DE4110793C1 - Organo:polysiloxane - used as photoinitiator in cationically curable organo:polysiloxane compsn. esp. contg. epoxy¨ or vinyl¨ gps. - Google Patents

Abstract

An organopolysiloxane has formula (1) (where each R is 1-4C alkyl or Ph with at least 90% of all R being Me; some R' and R and of the remainder (a) 0-70% are 2-20C (substd.) alkyl opt. interrupted by ether-0 and/or are alkaryl and/or polyether residues and (b) 30-100% are photoinitiator active gps. -R3-Q(R4)n- -I+-Q'.Y-; R3 is divalent, aliphatic 2-6C hydrocarbyl opt. interrupted by ether-O; R4 is -OR5 or (-OCmH2m)zOR6; R5 is H or 1-6C alkyl; R6 is 1-4C alkyl; m = 2 or 3; z = 1-100; n = 1-4; Y is a complex anion of B, Sb, P or As or is CF3SO3-; a = 1-100; b = 0-10; Q is p-phenylene; Q' is Ph.). Pref all R are Me; R3 is 2-6C divalent aliphatic hydrocarbyl; a = 1-50; b = 0-4; Y is SbF6-, PF6-, AsF6-, BF4- or B(CF3SO3)4-. USE/ADVANTAGE - In amt. of 0.01-10 wt% as photoinitiator in cationically curable organopolysiloxane compsn., esp. contg. epoxy or vinyl gps.; a highly compatible initiator free from detrimental effects on the (un)cured organopolysiloxane. (12pp Dwg.No.0/0)

Description

The invention relates to organopolysiloxanes which are at least one as Have photoinitiator effective group. It affects in particular those organopolysiloxanes in which the effective as a photoinitiator Group is connected to the siloxane structure via an SiC bond.

The invention further relates to a method for producing this Compounds and their use as photoinitiators for cationic curing compounds, especially epoxy or vinyl groups containing compounds.

DE-AS 15 70 284 describes a process for the production of homo- or copolymers of cyclic ethers or of cyclic acetals described by polymerization in the presence of catalysts, where as catalysts carbonium, carboxonium, oxonium, hydroxonium, Aryldiazonium, iodonium, nitrosyl or nitrohexafluoroantimonates be used. These catalysts are reported to be compared to known catalysts in terms of the rate of polymerization are more effective when used, the percentage Yield of polymers would be increased and high molecular weights achievable would be. Typical examples of such catalysts are triphenylmethylhexafluoroantimonate and iodonium hexafluoroantimonate.

DE-PS 25 18 639 relates to curable preparations consisting of an epoxy resin and an effective amount of one or more radiation sensitive aromatic onium salts as catalysts for the  Hardening with the characteristic that the onium salt is an iodonium salt of formula

[(R) _u (R¹) _b I] _c ⁺ [MQ _d ] ^{- (de)}

is where R is a monovalent aromatic radical, R¹ is a divalent aromatic radical, M is a metal or non-metal, Q is a halogen radical such as F, Cl, Br or I, a is 0 or 2, b is 0 or 1 and the sum of a + b is 2 or the valence of 1, c = de, where e corresponds to the valence of m and is therefore an integer from 2 up to and including 7 and de and thus an integer with a value is up to 8. Metals or non-metals that stand for M are the transition metals, such as Sb, Fe, Sn, Bi, Al, Ga, In, Ti, Zr, Sc, V, Cr, Mn, Cs, rare earth metals, such as the lanthanides, actinides , as well as non-metals, such as B, P, As. The complex anions of the formula MQ _d ^{- (de)} are e.g. B. BF₄ ^- , PF₆ ^- , AsF₆ ^- , SbF₆ ^- , FeCl₄ ^- , SnCl₄ ^- and BiCl₅ ^- .

These catalysts described in DE-PS 25 18 639 are used for Hardening of compounds containing epoxy groups including Organopolysiloxanes containing epoxy groups. The hardening takes place by activation of the iodonium salt by means of radiation in order to To release the Lewis acid catalyst. The radiation is preferably done with electron beams or with UV light.

