylic 
acid or with different unsaturated carboxylic acids, and in partial esters 
the free hydroxyl groups may be modified, for example etherified or 
esterified with other carboxylic acids. 
Examples of esters are: 
trimethylolpropane triacrylate, trimethylolethane triacrylate, 
trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, 
tetramethylene glycol dimethacrylate, triethylene glycol dimethacrylate, 
tetraethylene glycol diacrylate, pentaerythritol diacrylate, 
pentaerythritol triacrylate, pentaerythritol tetraacrylate, 
dipentaerythritol diacrylate, dipentaerythritol triacrylate, 
dipentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, 
dipentaerythritol hexaacrylate, tripentaerythritol octaacrylate, 
pentaerythritol dimethacrylate, pentaerythritol trimethacrylate, 
dipentaerythritol dimethacrylate, dipentaerythritol tetramethacrylate, 
tripentaerythritol octamethacrylate, pentaerythritol diitaconate, 
dipentaerythritol trisitaconate, dipentaerythritol pentaitaconate, 
dipentaerythritol hexaitaconate, ethylene glycol diacrylate, 
1,3-butanediol diacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol 
diitaconate, sorbitol triacrylate, sorbitol tetraacrylate, 
pentaerythritol-modified triacrylate, sorbitol tetra methacrylate, 
sorbitol pentaacrylate, sorbitol hexaacrylate, oligoester acrylates and 
methacrylates, glycerol diacrylate and triacrylate, 1,4-cyclohexane 
diacrylate, bisacrylates and bismethacrylates of polyethylene glycol with 
a molecular weight of from 200 to 1500, or mixtures thereof. 
Also suitable as components (a) are the amides of identical or different, 
unsaturated carboxylic acids with aromatic, cycloaliphatic and aliphatic 
polyamines having preferably 2 to 6, especially 2 to 4, amino groups. 
Examples of such polyamines are ethylenediamine, 1,2- or 
1,3-propylenediamine, 1,2-, 1,3- or 1,4-butylenediamine, 
1,5-pentylenediamine, 1,6-hexylenediamine, octylenediamine, 
dodecylenediamine, 1,4-diaminocyclohexane, isophoronediamine, 
phenylenediamine, bisphenylenediamine, di-.beta.-aminoethyl ether, 
diethylenetriamine, triethylenetetramine, di(.beta.-aminoethoxy)- or 
di(.beta.-aminopropoxy)ethane. Other suitable polyamines are polymers and 
copolymers, preferably with additional amino groups in the side chain, and 
oligoamides having amino end groups. Examples of such unsaturated amides 
are methylenebisacrylamide, 1,6-hexamethylenebisacrylamide, 
diethylenetriaminetrismethacrylamide, bis(methacrylamidopropoxy)ethane, 
.beta.-methacrylamidoethyl methacrylate and 
N(.beta.-hydroxyethoxy)ethyl!acrylamide. 
Suitable unsaturated polyesters and polyamides are derived, for example, 
from maleic acid and from diols or diamines. Some of the maleic acid can 
be replaced by other dicarboxylic acids. They can be used together with 
ethylenically unsaturated comonomers, for example styrene. The polyesters 
and polyamides may also be derived from dicarboxylic acids and from 
ethylenically unsaturated diols or diamines, especially from those with 
relatively long chains of, for example 6 to 20 C atoms. Examples of 
polyurethanes are those composed of saturated or unsaturated diisocyanates 
and of unsaturated or, respectively, saturated diols. 
Polybutadiene and polyisoprene and copolymers thereof are known. Examples 
of suitable comonomers are olefins, such as ethylene, propene, butene and 
hexene, (meth)acrylates, acrylonitrile, styrene or vinyl chloride. 
Polymers with (meth)acrylate groups in the side chain are likewise known. 
They may, for example, be reaction products of epoxy resins based on 
novolaks with (meth)acrylic acid, or may be homo- or copolymers of vinyl 
alcohol or hydroxyalkyl derivatives thereof which are esterified with 
(meth)acrylic acid, or may be homo- and copolymers of (meth)acrylates 
which are esterified with hydroxyalkyl (meth)acrylates. 
The photopolymerizable compounds can be used alone or in any desired 
mixtures. It is preferred to use mixtures of polyol (meth)acrylates. 
Binders as well can be added to these novel compositions, and this is 
particularly expedient when the photopolymerizable compounds are liquid or 
viscous substances. The quantity of binder may, for example, be 5-95%, 
preferably 10-90% and especially 40-90%, by weight relative to the overall 
solids content. The choice of binder is made depending on the field of 
application and on properties required for this field, such as the 
capacity for development in aqueous and organic solvent systems, adhesion 
to substrates and sensitivity to oxygen. 
Examples of suitable binders are polymers having a molecular weight of 
about 5000 to 2000000, preferably 10000 to 1000000. Examples are: homo- 
and copolymers of acrylates and methacrylates, for example copolymers of 
methyl methacrylate/ethyl acrylate/methacrylic acid, poly(alkyl 
methacrylates), poly(alkyl acrylates); cellulose esters and cellulose 
ethers, such as cellulose acetate, cellulose acetobutyrate, 
methylcellulose, ethylcellulose; polyvinylbutyral, polyvinylformal, 
cyclized rubber, polyethers such as polyethylene oxide, polypropylene 
oxide and polytetrahydrofuran; polystyrene, polycarbonate, polyurethane, 
chlorinated polyolefins, polyvinyl chloride, vinyl chloride/vinylidene 
copolymers, copolymers of vinylidene chloride with acrylonitrile, methyl 
methacrylate and vinyl acetate, polyvinyl acetate, copoly(ethylenelvinyl 
acetate), polymers such as polycaprolactam and 
poly(hexamethylenadipamide), and polyesters such as poly(ethylene glycol 
terephtalate) and poly(hexamethylene glycol succinate). 
The unsaturated compounds can also be used as a mixture with 
non-photopolymerizable, film-forming components. These may, for example, 
be physically drying polymers or solutions thereof in organic solvents, 
for instance nitrocellulose or cellulose acetobutyrate. They may also, 
however, be chemically and/or thermally curable (heat-curable) resins, 
examples being polyisocyanates, polyepoxides and melamine resins. The use 
of heat-curable resins at the same time is important for use in systems 
known as hybrid systems, which in a first stage are photopolymerized and 
in a second stage are crosslinked by means of thermal aftertreatment. 
The invention additionally provides compositions which in addition to 
components (a) and (b) comprise at least one coinitiator or electron 
acceptor, respectively (c), for example a neutral, cationic or anionic dye 
or a UV absorber. 
Suitable dyes (c) are described above. Other suitable examples are 
benzoxanthene, benzothioxanthene, pyronine or porphyrin dyes. Particularly 
preferred are compositions containing cyanine derivatives as a dye. 
Particularly preferred are cyanines of the formula IV, where n is 1-4, Y 
is C(CH.sub.3).sub.2 or S and R is C.sub.1 -C.sub.10 alkyl. 
