Cationic photopolymerisation process.

description

0001The invention relates to a process for the cationic photopolymerization of epoxides, cyclic ethers and alkyl vinyl ethers in the presence of a photoinitiator system.

0002One method of generating carbocations that are able to initiate the cationic polymerization of epoxides, cyclic ethers or alkyl vinyl ethers is based on the transfer of electrons from free radicals to onium salts. Such methods are described, for example, by FAM Abdul Rasoul, A. Ledwith and Y. Yagci in Polymer 19, 1219 (1975), by Y. Yagci and A. Ledwith in J. Polym. Sci., Polym. Chem. Ed. 26, 1911 (1988), by Y. Yagci and W. Schnabel in Makromol. Chem. Macromol. Symp. 13/14, 161 (1988) and by H.-J. Timpe in Pure Appl. Chem.<u style="single">60</u>, 1033 (1988). Electron-rich free radicals that can be used for this process can be generated by photolysis or thermolysis of suitable compounds. Onium salts which have proven to be particularly suitable for initiating the cationic polymerization are, for example, diazonium salts such as p-chlorophenyldiazonium hexafluorophosphate, iodonium salts such as diphenyliodonium hexafluorophosphate and triarylsulfonium salts such as triphenylsulfonium hexafluoroarsenate.

0003In addition to the onium salt, the photoinitiator systems mentioned above contain either photochemical α-splitters, such as, for example, benzil dimethyl ketal (H. Baumann and H.-J. Timpe, J. Prakt. Chem. <u style="single">326</u>, 529 (1984)), which form colored photolysis products or contain long-wave absorbing sensitizers, such as, for example, thioxanthones. The disadvantage is that only thin layers can be hardened cationically. When using triarylsulfonium salts, malodorous mercaptans are formed during the irradiation, which preclude the use of the radiation-curable mixture in the food sector.

0004The object of the present invention is to demonstrate a process for the cationic polymerization of epoxides, cyclic ethers and alkyl vinyl ethers, in which advantages over the already known photoinitiator systems can be achieved by means of new photoinitiator systems.

0005Surprisingly, this object is achieved by using a combination of a free-radical initiator and certain heteroaromatic salt-like compounds.

0006The present invention relates to a process for the cationic photopolymerization of epoxides, cyclic ethers or alkyl vinyl ethers in the presence of a photoinitiator system, which is characterized in that a mixture of as photoinitiator system<ul id="ul0001" list-style="none"><li>a) at least one radical-providing photoinitiator and</li><li>b) at least one heteroaromatic salt-like compound with at least one grouping of the general formula</li></ul><chemistry id="chem0001" num="0001"><img file="EP0441232A2_D0001.tif" /></chemistry> is used, wherein R is an optionally substituted, alkyl, alkenyl, alkynyl, hetaryl, alkenylcarbonyl, alkynecarbonyl, alkoxycarbonyl, carbamoyl, alkylsulfonyl, arylsulfonylaminosulfinyl radical, a substituted cycloalkyl radical or an optionally substituted radical Represents hetaryl cation, with the proviso that the maximum of the long-wave absorption band of this heteroaromatic salt-like compound is below 350 nm.

0007Preferred radical-providing photoinitiators (a) are acylphosphine oxide compounds, bisacylphosphine oxide compounds and 6-acyl-6H-dibenz [c, e] [1,2] oxaphosphorine-6-oxides.

0008Suitable free-radical photoinitiators are, for example, also benzoin ethers and lower alkyl ketals of the general formula<chemistry id="chem0002" num="0002"><img file="EP0441232A2_D0002.tif" /></chemistry> wherein alkyl is an alkyl radical having 1 to 4 carbon atoms and Ar¹ and Ar² are identical or different from one another and represent phenyl or phenyl substituted by alkyl having 1 to 4 carbon atoms or halogen.