In all cases, however, an effective polymer reaction only runs when salts with anions of low nucleophilicity are used, since these compounds are the strongest acids in photolysis release. In the literature (e.g. Timpe, H.J. and Baumann, H., photopolymers, Principles and Applications, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig 1988) follows the following order falling activity:

SbF₆ ^- <AsF₆ ^- <PF₆ ^- »CF₃SO₃ ^- = ClO₄ ^- = FSO₃ ^- = F₂PO₂ ^- <Cl ^- <Br ^- = 0

Such compounds containing epoxy group-containing hardeners can also be cured thermally, if one of the to be cured Preparation additionally thermally effective initiators, such as. B. copper salts, inflicts.

The iodonium salts known from the literature, such as diphenyl iodonium hexafluoroantimonate, but have the disadvantage that they in Epoxy resins, especially in organopolysiloxanes containing epoxy groups, are poorly soluble. Some improvement in tolerance was replaced by the substitution of the phenyl radicals with long-chain Alkylene residues causes. For example, bis (dodecyl-phenyl) Iodonium hexafluoroantimonate recommended as hardener. The tolerance this is iodonium salts in epoxy-functional organopolysiloxanes not satisfactory despite this substitution.

The present invention addresses the technical problem that Compatibility of photoinitiators based on iodonium salts in particular with organopolysiloxanes, which are cationically curable groups contain, improve, without affecting the polymerization reaction or the application properties of the modified Organopolysiloxanes impaired before or after their curing will.

The solution to this technical problem was the direct one Incorporation of suitable groups that trigger catalysis into the molecule of the Organopolysiloxane.

One object of the invention is therefore to develop new ones Organopolysiloxanes which have at least one effective as a photoinitiator Have group and is characterized in that the organopolysiloxanes at least one group of the general active as a photoinitiator formula

have in which

R³ is a divalent aliphatic hydrocarbon radical with 2 to 6 carbon atoms, the carbon chain of which may be interrupted by an ether oxygen,
R⁴ is -OR⁵ or [-OC _m H₂ _m ] _z OR⁶, wherein
R⁵ is a hydrogen radical or an alkyl radical having 1 to 6 carbon atoms and
R⁶ is an alkyl radical with 1 to 4 carbon atoms,
m = 2 or 3 and has a value of 2 to 3 in the average molecule,
z = 1 to 100,
n = 1 to 4,
Y ^- a complex anion of boron, antimony, phosphorus or arsenic or the anion CF₃SO₃ ^- is.

Examples of photoinitiator groups bonded to Si are:

To explain the residues and indices in more detail, the following is carried out:

R³ is a divalent aliphatic hydrocarbon residue with 2 up to 6 carbon atoms, e.g. B. the rest- (CH₂) ₂-, - (CH₂) ₄-, - (CH₂) ₆-, or a branched residue, e.g. B.

The hydrocarbon chain of the radical R³ can be interrupted by an ether oxygen and z. B. the formula -CH₂-CH₂-O-CH₂-CH₂- correspond.
R⁴ has either the meaning of the radical -OR⁵ or the radical [-OC _m H₂ _m ] _z OR⁶. R⁵ is either a hydrogen radical or an alkyl radical with 1 to 6 carbon atoms, which can optionally be branched.

In the polyether group [-OC _m H₂ _m ] _z OR⁶, R⁶ is an alkyl radical having 1 to 4 carbon atoms, which originates from the starting alcohol in the preparation of the polyether monool. m has a value of 2 or 3, so that the oxyalkylene group can be an oxyethylene or oxypropylene group. In the average molecule, m should have a value of 2 to 3. The oxyethylene and oxypropylene groups can be present in blocks or in a statistical distribution. The number of oxyalkylene units in the single molecule is 1 to 100.

Y ^- is a complex anion of boron, antimony, phosphorus or arsenic or the anion CF₃SO₃ ^- . Y ^- is preferably a complex anion of the formula Sb₆ ^- , PF₆ ^- , AsF₆ ^- , BF₄ ^- or B (CF₃SO₃) ₄ ^- .

The index n can have a value from 1 to 4. Preferably n a value of 1 or 2, in particular a value of 1.

As organopolysiloxanes with at least one effective as a photoinitiator In particular, those siloxanes are preferred in which the photoinitiator group via an SiC bond with the siloxane skeleton is connected and their compatibility with the different to be hardened Organopolysiloxanes by choosing the appropriate structure and substitution can be optimized.