Examples of UV absorbers which are suitable as coinitiator or electron 
acceptor, respectively, (c) are thioxanthone derivatives, coumarins, 
benzophenone, benzophenone derivatives or derivatives of 
hexaarylbisimidazole. Examples of suitable hexaarylbisimidazole 
derivatives are described in U.S. Pat. Nos. 3,784,557, 4,252,887, 
4,311,783, 4,459,349, 4,410,621 and 4,622,286. Of particular advantage are 
2-o-chlorophenyl-substituted derivatives, such as 
2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,1'-bisimidazole. Other UV 
absorbers suitable in this context are, for example, polycyclic aromatic 
hydrocarbons, for example anthracene or pyrene, and the triazines 
described in EP-A-137 452, in DE-A-27 18 254 and in DE-A-22 43 621. 
Further suitable triazines can be found in U.S. Pat. No. 4,950,581, column 
14, line 60 to column 18, line 44. Of particular advantage are 
trihalomethyltriazines, for example 
2,4-bis(trichloromethyl)-6-(4-styrylphenyl)-s-triazine. 
Other suitable coinitiators or electron acceptors (c) are 
benzoteridinediones (described in JP Hei 02 113002), substituted 
benzophenones (e.g. Michler's Ketone, Quantacure ABQ, Quantacure BPQ and 
Quantacure BTC from International Biosynthetics), trichloromethyltriazine 
(described in JP Hei 01 033548), metal complexes (described in JP Hei 04 
261405), porphyrins (described in JP Hei 06 202548 and JP Hei 06 195014), 
coumarins and ketocoumarins (described in U.S. Pat. No. 4,950,581 and JP 
Hei 06 175557), p-aminophenyl compounds (described in EP-A 475153), 
xanthenes (described in JP Hei 06 175566) or pyrylium, thiopyrylium and 
selenopyrylium dyes (described in JP Hei 06 175563). 
Also suitable as coinitiators and electron acceptors are readily reducible 
compounds. The term readily reducible compound refers in this context also 
to compounds described in U.S. Pat. No. 4,950,581, including for example 
iodonium salts, sulfonium salts, organic peroxides, compounds containing 
carbon halide bonds (trichloromethyltriazines, heterocyclic sulfur 
compounds and other photoinitiators (.alpha.-amino ketones). Examples of 
other additives are heterocycles as described in the patents and patent 
applications U.S. Pat. No. 5,168,032, JP 02 244050, JP 02 054268, JP 01 
017048 and DE 383308. 
Examples of further additives are aromatic imines described in U.S. Pat. 
No. 5,079,126, and aromatic diazo compounds described in U.S. Pat. No. 
5,200,292 (e.g. iminoquinone diazides), thiols, described in U.S. Pat. No. 
4,937,159 and thiols and N,N-dialkylaniline described in U.S. Pat. No. 
4,874,685. It is also possible to employ two or more of the abovementioned 
coinitiators or electron acceptors and additives in combination. 
As already mentioned, it is advantageous to combine the novel borate 
compounds with coinitiators, inter alia sensitizers (that means energy 
transfer compounds). In this context, additionally and particularly, 
combinations with two or more different sensitizers, for example mixtures 
of the novel borate comopunds with "onium" salts and thioxanthones or 
coumarins or dyes, are highly effective. Preferred "onium" salts in these 
mixtures are diphenyliodonium hexafluorophosphate, 
(p-octyloxyphenyl)-(phenyl)iodonium hexafluorophosphate, or corresponding 
other anions of these compounds, for example the halides; but also 
sulfonium salts, for example triarylsulfonium salts (Cyracure.RTM. UVI 
6990, Cyracure.RTM. UVI-6974 from Union Carbide; Degacure.RTM. KI 85 from 
Degussa or SP-150 und SP-170 from Asahi Denka). Preference is given, for 
example, to a mixture of the novel borate compounds with diphenyliodonium 
hexafluorophosphate and isopropylthioxanthone, to a mixture of the novel 
borate compounds with (p-octyloxyphenyl)(phenyl)iodonium 
hexafluorophosphate and isopropylthioxanthone, and to a mixture of the 
novel borate compounds with 
##STR24## 
(=Cyracure.RTM. UVI-6974) and isopropylthioxanthone. 
However, it is also particularly advantageous to add yet another 
photoinitiator, of the .alpha.-amino ketone type, to the abovementioned 
mixtures. For example, mixtures of the novel borates with onium salts and 
thioxanthones or dyes and .alpha.-amino ketones are highly effective. A 
preferred example is the mixture of the novel borate compounds with 
diphenyliodonium hexafluorophosphate or (p-octylphenyl)(phenyl)iodonium 
hexafluorophosphate, isopropylthioxanthone and 
(4-methylthiobenzoyl)methyl-1-morpholino-ethane. 
The invention also provides a composition comprising in addition to 
components (a) and (b) at least one neutral, anionic or cationic dye or a 
thioxanthone and an onium compound. The invention additionally provides a 
composition of this kind additionally comprising a free-radical 
photoinitiator, especially an .alpha.-amino ketone compound. 