0009Preferred heteroaromatic salt-like compounds (b) are salts of six-membered heteroaromatics containing 1 to 3 N atoms in the ring system containing a group of the general formula (I), the core-substituted derivatives thereof or the benzanellated or hetarylanellated derivatives thereof, in particular compounds of the general formula ( II)<chemistry id="chem0003" num="0003"><img file="EP0441232A2_D0003.tif" /></chemistry> wherein R has the same meaning as in the grouping of the general formula (I), R 'for hydrogen or one or more optionally substituted alkyl groups, optionally substituted phenyl groups, alkoxy groups, vinyl groups, formyl groups, nitro -Groups or halogen atoms, where two compounds of the formula (II) can also be connected to one another via the radicals R or R ', and A^⊖ stands for the anion of an inorganic or organic acid with the proviso that no anion A^⊖ is present if one of the radicals R or R 'represents a radical carrying an anionic grouping. Preference is also given to those compounds of the general formula (II) in which R represents an alkyl group having 1 to 6 carbon atoms or an optionally substituted alkoxycarbonyl group having 1 to 6 carbon atoms in the alkoxy group or an N, N which is optionally substituted identically or asymmetrically Dialkylcarbamoyl radical, where the substituents on the nitrogen atom of the carbamoyl group can also be connected to one another to form a ring. R 'in the compounds of the general formula (II) preferably represents a hydrogen atom or one or more, optionally substituted, alkyl groups, in particular a hydrogen atom or one or two methyl groups. Examples of preferred heteroaromatic, salt-like compounds (b) are N- (carbamoyloxy) pyridinium salts, N- (carbamoyloxy) picolinium salts, N-alkoxypyridinium salts, N-aryloxylutidinium salts, N-alkoxypicolinium salts, N-alkoxylutidinium salts, Alkoxycarbonyloxy) pyridinium salts, N- (alkoxycarbonyloxy) picolinium salts and N- (alkoxycarbonyloxy) lutidinium salts, the salts contained as heteroaromatic compound (b) in each case being a methanesulfonate, benzenesulfonate, toluenesulfonate, May contain alkyl sulfonate, tetrafluoroborate, hexafluoroarsenate, hexafluoroantimonate, hexafluorophosphate or trifluoromethanesulfonate anion.

0010The advantages of the photoinitiator systems to be used for the process according to the invention include the fact that after irradiation they can be used practically odorless and in thicker layers.

0011The following is to be explained in detail about the method according to the invention.

0012Suitable monomers to be polymerized according to the invention are epoxides, alkyl vinyl ethers and cyclic ethers.

0013Examples of epoxides can be: mono-1,2-epoxide such as epichlorohydrin, propylene oxide, cyclohexene oxide or a glycidyl ether of a monohydric alcohol or phenol such as n-butylglycidyl ether or phenylglycidyl ether, a glycidyl ester such as glycidyl acrylate or glycidyl methacrylate, preferably an epoxy resin, in particular an epoxy resin such that has at least one group of the formula which is bonded directly to an oxygen atom<chemistry id="chem0004" num="0004"><img file="EP0441232A2_D0004.tif" /></chemistry> contains, wherein either R¹ and R³ each represent a hydrogen atom, in which case R² represent a hydrogen atom or a methyl group, or R¹ and R³ together represent -CH₂CH₂-, in which case R² represents a hydrogen atom.

0014Examples of such resins are polyglycidyl and poly (β-methylglycidyl) esters which can be obtained by reacting a compound containing two or more carboxylic acid groups per molecule with epichlorohydrin, glycerol dichlorohydrin or β-methylepichlorohydrin in the presence of alkali. Such polyglycidyl esters can differ from aliphatic polycarboxylic acids, for example Succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid or dimerized or trimerized linoleic acid, of cycloaliphatic polycarboxylic acids such as tetrahydrophthalic acid, 4-methyltetrahydrophthalic acid, hexahydrophthalic acid and 4-methylhexahydrophthalic acid and isophenephthalic acid and phthalic acid and isophene phthalic acid and phthalic acid and phthalic acid and phthalic acid and isophene phthalic acid and isophene phthalic acid and phthalic acid and isophene phthalic acid and phthalic acid and isophene phthalic acid and isophene phthalic acid and phthalic acid and isophene phthalic acid and phthalic acid and phthalic acid and phthalic acid from phthalic acid and phthalic acid and phthalic acid and phthalic acid from phthalic acid and phthalic acid, such as Further suitable polyglycidyl esters can be obtained by polymerizing the glycidyl esters of olefinically unsaturated carboxylic acids, in particular glycidyl acrylate and glycidyl methacrylate.