A preferred subject of the present invention are therefore organopolysiloxanes, which of the general formula  

correspond with
the radicals R1 are identical or different and each represent lower alkyl radicals having 1 to 4 carbon atoms or phenyl radicals, but at least 90% of the radicals R1 are methyl radicals,
the radicals R² can have part of the meaning of the radicals R¹ and the other radicals R² too
0 to 70% of alkyl radicals having 2 to 20 carbon atoms, the carbon chain of which may be interrupted by an ether oxygen and which may be substituted, and / or are alkaryl radicals and / or polyether radicals, and to
30 to 100% residues of the general formula

are in which R³, R⁴, Y ^- and n have the meaning already given,
the index a = 1 to 100 and
the index b = 0 to 10,
with the proviso that in the average molecule at least 1 R² is an iodonium salt group.

To explain the residues and indices in more detail, the following is carried out:

The radicals R 1 are alkyl radicals with 1 to 4 carbon atoms, such as methyl, Ethyl, propyl or butyl radicals, the propyl and butyl radicals can also be branched. R1 can also mean a Phenylrestes have. At least 90% of the residues R¹ must have methyl residues be. All R 1 radicals are preferably methyl radicals.

The radicals R² can partly represent the meaning of the radicals R¹ to have. However, there must be at least 1 residue in the average molecule R² is an iodonium salt group of the formula mentioned in claim 1. It can all residues R² with the exception of a residue that one Must be iodonium salt group, the meaning of the radicals R¹. However can the residues R² in addition to the meaning of an iodonium salt group and the meaning of the radical R¹ also assume the following meaning:

• a) alkyl radicals having 2 to 20 carbon atoms, such as ethyl, butyl, i-butyl, hexyl, octyl, dodecyl, hexadecyl radicals, the carbon chain the alkyl radicals are interrupted by an ether oxygen can be, such as in the CH₃CH₂-O-CH₂CH₂- or CH₃ (CH₂) ₄-O- (CH₂) ₄-. The residues can also be substituted. example one such substituent is the hydroxyl group.
• b) alkaryl radicals, such as in particular the 2-phenylpropyl and the 2-ethylhexyl radical.
• c) polyether residues which are connected to an Si atom, preferably via an SiC bond. Examples of such polyether radicals are the radicals- (CH₂) ₃-O- (C _m H₂ _m ) _z OR⁶, where m, z and R⁶ have the definition already given.

The number ratio of the iodonium salt groups to the sum of the aforementioned Residues R² with the meaning a), b) and c) is 30 to 100 to 70 to 0.

The index a in the polysiloxane molecule indicates the number of difunctional ones Si units and has a value of 1 to 100, preferably from 1 to 50. The index b indicates the number accordingly of the trifunctional Si units and has a value from 0 to 10, preferably from 0 to 4. An unbranched polysiloxane molecule according to the invention thus shows an average of at least 4 and at most 202 Si atoms.

The lower limit for the iodonium salt group content is after Definition of claim 1 at least 1 group per average Molecule. However, preferably in the average molecule Silicon atom 0.2 to 0.4 radicals R² the meaning of an iodonium salt group to have.

Another object of the invention is an advantageous Process for the preparation of the compounds according to the invention. Mark this procedure is that one

• a) Organopolysiloxanes of the general formula in which
  the radicals R¹ have the meaning already given and
  some of the radicals R⁷ can have the meaning of the radicals R¹ and the other radicals R⁷ too
  0 to 70% of alkyl radicals having 2 to 20 carbon atoms, the carbon chain of which may be interrupted by an ether oxygen and which may be substituted, and / or are alkaryl radicals and / or polyether radicals, and to
  30 to 100% residues of the general formula are in which the radicals R³ and R⁴ and the index n have the meaning already given,
  with the proviso that in the average molecule at least 1 R⁷ the meaning of the rest Has,
  with, based on aryl groups, at least equimolar amounts of phenyl iodosotosylate or phenyl iodosodiacetate in the presence of a solvent at temperatures from 0 to 60 ° C. and then
• b) the intermediate obtained with, based on iodonium groups, at least equimolar amounts of a salt of the formula A⁺ · Y ^- (A⁺ = alkali ion, Y ^- as already stated) and the precipitated alkali metal tosylate or alkali metal diacetate and any excess present Salt A⁺ · Y ^- filtered off.