The invention provides, furthermore, a composition comprising in addition 
to components (a) and (b) at least one compound of the formula III 
##STR25## 
in which R.sub.a, R.sub.b, R.sub.c and R.sub.d independently of one 
another are C.sub.1 -C.sub.12 alkyl, trimethylsilylmethyl, phenyl, another 
aromatic hydrocarbon, C.sub.1 -C.sub.6 alkylphenyl, allyl, phenyl-C.sub.1 
-C.sub.6 alkyl, C.sub.2 -C.sub.8 alkenyl, C.sub.2 -C.sub.8 alkynyl, 
C.sub.3 -C.sub.12 cycloalkyl or saturated or unsaturated heterocyclic 
radicals, wherein the radicals phenyl, another aromatic hydrocarbon, 
phenyl-C.sub.1 -C.sub.6 alkyl, or saturated or unsaturated heterocyclic 
radicals are unsubstituted or substituted by 1-5 times by C.sub.1 
-C.sub.20 alkyl, C.sub.2 -C.sub.20 alkyl which is interrupted by one or 
more radicals O, S(O).sub.p or NR.sub.5, or are substituted by OR.sub.6, 
R.sub.6 S(O).sub.p, R.sub.6 S(O).sub.2 O, R.sub.7 R.sub.8 N, R.sub.6 
OC(O), R.sub.7 R.sub.8 NC(O), R.sub.9 C(O), R.sub.9 R.sub.10 R.sub.11 Si, 
R.sub.9 R.sub.10 R.sub.11 Sn, R.sub.12 R.sub.13 B, halogen, R.sub.9 
R.sub.10 P(O).sub.q, and/or CN, 
p is 0, 1 or 2; 
q is 0 or 1; 
R.sub.5 is hydrogen, C.sub.1 -C.sub.12 alkyl, phenyl-C.sub.1 -C.sub.6 alkyl 
or phenyl, where the radicals phenyl-C.sub.1 -C.sub.6 alkyl or phenyl are 
unsubstitued or are substituted 1-5 times by C.sub.1 -C.sub.6 alkyl, 
C.sub.1 -C.sub.12 alkoxy and/or halogen; 
R.sub.6 is C.sub.1 -C.sub.12 alkyl, phenyl-C.sub.1 -C.sub.6 alkyl or 
phenyl, where the radicals phenyl-C.sub.1 -C.sub.6 alkyl or phenyl are 
unsubstituted or are substituted 1-5 times by C.sub.1 -C.sub.6 alkyl, 
C.sub.1 -C.sub.12 alkoxy and/or halogen; 
R.sub.7 and R.sub.8 independently of one another are C.sub.1 -C.sub.12 
alkyl, C.sub.3 -C.sub.12 cycloalkyl, phenyl-C.sub.1 -C.sub.6 alkyl or 
phenyl where the radicals phenyl-C.sub.1 -C.sub.6 alkyl or phenyl are 
unsubstituted or are substituted 1-5 times by C.sub.1 -C.sub.6 alkyl, 
C.sub.1 -C.sub.12 alkoxy, R.sub.6 OC(O), CN and/or halogen or R.sub.7 and 
R.sub.8 together with the N atom to which they are attached, form a 5- or 
6-membered ring which may additionally contain O or S atoms; 
R.sub.9, R.sub.10 and R.sub.11 independently of one another are C.sub.1 
-C.sub.12 alkyl, C.sub.3 -C.sub.12 cycloalkyl, phenyl-C.sub.1 -C.sub.6 
alkyl or phenyl, where the radicals phenyl-C.sub.1 -C.sub.6 alkyl or 
phenyl are unsubstituted or are substituted 1-5-times by C.sub.1 -C.sub.6 
alkyl, C.sub.1 -C.sub.12 alkoxy and/or halogen; 
R.sub.12 and R.sub.13 independently of one another are C.sub.1 -C.sub.12 
alkyl, C.sub.3 -C.sub.12 cycloalkyl, phenyl-C.sub.1 -C.sub.6 alkyl or 
phenyl where the radicals phenyl-C.sub.1 -C.sub.6 alkyl or phenyl are 
unsubstituted or are substituted 1-5 times by C.sub.1 -C.sub.6 alkyl, 
C.sub.1 -C.sub.12 alkoxy and/or halogen, or R.sub.12 and R.sub.13, 
together with the B atom to which they are attached, form a 5- or 
6-membered ring; and 
Z is a radical which is able to form positive ions, especially alkali 
metals, ammonium or tetralkylammonium. 
The definitions of the radicals R.sub.5 -R.sub.13, C.sub.1 -C.sub.12 alkyl, 
trimethylsilylmethyl, phenyl, other aromatic hydrocarbons, C.sub.1 
-C.sub.6 alkylphenyl, allyl, phenyl-C.sub.1 -C.sub.6 alkyl, C.sub.2 
-C.sub.8 alkenyl, C.sub.2 -C.sub.8 alkynyl, C.sub.3 -C.sub.12 cycloalkyl, 
saturated or unsaturated heterocyclic radical, radical which is able to 
form positive ions, alkali metal, ammonium or tetraalkylammonium are as 
indicated above. 
The invention also provides a composition comprising at least one borate of 
the formula I or I' and at least one dye which changes or loses its colour 
during or after the radiation, which dye may also, as cation, be part of 
the compound of the formula I or I'. Examples of such dyes are cyanine 
dyes or pyrylium dyes. 
In addition to the photoinitiator the photopolymerizable mixtures may 
include various additives. Examples of these are thermal inhibitors, which 
are intended to prevent premature polymerization, examples being 
hydroquinone, hydroquinine derivatives, p-methoxyphenol, .beta.-naphthol 
or sterically hindered phenols, such as 2,6-di-tert-butyl-p-cresol. In 
order to increase the stability on storage in the dark it is possible, for 
example, to use copper compounds, such as copper naphthenate, stearate or 
octoate, phosphorus compounds, for example triphenylphosphine, 
tributylphosphine, triethyl phosphite, triphenyl phosphite or tribenzyl 
phosphite, quaternary ammonium compounds, for example tetramethylammonium 
chloride or trimethylbenzylammonium chloride, or hydroxylamine 
derivatives, for example N-diethylhydroxylamine. To exclude atmospheric 
oxygen during the polymerization it is possible to add paraffin or similar 
wax-like substances which, being of inadequate solubility in the polymer, 
migrate to the surface in the beginning of polymerization and form a 
transparent surface layer which prevents the ingress of air. It is also 
possible to apply an oxygen-impermeable layer. Light stabilizers which can 
be added in a small quantity are UV absorbers, for example those of the 
hydroxyphenylbenzotriazole, hydroxyphenyl-benzophenone, oxalamide or 
hydroxyphenyl-s-triazine type. These compounds can be used individually or 
in mixtures, with or without sterically hindered amines (HALS). 
Examples of such UV absorbers and light stabilizers are 
1. 2-(2'-hydroxyphenyl)benzotriazoles for example 
2-(2'-hydroxy-5'-methylphenyl)-benzotriazole, 
2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)benzotriazole, 
2-(5'-tert-butyl-2'-hydroxyphenyl)benzotriazole, 
2-(2'-hydroxy-5'-(1,1,3,3-tetramethylbutyl)phenyl)-benzotriazole, 
2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)-5-chlorobenzotriazole, 
2-(3'-tert-butyl-2'-hydroxy-5'-methylphenyl)-5-chlorobenzotriazole, 
2-(3'-sec-butyl-5'-tert-butyl-2'-hydroxyphenyl)benzotrizole, 
2-(2'-hydroxy-4'-octoxyphenyl)benzotriazole, 
2-(3',5'di-tert-amyl-2'-hydroxyphenyl)benzotriazole, 
2-(3',5'-bis-(.alpha.,.alpha.-dimethylbenzyl)-2'-hydroxyphenyl)-benzotriaz 
ole, mixture of 
2-(3'-tert-butyl-2'-hydroxy-5'-(2-octyloxycarbonylethyl)phenyl)-5-chlorobe 
nzotriazole, 
2-(3'-tert-butyl-5'-2-(2-ethyl-hexyloxy)carbonylethyl!-2'-hydroxyphenyl)- 
5-chlorobenzotriazole, 
2-(3'-tert-butyl-2'-hydroxy-5'-(2-methoxycarbonylethyl)phenyl)-5-chloroben 
zotriazole, 
2-(3'-tert-butyl-2'-hydroxy-5'-(2-methoxycarbonylethyl)phenyl)benzotriazol 
e, 
2-(3'-tert-butyl-2'-hydroxy-5'-(2-octyloxycarbonylethyl)phenyl)benzotriazo 
le, 
2-(3'-tert-butyl-5'-2-(2-ethylhexyloxy)carbonylethyl!-2'-hydroxyphenyl)be 
nzotriazole, 2-(3'-dodecyl-2'-hydroxy-5'-methylphenyl)benzotriazole, and 
2-(3'-tert-butyl-2'-hydroxy-5'-(2-isooctyloxycarbonylethyl)phenylbenzotria 
zole, 
2,2'-methylenebis4-(1,1,3,3-tetramethylbutyl)-6-benzotriazol-2-yl-phenol! 