0015Further examples are polyglycidyl and poly (β-methylglycidyl) ethers which are produced by reacting a compound containing at least two free alcoholic and / or phenolic hydroxyl groups per molecule with the corresponding epichlorohydrin under alkaline conditions, or in the presence of an acidic catalyst with the following Alkali treatment are available. These ethers can be mixed with poly (epichlorohydrin) from acyclic alcohols such as ethylene glycol, diethylene glycol and higher poly (oxyethylene) glycols, propane-1,2-diol and poly- (oxypropylene) glycols, propane-1,3-diol , Poly (oxytetramethylene) glycols, pentane-1,5-diol, hexane-2,4,6-triol, glycerin, 1,1,1-trimethylolpropane, pentaerythritol and sorbitol, from cycloaliphatic alcohols such as resorcite, quinite, bis - (4-hydroxycyclohexyl) methane, 2,2-bis (4-hydroxycyclohexyl) propane and 1,1-bis (hydroxymethyl) cyclohexene-3, and from alcohols with aromatic nuclei, such as N, N-bis (2-hydroxyethyl) aniline and p, p '-Bis- (2-hydroxyethylamino) diphenylmethane. They can also be obtained from mononuclear phenols such as bis (4-hydroxyphenyl) methane (otherwise known as bisphenol F), 4,4'-dihydroxyphenyl, bis (4-hydroxyphenyl) sulfone, 1,1,2,2- Tetrakis (4-hydroxyphenyl) ethane, 2,2-bis (4-hydroxyphenyl) propane (otherwise known as bisphenol A) and 2,2-bis (3,5-dibromo-4-hydroxyphenyl) propane , and from aldehydes such as formaldehyde, acetaldehyde, Produce chloral and furfural with phenol itself and phenol ring-substituted by chlorine atoms or alkyl groups each having up to nine carbon atoms, such as 4-chlorophenol, 2-methylphenol and 4-tert-butylphenol.

0016Poly (N-glycidyl) compounds can also be used, for example N-glycidyl derivatives of amines such as aniline, n-butylamine, bis (4-aminophenyl) methane and bis (4-methylaminophenyl) methane, triglycidyl isocyanurate and N , N '-diglycidyl derivatives of cyclic alkylene ureas such as ethylene urea and 1,3-propylene urea and hydantoins such as 5,5'-dimethylhydantoin. In general, however, these are not preferred.

0017It is also possible to use poly (S-glycidyl) compounds, for example di- (S-glycidyl) derivatives of dithiols such as ethane-1,2-dithiol and bis- (4-mercaptomethylphenyl) ether, but these will not either prefers.

0018Examples of epoxy resins with groups of the above formula, in which R¹ and R³ together represent a -CH₂CH₂ group, are bis (2,3-epoxycyclopentyl) ether, 2,3-epoxycyclopentyl glycidyl ether and 1,2-bis-2, 3-epoxycyclopentyloxy) ethane.

0019Also suitable are epoxy resins in which the 1,2-epoxy groups are bonded to heteroatoms of various types, for example the glycidyl ether / glycidyl ester of salicylic acid.

0020Also usable are epoxy resins in which some or all of the epoxy groups are middle-class, such as vinylcyclohexene dioxide, limonene dioxide, dicyclopentadiene dioxide, 4-oxatetracyclo- [6.2.1.0^2,7.0^3,5] undecyl-9-glycidyl ether, 1,2-bis (4-oxatetracyclo [6.2.1.0^2,7.0^3,5] undecyl-9-oxy) -ethane, the 3,4-epoxycyclohexylmethyl ester of 3 ', 4'-epoxicyclohexanecarboxylic acid and its 6,6'-dimethyl derivative, the bis (3,4-epoxicyclohexanecarboxylic acid ester) of ethylene glycol, 3- (3rd , 4-epoxicyclohexyl) -8,9-epoxy-2,4-dioxaspiro [5.5] -undecane and epoxidized butadienes or copolymers of butadiene with ethylene compounds such as styrene and vinyl acetate.