This process according to the invention can be carried out by the following reaction scheme are explained in more detail:

In stage a) the preferred solvent is alkyl chlorides, such as B. dichloromethane, mixed with glacial acetic acid. For implementation of the organopolysiloxane with phenyliodonium tosylate is set at least  equimolar amounts, but preferably about 10 to 20% excess, of phenyl iodosotosylate.

The reaction takes place at temperatures of about 0 to 60 ° C., preferably 0 to 40 ° C. The acetic acid is neutralized with a suitable one Base such as B. sodium bicarbonate, in aqueous solution and separates the aqueous phase.

In stage b) the ion Y is introduced ^- by reacting the intermediate product obtained with at least equimolar amounts of a salt of the formula A⁺ · Y ^- in an inert solvent. A is an alkali metal, preferably sodium. The precipitated alkali metal tosylate is then filtered off.

The organopolysiloxane modified according to the invention can now be obtained directly in the form of the solution obtained or, after removal of the solvent, can be used in pure form.

Another object of the invention is the use of Compounds according to the invention as photoinitiators for cationic curable organopolysiloxanes containing in particular epoxy or vinyl groups in amounts of 0.01 to 10% by weight, based on the total weight from organopolysiloxane to be hardened and photoinitiator siloxane.

The use of the organopolysiloxanes according to the invention is particularly preferred as photoinitiators in amounts of 0.5 to 5 wt .-%, based on total weight as described above.

According to the prior art, it is possible to use the inventive To use catalysts together with sensitizers, which cause the catalysts already by exposure to light longer wavelength can be activated.

It is also possible to use the catalysts according to the invention for the thermal Hardening of organopolysiloxanes containing epoxy or vinyl groups to use when looking at the mixture of compound to be hardened and catalyst is added as a further component of copper salts.

In the following examples, the preparation of the invention Compounds and their application properties still explained in more detail.

Example 1

51.5 g (0.674 eq) of a pendant polyhydridomethylsiloxane together with 5 g (0.037 mol) of allylphenyl ether in a 250 ml Four-necked flask with stirrer, dropping funnel, thermometer and reflux condenser submitted and heated to 50 ° C with stirring. After encore of hexachloroplatinic acid (20 ppm platinum) is further heated until to 100 ° C, and slowly add another 39.5 g (0.295 mol) of allylphenyl ether added in such a way that through the immediate onset of exothermic Reaction a temperature of 140 ° C is not exceeded. After the end of the dropwise addition (duration 0.5 h) becomes 30.0 g under the same conditions (0.4 mol) of 1-octene was added dropwise and the reaction mixture was added for as long Maintained at 120 ° C until no residual SiH content can be detected. This is the case after a total reaction time of 6 h. From the reaction mixture the Pt catalyst is separated off by filtration. The excess of 1-octene and volatile by-products removed from the product. A 1 H NMR study of the hydrosilylation product shows that the resulting siloxane the approximate composition

having.

20 g (0.1 val) of the functionalized siloxane are under Stir in a mixture of 60 g acetonitrile and 6.0 g (0.1 mol) glacial acetic acid solved. When 20 g (0.05 mol) phenyl iodosotosylate is added in portions  a slight increase in temperature can be observed. After that the reaction mixture is heated to 40 ° C. in a water bath and others Stirred at this temperature for 3 h. The initially available one goes white suspension with color change from yellow-orange to brown-red Solution about. After stripping off acetonitrile and acetic acid in the The residue is taken up in vacuum in dichloromethane and any remaining Traces of acetic acid by shaking with saturated sodium hydrogen carbonate solution neutralized. The organic phase will Dried over sodium sulfate and freed from dichloromethane in vacuo.

1 H-NMR analysis of the obtained in 93% yield dark brown liquid product indicates an iodonium coupling typical signals at 8.2 ppm, and based on the coupling pattern The signals show that a substitution in the para position has taken place. Further evaluation shows that the reaction about 85% of the siloxane-bound phenyl ether groups present in Aryliodonium groups with p-toluenesulfonate as the corresponding counterion be transferred and that the aryliodonium functional siloxane by the middle formula

can be described.

10 g of the aryliodonium-functional siloxane are mixed in 150 g Ethanol / acetone mixture (2: 1) dissolved and with the on the proportion Molar equivalent amount of potassium hexafluoroarsenate (2.96 g; 0.013 mol) was stirred for several hours under the exclusion of light. After filtering the solution of the salt residue is divided.  