; transesterification product of 
2-3'-tert-butyl-5'-(2-methoxycarbonylethyl)-2'-hydroxy-phenyl!-benzotriaz 
ole with polyethylene glycol 300; R--CH.sub.2 CH.sub.2 
--COO(CH.sub.2).sub.3 !.sub.2 -- where 
R=3'-tert-butyl-4'-hydroxy-5'-2H-benzotriazol-2-yl-phenyl. 
2. 2-Hydroxybenzophenones, for example the 4-hydroxy-, 4-methoxy-, 
4-octoxy-, 4-decyloxy-, 4-dodecyloxy-, 4-benzyloxy-, 4,2',4'-trihydroxy- 
and 2'-hydroxy-4,4'-dimethoxy derivative. 
3. Esters of substituted or unsubstituted benzoicacids, for example 
4-tert-butylphenyl salicylate, phenyl salicylate, octylphenyl salicylate, 
dibenzoylresorcinol, bis(4-tert-butylbenzoyl)resorcinol, 
benzoylresorcinol, 2,4-di-tert-butylphenyl 
3,5-di-tert-butyl-4-hydroxybenzoate, hexadecyl 
3,5-di-tert-butyl-4-hydroxybenzoate, octadecyl 
3,5-di-tert-butyl-4-hydroxybenzoate, and 2-methyl-4,6-di-tert-butylphenyl 
3,5-di-tert-butyl-4-hydroxybenzoate. 
4. Acrylates, for example isooctyl or ethyl 
.alpha.-cyano-.beta.,.beta.-diphenyl acrylate, methyl 
.alpha.-carbomethoxycinnamate, butyl or methyl 
.alpha.-cyano-.beta.-methyl-p-methoxycinnamate, methyl 
.alpha.-carboxymethoxy-p-methoxycinnamate and 
N-(.beta.-carbomethoxy-.beta.-cyanovinyl)-2-methylindoline. 
5. Sterically hindered amines, for example 
bis-(2,2,6,6-tetramethylpiperidyl) sebacate, 
bis-(2,2,6,6-tetramethylpiperidyl) succinate, 
bis-(1,2,2,6,6-pentamethylpiperidyl) sebacate, 
bis(1,2,2,6,6-pentamethylpiperidyl) 
n-butyl-3,5-di-tert-butyl-4-hydroxybenzylmalonate, condensation product of 
1-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxypiperidine and succinic acid, 
condensation product of 
N,N'-bis-(2,2,6,6-tetramethyl-4-piperidyl)hexamethylenediamine and 
4-tert-octylamino-2,6-dichloro-1,3,5-s-triazine, 
tris-(2,2,6,6-tetramethyl-4-piperidyl) nitrilotriacetate, 
tetrakis-(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butane tetraoate, 
1,1'-(1,2-ethandiyl)bis(3,3,5,5-tetramethyl-piperazinone), 
4-benzoyl-2,2,6,6-tetramethylpiperidine, 
4-stearyloxy-2,2,6,6-tetramethylpiperidine, 
bis-(1,2,2,6,6-pentamethylpiperidyl) 
2-n-butyl-2-(2-hydroxy-3,5-di-tert-butylbenzyl) malonate, 
3-n-octyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro-4.5!decane-2,4-dione, 
bis-(1-octyloxy-2,2,6,6-tetramethylpiperidyl) sebacate, 
bis-(1-octyloxy-2,2,6,6-tetramethylpiperidyl) succinate, condensation 
product of N,N'-bis-(2,2,6,6-tetra-methyl-4-piperidyl)hexamethylenediamine 
and 4-morpholino-2,6-dichloro-1,3,5-triazine, condensation product of 
2-chloro-4,6-di-(4-n-butylamino-2,2,6,6-tetramethylpiperidyl)-1,3,5-triazi 
ne and 1,2-bis-(3-aminopropylamino)ethane, condensation product of 
2-chloro-4,6-di-(4-n-butylamino-1,2,2,6,6-pentamethylpiperidyl)-1,3,5-tria 
zine and 1,2-bis-(3-aminopropylamino)ethane, 
8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro4.5!decane-2,4-di 
one, 3-dodecyl-1-(2,2,6,6-tetramethyl-4-piperidyl)pyrrolidine-2,5-dione and 
3-dodecyl-1-(1,2,2,6,6-penta-methyl-4-piperidyl)-pyrrolidine-2,5-dione. 
6. Oxalamides, for example 4,4'-dioctyloxyoxanilide, 
2,2'-diethoxyoxanilide, 2,2'-dioctyloxy-5,5'-di-tert-butyloxanilide, 
2,2'-didodecyloxy-5,5'di-tert-butyloxanilide, 2-ethoxy-2'-ethyl-oxanilide, 
N,N'-bis-(3-dimethylaminopropyl)oxalamide, 
2-ethoxy-5-tert-butyl-2'-ethyloxanilide and its mixture with 
2-ethoxy-2'-ethyl-5,4'-di-tert-butyloxanilide, mixtures of o- and 
p-methoxy- and of o- and p-ethoxy-disubstituted oxanalides. 
7. 2-(2-Hydroxyphenyl)-1,3,5-triazines, for example 
2,4,6-tris(2-hydroxy-4-octyloxyphenyl)-1,3,5-triazine, 
2-(2-hydroxy-4-octyloxyphenyl)-4,6-bis-(2,4-dimethylphenyl)-1,3,5-triazine 
, 2-(2,4-dihydroxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazine, 
2,4-bis(2-hydroxy-4-propyloxy-phenyl)-6-(2,4-dimethylphenyl)-1,3,5-triazin 
e, 2-(2-hydroxy-4-octyloxyphenyl)4,6-bis(4-methylphenyl)-1,3,5-triazine, 
2-(2-hydroxy-4-dodecyloxyphenyl)-4,6-bis(2,4-dimethylphenyl)-1,3,5-triazin 
e, 
2-2-hydroxy-4-(2-hydroxy-3-butyloxy-propyloxy)phenyl!-4,6-bis(2,4-dimethy 
lphenyl)-1,3,5-triazine, 
2-2-hydroxy-4-(2-hydroxy-3-octyloxypropyloxy)phenyl!-4,6-bis(2,4-dimethyl 
phenyl)-1,3,5-triazine, 
2-4-dodecyl/tridecyl-oxy-(2-hydroxypropyl)oxy-2-hydroxy-phenyl!-4,6-bis(2 
,4-dimethylphenyl)-1,3,5-triazine. 