0021If desired, epoxy resin mixtures can be used.

0022Particularly preferred, optionally pre-extended epoxy resins used in the process according to the invention are the diglycidyl ethers of dihydric phenols, such as 2,2-bis (4-hydroxyphenyl) propane and bis (4-hydroxyphenyl) methane, and of dihydric aliphatic alcohols, such as butane-1,4-diol.

0023If desired, the epoxy resin can be subjected to mixed curing with a polyhydric alcohol, ie a compound having at least two alcoholic, preferably primary, hydroxyl groups in the molecule. The polyhydric alcohol is preferably present in an amount sufficient to provide 0.5 to 1.5, in particular 0.75 to 1.25, alcoholic hydroxyl groups per 1,2-epoxy group of the epoxy resin. In addition to the alcoholic hydroxyl groups, the polyhydric alcohol preferably contains only carbon, hydrogen and optionally oxygen and halogen atoms present as ether oxygen or acetal or carbonyl groups. Furthermore, the polyhydric alcohol preferably has a molecular weight of at least 100 and in particular higher than 1000. Suitable polyhydric alcohols are, for example, poly (oxyethylene) glycols, poly (oxypropylene) glycols, poly (oxytetramethylene) glycols, polyepichlorohydrins, poly (oxyethylene), poly (oxypropylene), or poly ( oxyetetramethylene) -triols, which are obtained by polymerizing ethylene oxide, propylene oxide or Tetrahydrofuran in the presence of glycerol or 1,1,1-trimethylolpropane are available, polycaprolactones with hydroxyl end groups, copolymers of styrene with allyl alcohol, polyvinyl alcohols, hydroxypropyl cellulose, hydroxy-containing polyvinyl acetals and partial esters of cellulose, for example a cellulose acetate butyrate.

0024Vinyl ethers which can be cationically polymerized by the process according to the invention are vinyl ethers of aliphatic monohydric alcohols having 1 to 12, preferably 1 to 4, carbon atoms and the 3,4-dihydro-2H-pyranyl- (2) methyl ester of 3,4-dihydro -2H-pyran-2-carboxylic acid, isobutyl vinyl ether, methyl vinyl ether, trimethylolpropane trivinyl ether, glycerol trivinyl ether, triethylene glycol divinyl ether, 1,4-cyclohexane dimethanol divinyl ether, the vinyl ethers of ethylene glycol and poly (oxyethylene glycols) and cyclic vinyl ethers having at least two cyclic vinyl ether groups, each of which forms part of a 3,4-dihydro-2H-pyran core, such as 3,4-dihydro-2H-pyranyl- (2 ) methyl ester of 3,4-dihydro-2H-pyran-2-carboxylic acid and its prepolymers.

0025A simple example of a suitable cyclic ether is tetrahydrofuran.

0026The monomers can advantageously be purified before the polymerization, for example cyclohexene oxide by distillation over CaH₂ under reduced pressure, tetrahydrofuran after storage over NaOH by distillation over CaH₂, or the vinyl ethers such as N-butyl vinyl ether by washing with aqueous sodium hydroxide solution (approx. 10% ig) and water, drying with CaCl₂ and Na₂SO₄ and distilling off over CaH₂.

0027The photoinitiator system to be used according to the invention consists of a mixture of<ul id="ul0002" list-style="none"><li>a) at least one radical-providing photoinitiator and</li><li>b) at least one heteroaromatic salt-like compound with at least one grouping of the general formula (I)</li></ul><chemistry id="chem0005" num="0005"><img file="EP0441232A2_D0005.tif" /></chemistry> where R has the meaning given above.