The solvents are removed in vacuo from one part. Here a brown, viscous oil remains, which is in ¹H-NMR as well as in 13 C NMR still the typical signals for iodonium coupling has, but no more signals in the range of p-toluenesulfonic acid has and by the middle formula

can be described. An arsenic content is determined by means of elemental analysis of 9% As (= 94.7% exchange rate, calculated 9.5% As) and an iodine content of 16.0% I found.

The utility of the polymeric aryliodonium hexafluoroarsenate functional Siloxane as photoinitiator both in solution and as Pure substance is tested by the respective proportion accordingly a concentration of 2 wt .-% siloxane-bound aryl iodonium salt is now mixed into an epoxy-functional siloxane by hydrosilylation a polydimethylsiloxane with 0.02% by weight of SiH groups was made with vinylcyclohexene oxide. This mix comes with a Wallace Knight UV lamp (medium pressure mercury arc lamp, 80 watts / cm) irradiated. An exposure time of 0.3 s is in both Cases sufficient to harden the epoxysiloxane immediately without tack.  

Example 2

With the Pt-catalyzed hydrosilylation reaction a copolymer Polydimethylsiloxane with SiH units of the composition

hydrosilylated with 2-allylethoxybenzene and converted into a product the average composition

produced.

20 g of the siloxane thus functionalized are at room temperature dissolved in 60 g of dichloromethane with stirring. Then 12 g (0.2 mol) Glacial acetic acid was added and portions of 21.2 g (0.054 mol = 20% excess) Phenyliodosotosylate added so that the temperature does not exceed 30 ° C increases. The solution immediately turns brown. It will stirred for a further 4 h at room temperature. Then 150 ml of H₂O and 10 ml of dichloromethane are added and the acidic solution is saturated Sodium bicarbonate solution adjusted to a pH of 8. The aqueous phase is then separated off in a separating funnel and the organic phase on a rotary evaporator at 35 ° C and 20 Torr for 3 h Free dichloromethane and traces of water.  

35.8 g (corresponding to a yield of 95.6%) of a dark brown, Obtained viscous product, the 1 H and 13 C NMR spectroscopy is identified as the siloxane-bound aryl iodonium salt and the middle formula

corresponds. The transfer into a suitable, highly active material for the UV curing of cationic compounds takes place after the dissolution of 10 g (0.012 eq) of this compound in 20 g of a 1: 1 mixture from ethanol and acetone by adding 3.8 g (0.015 mol = 20% excess) Sodium hexafluoroantimonate NaSbF₆ and stirring for several hours under exclusion of light. Then the suspension is filtered off Salt residue is freed and evaporated on a rotary evaporator. The dark brown highly viscous residue proves to be a product that the formula

corresponds.  

Example 3

The reaction of 4-allyl-2-methoxy-ethoxybenzene with an SiH-functional Medium composition polydimethylsiloxane

under Pt catalysis, a copolymeric siloxane results in the middle composition

30 g (0.087 eq) of the functionalized siloxane are in one Mixture of 42 g dichloromethane and 6.3 g (0.105 mol) glacial acetic acid dissolved. While stirring and cooling (ice / salt mixture) at one temperature 34.7 g (0.088 mol) of phenyl iodosotosylate are added in portions from 0 ° C. added so that the temperature does not rise above + 5 ° C. To complete addition is stirred at this temperature for a further 3 h. Already when the phenyl iodosotosylate is added, the solution changes color by forming a Meisenheimer or a charge transfer complex briefly green. As the response time increases, the color of the Solution quickly changes from red to brown. The ice bath is then removed and stirred at room temperature for 3 h.  

After neutralizing the acetic acid and stripping off the dichloromethane on Rotary evaporators are 10 g (0.014 eq) of the brown-red, highly viscous Residue, which is a siloxane of medium composition

is dissolved in 20 g of an ethanol / acetone mixture (1: 1) and with 2.7 g (0.0174 mol) of lithium trifluoromethanesulfonate in the dark stirred for several hours.