8. Phosphites and phosphonites, for example triphenyl phosphite, diphenyl 
alkyl phosphites, phenyl dialkyl phosphites, tris(nonylphenyl) phosphite, 
trilauryl phosphite, trioctadecyl phosphite, distearyl pentaerythrityl 
diphosphite, tris-(2,4-di-tert-butylphenyl) phosphite, diisodecyl 
pentaerythrityl diphosphite, bis-(2,4-di-tert-butylphenyl) pentaerythrityl 
diphosphite, bis-(2,6-di-tert-butyl-4-methylphenyl) pentaerythrityl 
diphosphite, bis-isodecyloxy pentaerythrityl diphosphite, 
bis-(2,4-di-tert-butyl-6-methylphenyl) pentaerythrityl diphosphite, 
bis-(2,4,6-tri-tert-butylphenyl) pentaerythrityl diphosphite, tristearyl 
sorbityl triphosphite, tetrakis-(2,4-di-tert-butylphenyl)-4,4'-biphenylene 
diphosphonite, 
6-isooctyloxy-2,4,8,10-tetra-tert-butyl-12H-dibenzod,g!-1,3,2-dioxaphosph 
ocine, 
6-fluoro-2,4,8,10-tetra-tert-butyl-12-methyl-dibenzod,g!-1,3,2-dioxaphosp 
hocine, bis-(2,4-di-tert-butyl-6-methylphenyl) methyl phosphite and 
bis(2,4-di-tert-butyl-6-methylphenyl) ethyl phosphite. 
To accelerate the photopolymerization it is possible to add amines, for 
example triethanolamine, N-methyldiethanolamine, p-dimethylaminobenzoate 
or Michler's ketone. The action of the amines can be intensified by the 
addition of aromatic ketones of the benzophenone type. Examples of amines 
which can be used as oxygen scavengers are substituted 
N,N-dialkylanilines, as are described in EP-A-339 841. Other accelerators, 
coinitiators and autoxidizers are thiols, thioethers, disulfides, 
phosphonium salts, phosphine oxides or phosphines, as described, for 
example, in EP-A-438 123, in GB-A-2 180 358 and in JP-A Hei 6 268309. 
Photopolymerization can also be accelerated by adding further 
photosentisizers which shift or broaden the spectral sensitivity. These 
are, in particular, aromatic carbonyl compounds, for example benzophenone, 
thioxanthone, anthraquinone and 3-acylcoumarin derivatives, and also 
3-(aroylmethylene)thiazolines, but also eosine, rhodamine and erythrosine 
dyes. 
The curing process can be assisted by, in particular, compositions which 
are pigmented (for example with titanium dioxide), and also by adding a 
component which under thermal conditions forms free radicals, for example 
an azo compound such as 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 
a triazene, diazo sulfide, pentazadiene or a peroxy compound, for instance 
a hydroperoxide or peroxycarbonate, for example t-butyl hydroperoxide, as 
described for example in EP-A-245 639. 
Further customary additives, depending on the intended use, are fluorescent 
whiteners, fillers, pigments, dyes, wetting agents or levelling 
assistants. 
In order to cure thick and pigmented coatings it is appropriate to add 
glass microspheres or pulverized glass fibres, as described for example in 
U.S. Pat. No. 5,013,768. 
The invention also provides compositions comprising as component (a) at 
least one ethylenically unsaturated photopolymerizable compound which is 
emulsified or dissolved in water. 
Many variants of such radiation-curable aqueous prepolymer dispersions are 
commercially available. A prepolymer dispersion is understood as being a 
dispersion of water and at least one prepolymer dispersed therein. The 
concentration of water in these systems is, for example, from 5 to 80% by 
weight, in particular from 30 to 60% by weight. The concentration of the 
radiation-curable prepolymer or prepolymer mixture is, for example, from 
95 to 20% by weight, in particular from 70 to 40% by weight. In these 
compositions the sum of the percentages given for water and prepolymer is 
in each case 100, with auxiliaries and additives being added in varying 
quantities depending on the intended use. 
The radiation-curable, film-forming prepolymers which are dispersed in 
water and are often also dissolved are aqueous prepolymer dispersions of 
mono- or polyfunctional, ethylenically unsaturated prepolymers which are 
known per se, can be initiated by free radicals and have for example a 
content of from 0.01 to 1.0 mol of polymerizable double bonds per 100 g of 
prepolymer and an average molecular weight of, for example, at least 400, 
in particular from 500 to 10 000. Prepolymers with higher molecular 
weights, however, may also be considered depending on the intended 
application. Use is made, for example, of polyesters containing 
polymerizable C--C double bonds and having an acid number of not more than 
10, of polyethers containing polymerizable C--C double bonds, of 
hydroxyl-containing reaction products of a polyepoxide, containing at 
least two epoxide groups per molecule, with at least one 
.alpha.,.beta.-ethylenically unsaturated carboxylic acid, of polyurethane 
(meth)acrylates and of acrylic copolymers which contain 
.alpha.,.beta.-ethylenically unsaturated acrylic radicals, as are 
described in EP-A-12 339. Mixtures of these prepolymers can likewise be 
used. Also suitable are the polymerizable prepolymers described in EP-A-33 
896, which are thioether adducts of polymerizable prepolymers having an 
average molecular weight of at least 600, a carboxyl group content of from 
0.2 to 15% and a content of from 0.01 to 0.8 mol of polymerizable C-C 
double bonds per 100 g of prepolymer. Other suitable aqueous dispersions, 
based on specific alkyl (meth)acrylate polymers, are described in EP-A-41 
125, and suitable water-dispersible, radiation-curable prepolymers of 
urethane acrylates can be found in DE-A-29 36 039. 
Further additives which may be included in these radiation-curable aqueous 
prepolymer dispersions are dispersion auxiliaries, emulsifiers, 
antioxidants, light stabilizers, dyes, pigments, fillers, for example 
talc, gypsum, silicic acid, rutile, carbon black, zinc oxide, iron oxides, 
reaction accelerators, levelling agents, lubricants, wetting agents, 
thickeners, flatting agents, antifoams and other auxiliaries customary in 
paint technology. Suitable dispersion auxiliaries are water-soluble 
organic compounds which are of high molecular mass and contain polar 
groups, examples being polyvinyl alcohols, polyvinylpyrrolidone or 
cellulose ethers. Emulsifiers which can be used are nonionic emulsifiers 
and, if desired, ionic emulsifiers as well. 
In certain cases it may be of advantage to use mixures of two or more of 
the novel photoinitiators. It is of course also possible to use mixtures 
with known photoinitiators, for example mixtures with benzophenone, 
acetophenone derivatives, for example .alpha.-hydroxycycloalkyl phenyl 
ketones, dialkoxyacetophenones, .alpha.-hydroxy- or 
.alpha.-aminoacetophenones, 4-aroyl-1,3-dioxolanes, benzoin alkyl ethers 
and benzil ketals, monoacyl phosphine oxides, bisacylphosphine oxides, 
titanocenes, ferrocenes, anthraquinone, thioxanthones or xanthones. 
Examples of particularly suitable photoinitiators are: 
1-(4-dodecylbenzoyl)-1-hydroxy-1-methylethane, 
1-(4-isopropylbenzoyl)-1-hydroxy-1-methylethane, 
1-benzoyl-1-hydroxy-1-methylethane, 
1-4(2-hydroxyethoxy)-benzoyl!-1-hydroxy-1-methylethane, 
1-4(acryloyloxyethoxy)benzoyl!-1-hydroxy-1-methylethane, diphenyl ketone, 
penyl-1-hydroxycyclohexyl ketone, 
(4-morpholinobenzoyl)-1-benzyl-1-dimethylaminopropane, 
1-(3,4-di-methoxyphenyl)-2-benzyl-2-dimethylamino-butan-1-one, 
(4-methylthiobenzoyl)-1-methyl-1-morpholinoethane, benzil dimethyl ketal, 
bis(cyclopentadienyl)-bis(2,6-difluoro-3-pyrrylphenyl)titanium, 
cyclopentadienyl-arene-iron(II) complex salts, for example (.eta..sup.6 
-isopropylbenzene)(.eta..sup.5 -cyclopentadienyl)iron(II) 
hexafluorophosphate, trimethylbenzoyldiphenylphosphine oxide, 
bis(2,6-dimethoxy-benzoyl)-(2,4,4-trimethyl-pentyl)phosphine oxide, 
bis(2,4,6-trimethylbenzoyl)-2,4-dipentoxyphenylphosphine oxide or 
bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide. Other suitable 
additional photoinitiators can be found in U.S. Pat. No. 4,950,581 column 
20, line 35 to column 21, line 35. Where the novel photoinitiators are 
employed in hybrid systems, use is made, in addition to the novel 
free-radical hardeners, of cationic photoinitiators, for example peroxide 
compounds, such as benzoyl peroxide (other suitable peroxides are 
described in U.S. Pat. No. 4,950,581 column 19, lines 17-25), aromatic 
sulfonium or iodonium salts as described for example in U.S. Pat. No. 
4,950,581, column 18, line 60 to column 19, line 10 or 
cyclopentadienyl-arene-iron(II) complex salts, for example (.eta..sup.6 
-Iso-propylbenzol)(.eta..sup.5 -cyclopentadien-yl)iron(II) 
hexafluorophosphate. 
The invention therefore further provides compositions which in addition to 
the photoinitiator (b) also comprise at least one further photoinitiator 
(d) and/or other additives and/or coinitiators. 
The photopolymerizable compositions include the photoinitiator (b) or the 
photoinitiators (b) and (d) expediently in a quantity of from 0.05 to 15% 
by weight, preferably from 0.1 to 5% by weight, based on the composition. 
(The quantity indicated relates to the overall quantity of photoinitiator 
in the composition.) 
Compositions comprising as photoinitiator (d) a titanocene, a ferrocene, a 
benzophenone, a benzoin alkyl ether, a benzil ketal, a 
4-aroyl-1,3-dioxolane, a dialkoxyacetophenone, an .alpha.-hydroxy- or 
.alpha.-aminoacetophenone, an .alpha.-hydroxycycloalkyl phenyl ketone, a 
xanthone, a thioxanthone, an anthraquinone or a mono- or bisacylphosphine 
oxide, or mixtures thereof, as additional photoinitiator are of particular 
preference. 
The photopolymerizable compositions can be used for various purposes, for 
example as printing ink, as a clear finish, as a white finish, for example 
for wood or metal, as a coating material, inter alia for paper, wood, 
metal or plastic, as a daylight-curable coating for the marking of 
buildings and roadmarking, for photographic reproduction techniques, for 
holographic recording materials, for image recording techniques or to 
produce printing plates which can be developed with organic solvents or 
with aqueous alkalis, for producing masks for screen printing, as dental 
filling compositions, as adhesives, as pressure-sensitive adhesives, as 
laminating resins, as etch resists or permanent resists, and as solder 
masks for electronic circuits, for producing three-dimensional articles by 
mass curing (UV curing in transparent moulds) or by the stereolithography 
technique, as is described, for example, in U.S. Pat. No. 4,575,330, to 
produce composite materials (for example styrenic polyesters, which may, 
if desired, contain glass fibres and other auxiliaries) and other 
thick-layered compositions, for coating or sealing electronic components, 
or as coatings for optical fibres. 
The novel compounds may additionally be employed as initiators for emulsion 
polymerizations, as polymerization initiators for fixing ordered states of 
liquid-crystalline monomers and oligomers, or as initiators for fixing 
dyes on organic materials. 
In coating materials, use is frequently made of mixtures of a prepolymer 
with polyunsaturated monomers, which may additionally include a 
monounsaturated monomer as well. It is the prepolymer here which primarily 
dictates the properties of the coating film, and by varying it the skilled 
worker is able to influence the properties of the cured film. The 
polyunsaturated monomer functions as a crosslinking agent which renders 
the film insoluble. The monounsaturated monomer functions as a reactive 
diluent, which is used to reduce the viscosity without the need to employ 
a solvent. 
Unsaturated polyester resins are usually used in two-component systems 
together with a monounsaturated monomer, preferably with styrene. For 
photoresists, specific one-component systems are often used, for example 
polymaleimides, polychalcones or polyimides, as described in DE-A-23 08 
830. 
The novel compounds and mixtures thereof can also be used as free-radical 
photoinitiators or photoinitiating systems for radiation-curable powder 
coatings. The powder coatings can be based on solid resins and monomers 
containing reactive double bonds, for example maleates, vinyl ethers, 
acrylates, acrylamides and mixtures thereof. A free-radically UV-curable 
powder coating can be formulated by mixing unsaturated polyester resins 
with solid acrylamides (for example methyl methylacrylamidoglycolate) and 
a novel free-radical photoinitiator, such formulations being as described, 
for example, in the paper "Radiation Curing of Powder Coating", Conference 
Proceedings, Radtech Europe 1993 by M. Wittig and Th. Gohmann. The powder 
coatings can also contain binders, as are described, for example, in 
DE-A-42 28 514 and in EP-A-636 669. Free-radically UV-curable powder 
coatings can also be formulated by mixing unsaturated polyester resins 
with solid acrylates, methacrylates or vinyl ethers and with a novel 
photoinitiator (or photoinitiator mixture). The powder coatings may also 
comprise binders as are described, for example, in DE-A-42 28 514 and in 
EP-A-636 669. The UV-curable powder coatings may additionally comprise 
white or coloured pigments. For example, preferably rutiletitanium dioxide 
can be employed in concentrations of up to 50% by weight in order to give 
a cured powder coating of good hiding power. The procedure normally 
comprises electrostatic or tribostatic spraying of the powder onto the 
substrate, for example metal or wood, melting of the powder by heating, 
and, after a smooth film has formed, radiation-curing of the coating with 
ultraviolet and/or visible light, using for example medium-pressure 
mercury lamps, metal halide lamps or xenon lamps. A particular advantage 
of the radiation-curable powder coatings over their heat-curable 
counterparts is that the flow time after melting the powder particles can 
be delayed in order to ensure the formation of a smooth, high-gloss 
coating. In contrast to heat-curable systems, radiation-curable powder 
coatings can be formulated to melt at lower temperatures without the 
unwanted effect of shortening their lifetime. For this reason, they are 
also suitable as coatings for heat-sensitive substrates, for example wood 
or plastics. In addition to the novel photoinitiators, the powder coating 
formulations may also include UV absorbers. Appropriate examples are 
listed above in sections 1.-8. 