After filtering off and washing the salt residue with a little dichloromethane the solution is evaporated on a rotary evaporator and the brown-red, viscous residue, that of the formula

corresponds, again taken up in 15 g of dichloromethane. By adding a solution of the equimolar amount of boron tristriflate (6.33 g = 0.0138 mol), dissolved in 10 ml dichloromethane, is at room temperature complexed the anion of the polymeric siloxane-bound aryl iodonium salts and in the corresponding siloxane with laterally bound Iodonium (tetratrifluoromethanesulfonate) boranate units of the formula  

transferred. The elementary analysis shows a content of 0.9% B as well 10.5% I.

Claims (10)

1. Organopolysiloxanes with at least one group of the general formula which is effective as a photoinitiator in the
R³ is a divalent aliphatic hydrocarbon radical with 2 to 6 carbon atoms, the carbon chain of which may be interrupted by an ether oxygen,
R⁴ is -OR⁵ or [-OC _m H₂ _m ] _z OR⁶, wherein
R⁵ is a hydrogen radical or an alkyl radical having 1 to 6 carbon atoms and
R⁶ is an alkyl radical with 1 to 4 carbon atoms,
m = 2 or 3 and has a value of 2 to 3 in the average molecule,
z = 1 to 100,
n = 1 to 4,
Y ^- a complex anion of boron, antimony, phosphorus or arsenic or the anion CF₃SO₃ ^- is. 2. Organopolysiloxanes according to claim 1, characterized by the general formula in which
the radicals R1 are identical or different and each represent lower alkyl radicals having 1 to 4 carbon atoms or phenyl radicals, but at least 90% of the radicals R1 are methyl radicals,
some of the radicals R² can have the meaning of the radicals R¹ and the other radicals R² too
0 to 70% of alkyl radicals having 2 to 20 carbon atoms, the carbon chain of which may be interrupted by an ether oxygen and which may be substituted, and / or are alkaryl radicals and / or polyether radicals, and to
30 to 100% residues of the general formula are in which the radicals R³, R⁴, Y ^- and n have the meaning already given,
the index a = 1 to 100 and
the index b = 0 to 10,
with the proviso that in the average molecule at least 1 R² is an iodonium salt group. 3. Organopolysiloxanes according to claim 2, characterized in that all R¹ are methyl. 4. organopolysiloxanes according to claim 2 or 3, characterized in that the R³ radical is a divalent aliphatic hydrocarbon radical with 2 to 6 carbon atoms.   5. organopolysiloxanes according to one or more of the preceding claims, characterized in that a = 1 to 50. 6. organopolysiloxanes according to one or more of the preceding claims, characterized in that b = 0 to 4. 7. Organopolysiloxanes according to one or more of the preceding claims, characterized in that Y ^{- is} a complex anion of the formula SbF₆ ^- , PF₆ ^- , AsF₆ ^- , BF₄ ^- or B (CF₃SO₃) ₄ ^- . 8. organopolysiloxanes according to one or more of the preceding claims, characterized in that in the average molecule 0.2 to 0.4 radicals R² per Si atom mean an iodonium salt group to have. 9. A process for the preparation of the organopolysiloxanes according to claims 1 to 8, characterized in that

• a) Organopolysiloxanes of the general formula in which
  the radicals R¹ have the meaning already given and
  some of the radicals R⁷ can have the meaning of the radicals R¹ and the other radicals R⁷ too
  0 to 70% of alkyl radicals having 2 to 20 carbon atoms, the carbon chain of which may be interrupted by an ether oxygen and which may be substituted, and / or are alkaryl radicals and / or polyether radicals, and to
  30 to 100% residues of the general formula are in which the radicals R³ and R⁴ and the index n have the meaning already given,
  with the proviso that in the average molecule at least 1 R⁷ the meaning of the rest Has,
  with, based on aryl groups, at least equimolar amounts of phenyl iodosotosylate or phenyl iodosodiacetate in the presence of a solvent at temperatures from 0 to 60 ° C. and then
• b) the intermediate obtained with, based on iodonium groups, at least equimolar amounts of a salt of the formula A⁺ · Y ^- (A⁺ = alkali ion, Y ^- as already stated) and the precipitated alkali metal tosylate or alkali metal diacetate and any excess present Salt A⁺ · Y ^- filtered off.

10. Use of the compounds according to claims 1 to 8 as photoinitiators for cationically curable, especially epoxy or Organopolysiloxanes containing vinyl groups in amounts from 0.01 to 10% by weight, based on the total weight of organopolysiloxane to be hardened and photoinitiator siloxane.