The novel photocurable compositions are suitable, for example, as coating 
materials for substrates of all kinds, for example wood, textiles, paper, 
ceramics, glass, plastics such as polyesters, polyethylene terephthalate, 
polyolefins or cellulose acetate, especially in the form of films, and 
also metals such as Al, Cu, Ni, Fe, Zn, Mg or Co and GaAs, Si or SiO.sub.2 
to which it is intended to apply a protective layer or, by means of 
imagewise exposure, to generate an image. 
Coating of the substrates can be carried out by applying to the substrate a 
liquid composition, a solution or a suspension. The choice of solvents and 
the concentration depend principally on the type of composition and on the 
coating technique. The solvent should be inert, i.e. it should not undergo 
a chemical reaction with the components and should be able to be removed 
again, after coating, in the course of drying. Examples of suitable 
solvents are ketones, ethers and esters, such as methyl ethyl ketone, 
isobutyl methyl ketone, cyclopentanone, cyclohexanone, 
N-methylpyrrolidone, dioxane, tetrahydrofuran, 2-methoxyethanol, 
2-ethoxyethanol, 1-methoxy-2-propanol, 1,2-dimethoxyethane, ethyl acetate, 
n-butyl acetate and ethyl 3-ethoxypropionate. The solution is applied 
uniformly to a substrate by means of known coating techniques, for example 
by spin coating, dip coating, knife coating, curtain coating, brushing, 
spraying, especially by electrostatic spraying, and reverse-roll coating, 
and also by means of electrophoretic deposition. It is also possible to 
apply the photosensitive layer to a temporary, flexible support and then 
to coat the final substrate, for example a copper-clad circuit board, by 
transferring the layer via lamination. 
The quantity applied (coat thickness) and the nature of the substrate 
(layer support) are dependent on the desired field of application. The 
range of coat thicknesses generally comprises values from about 0.1 .mu.m 
to more than 100 .mu.m. 
The novel radiation-sensitive compositions find application as negative 
resists, having a very high sensitivity to light and being able to be 
developed in an aqueous alkaline medium without swelling. They are 
suitable as photoresists for electronics (electroplating resist, etch 
resist, solder resist), the production of printing plates, such as offset 
printing plates or screen printing plates, for use in chemical milling or 
as a microresist in the production of integrated circuits. The possible 
layer supports, and the processing conditions of the coating substrates, 
are just as varied. 
The compounds according to the invention also find application for the 
production of one- or more-layered materials for the image recording ore 
image reproduction (copies, reprography), which may be uni- or 
polychromatic. Furthermore the materials are suitable for colour proofing 
systems. In this technology formulations containing microcapsules can be 
applied and for the image production the radiation curing can be followed 
by a thermal treatment. Such systems and technologies and their 
applications are for example disclosed in U.S. Pat. No. 5,376,459. 
Substrates used for photographic information recordings include, for 
example, films of polyester, cellulose acetate or polymer-coated papers; 
substrates for offset printing formes are specially treated aluminium, 
substrates for producing printed circuits are copper-clad laminates, and 
substrates for producing integrated circuits are silicon wafers. The layer 
thicknesses for photographic materials and offset printing formes is 
generally from about 0.5 .mu.m to 10 .mu.m, while for printed circuits it 
is from 1.0 .mu.m to about 100 .mu.m. 
Following the coating of the substrates, the solvent is removed, generally 
by drying, to leave a coat of the photoresist on the substrate. 
The term "imagewise" exposure includes both exposure through a photomask 
comprising a predetermined pattern, for example a slide, exposure by means 
of a laser beam, which for example is moved under computer control over 
the surface of the coated substrate and in this way produces an image, and 
irradiation with computer-controlled electron beams. 
Following the imagewise exposure of the material and prior to development, 
it may be advantageous to carry out thermal treatment for a short time. In 
this case only the exposed sections are thermally cured. The temperatures 
employed are generally 50-150.degree. C., preferably 80-130.degree. C.; 
the period of thermal treatment is in general between 0.25 and 10 minutes. 
The photocurable composition may additionally be used in a process for 
producing printing plates or photoresists as is described, for example, in 
DE-A-40 13 358. In such a process the composition is exposed for a short 
time to visible light with a wavelength of at least 400 nm, without a 
mask, prior to, simultaneously with or following imagewise irradiation. 
After the exposure and, if implemented, thermal treatment, the unexposed 
areas of the photosensitive coating are removed with a developer in a 
manner known per se. 
As already mentioned, the novel compositions can be developed by aqueous 
alkalis. Particularly suitable aqueous-alkaline developer solutions are 
aqueous solutions of tetraalkylammonium hydroxides or of alkali metal 
silicates, phosphates, hydroxides and carbonates. Minor quantities of 
wetting agents and/or organic solvents may also be added, if desired, to 
these solutions. Examples of typical organic solvents, which may be added 
to the developer liquids in small quantities, are cyclohexanone, 
2-ethoxyethanol, toluene, acetone and mixtures of such solvents. 
Photocuring is of great importance for printings, since the drying time of 
the binder is a critical factor for the production rate of graphic 
products, and should be in the order of fractions of seconds. UV-curable 
inks are particularly important for screen printing. 
As already mentioned above, the novel mixtures are highly suitable also for 
producing printing plates. This application uses, for example, mixtures of 
soluble linear polyamides or styrene/butadiene and/or styrene/isoprene 
rubber, polyacrylates or polymethyl methacrylates containing carboxyl 
groups, polyvinyl alcohols or urethane acrylates with photopolymerizable 
monomers, for example acrylamides and/or methacrylamides, or acrylates 
and/or methacrylates, and a photoinitiator. Films and plates of these 
systems (wet or dry) are exposed over the negative (or positive) of the 
printed original, and the uncured parts are subsequently washed out using 
an appropriate solvent. 
Another field where photocuring is employed is the coating of metals, in 
the case, for example, of the coating of metal plates and tubes, cans or 
bottle caps, and the photocuring of polymer coatings, for example of floor 
or wall coverings based on PVC. 
Examples of the photocuring of paper coatings are the colourless varnishing 
of labels, record sleeves and book covers. 
Also of interest is the use of the novel compounds for curing shaped 
articles made from composite compositions. The composite compound consists 
of a self-supporting matrix material, for example a glass fibre fabric, or 
alternatively, for example, plant fibres cf. K.-P. Mieck, T. Reussmann in 
Kunststoffe 85 (1995), 366-3701!, which is impregnated with the 
photocuring formulation. Shaped parts comprising composite compounds, when 
produced using the novel compounds, attain a high level of mechanical 
stability and resistance. The novel compounds can also be employed as 
photocuring agents in moulding, impregnating and coating compositions as 
are described, for example, in EP-A-7086. Examples of such compositions 
are gel coat resins, which are subject to stringent requirements regarding 
curing activity and yellowing resistance, and fibre-reinforced mouldings, 
for example, light diffusing panels which are planar or have lengthwise or 
crosswise corrugation. Techniques for producing such mouldings, such as 
hand lay-up, spray lay-up, centrifugal casting or filament winding, are 
described, for example, by P. H. Selden in "Glasfaserverstarkte 
Kunststoffe", page 610, Springer Verlag Berlin-Heidelberg-New York 1967. 
Examples of articles which can be produced by these techniques are boats, 
fibre board or chipboard panels with a double-sided coating of glass 
fibre-reinforced plastic, pipes, containers, etc. Further examples of 
moulding, impregnating and coating compositions are UP resin gel coats for 
mouldings containing glass fibres (GRP), such as corrugated sheets and 
paper laminates. Paper laminates may be based on urea resins or melamine 
resins. Prior to production of the laminate, the gel coat is produced on a 
support (for example a film). The novel photocurable compositions can also 
be used for casting resins or for embedding articles, for example 
electronic components, etc. Curing is carried out using medium-pressure 
mercury lamps as are conventional in UV curing. However, there is also 
particular interest in less intense lamps, for example of the type TL 
40W/03 or TL40W/05. The intensity of these lamps corresponds approximately 
to that of sunlight. It is also possible to use direct sunlight for 
curing. A further advantage is that the composite composition can be 
removed from the light source in a partly cured, plastic state and can be 
shaped, with full curing taking place subsequently. 
The compositions and compounds according to the invention can be used for 
the production of waveguides, optical switches wherein advantage is taken 
of the development of a difference in the index of refraction between 
irradiated and unirradiated areas. 
The use of photocurable compositions for imaging techniques and for the 
optical production of information carriers is also important. In such 
applications, as already described above, the layer (wet or dry) applied 
to the support is irradiated through a photomask with UV or visible light, 
and the unexposed areas of the layer are removed by treatment with a 
solvent (=developer). Application of the photocurable layer to metal can 
also be carried out by electrodeposition. The exposed areas are polymeric 
through crosslinking and are therefore insoluble and remain on the 
support. Appropriate colouration produces visible images. Where the 
support is a metallized layer, the metal can, following exposure and 
development, be etched away at the unexposed areas or reinforced by 
electroplating. In this way it is possible to produce electronic circuits 
and photoresists. 
The photosensitivity of the novel compositions extends in general from 
about 200 nm through the UV region into the infrared region (about 20000 
.mu.m, in particular 1200 nm) and therefore spans a very broad range. 
Suitable radiation is present, for example, in sunlight or light from 
artificial light sources. Consequently, a large number of very different 
types of light sources are employed. Both point sources and arrays ("lamp 
carpets") are suitable. Examples are carbon arc lamps, xenon arc lamps, 
medium-, high- and low-pressure mercury lamps, possibly with metal halide 
dopes (metal-halogen lamps), microwave-stimulated metal vapour lamps, 
excimer lamps, superactinic fluorescent tubes, fluorescent lamps, argon 
incandescent lamps, electronic flashlights, photographic flood lamps, 
electron beams and X-rays, produced by means of synchrotrons or laser 
plasma. The distance between the lamp and the substrate to be exposed in 
accordance with the invention may vary depending on the intended 
application and the type and output of lamp, and may be, for example, from 
2 cm to 150 cm. Laser light sources, for example excimer lasers, such as 
krypton F lasers for exposure at 248 nm. are especially suitable. Lasers 
in the visible region and in the IR region can also be employed. In this 
case, the high sensitivity of the novel materials is very advantageous. By 
this method it is possible to produce printed circuits in the electronics 
industry, lithographic offset printing plates or relief printing plates, 
and also photographic image recording materials. 
The invention therefore also provides a process for the photopolymerization 
of nonvolatile monomeric, oligomeric or polymeric compounds containing at 
least one ethylenically unsaturated double bond, which comprises adding to 
the abovementioned compounds at least one compound of the formula I 
according to claim 1 in which G is a dye radical, or at least one compound 
of the formula I or I' according to claim 1 in combination with an 
electron acceptor and irradiating the mixture with light from the infrared 
region through the UV region to a wavelength of 200 nm. 
The invention additionally provides for the use of the above-described 
composition for preparing pigmented and unpigmented coatings, printing 
inks, powder coatings, printing plates, adhesives, dental compositions, 
waveguides, optical switches, colour proofing systems, glass fibre cable 
coatings, screen printing stencils, resist materials, materials for 
encapsulating electrical and electronic components, for photographical 
reproductions, for producing composites, for producing magnetic recording 
materials, for producing three-dimensional objects by stereolithography 
and as image recording material, especially for holographic recordings. 
The invention additionally provides a coated substrate which is coated on 
at least one surface with a composition as described above, and describes 
a process for the photographic production of relief images, in which a 
coated substrate is subjected to imagewise exposure and then the unexposed 
portions are removed with a solvent. Of particular advantage in this 
context is the laser beam exposure already mentioned above. 
The novel compounds of the formulae I and I' are white powders which are 
stable in air. As already mentioned above, in the compounds at least two 
aryl radicals are substituted in at least one o-position of the aryl ring. 
These compounds surprisingly reveal an extremely good reactivity as 
free-radical photoinitiators. 
Those compounds of the formulae I and I' which contain electron-attracting 
groups are in general also acid-stable and can be employed in acidic 
polymerizable formulations as photo hardeners. 
The borate compounds according to the invention can be used not only as 
initiators for photopolymerization reactions but also as thermal 
polymerization initiators. 
Subsequently, the invention also provides for the use of the compounds of 
formula I or I', or Ia or Ia', as initiators for the thermal 
polymerization of compounds containing ethylenically unsaturated double 
bonds, and a process for the thermal polymerization of compounds 
containing ethylenically unsaturated double bonds, which comprises 
employing at least one compound of the formula I or 1', or 1a or 1a' as 
polymerization initiator. 
The examples which follow illustrate the invention in more detail. Parts 
and percentages are, as in the remainder of the description and in the 
claims, by weight, unless stated otherwise. 
Where alkyl radicals having more than three carbon atoms are referred to 
without any mention of specific isomers, the n-isomers are meant in each 
case.