0028Acylphosphine oxides and derivatives thereof are particularly suitable as radical-forming photoinitiators (a).

0029As examples of suitable phosphine oxide compounds (cf. e.g. EP-A-00 07 508, EP-A-00 57 474, EP-A-00 73 413 and DE-A 31 39 984) may be mentioned: 2,2-dimethyl-propionyldiphenylphosphine oxide, 2,2-dimethyl-heptanoyl-diphenylphosphine oxide, 2,2-dimethyl-octanoyl-diphenylphosphine oxide, 2,2-dimethyl-nonanoyl-diphenylphosphine oxide, 2,2-dimethyl-octanoyl-phenylphosphonic acid methyl ester, 2- Methyl-2-ethyl-hexanoyl-diphenylphosphine oxide, 1-methyl-1-cyclohexanecarbonyl-diphenylphosphine oxide, 2,6-dimethylbenzoyl-diphenylphosphine oxide, 2,6-dimethoxybenzoyl-diphenylphosphine oxide, 2,6-dichlorobenzoyl-diphenylphoisophine oxide, 2,6-Dimethoxybenzoyl-phenylphosphonic acid methyl ester, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, 2,4,6-trimethylbenzoyl-phenylphosphonic acid methyl ester, 2,3,6-trimethylbenzoyl-diphenylphosphine oxide, 2,3,5,6-tetramethylbenzoyl-diphenylphosphine oxide 2,4,6-trimethoxybenzoyl-diphenylphosphine oxide, 2,4,6-trichlorobenzoyl-diphenylphosphine oxide, 2-chloro-6-methylthiobenzoyl-diphenylphosphine oxide, 2,4,6-trimethylbenzoyl-naphthylphosphinic acid methyl ester, 1,3-dimethoxynaphthalene-2-carbonyl diphenylphosphine oxide, 2,8-dimethoxynaphthalene-1-carbonyl-diphenylphosphine oxide, 2,4,6-trimethylpyridine-3-carbonyl-diphenylphosphine oxide, 2,4-dimethylquinoline-3-carbonyl-diphenylphosphine oxide, 2,4-dimethoxyfuran-3-carbonyl-diphenylphosphine oxide and 2,4-Dimethylfuran-3-carbonyl-phenylphosphonic acid methyl ester.

0030As examples of suitable bisacylphosphine oxides (cf. e.g. DE-A-36 33 436) may be mentioned: Bis (2,6-dichlorobenzoyl) phenylphosphine oxide, Bis (2,6-dichlorobenzoyl) -2,5-dimethylphenylphosphine oxide, Bis (2,6-dichlorobenzoyl) -4-ethoxyphenylphosphine oxide, Bis (2,6-dichlorobenzoyl) -4-chlorophenylphosphine oxide, Bis (2,6-dichlorobenzoyl) -4-propylphenylphosphine oxide, Bis (2,6-dichlorobenzoyl) -4-biphenylyl-phosphine oxide, Bis (2,6-dimethoxybenzoyl) -2,5-dimethylphenylphosphine oxide, Bis (2,6-dimethoxybenzoyl) phenylphosphine oxide, Bis (2,6-dichloro-3,4,5-trimethoxybenzoyl) -2,5-dimethylphenylphosphine oxide, Bis (2-methyl-1-naphthoyl) phenylphosphine oxide, Bis (2-methyl-1-naphthoyl) -4-bisphenylyl phosphine oxide, Bis (2-methoxy-1-naphthoyl) -2,5-dimethylphenylphosphine oxide, Bis (2-methoxy-1-naphthoyl) -4-ethoxyphenylphosphine oxide.

0031Suitable 6-acyl- (6H) -dibenz [c, e] [1,2] oxaphosphorin-6-oxides are listed, for example, in DE-A-38 27 735 and in EP-A-0 304 782.

0032However, benzoin ethers of the formula can also be used, for example, as free-radical-providing photoinitiators (a)<chemistry id="chem0006" num="0006"><img file="EP0441232A2_D0006.tif" /></chemistry> such as benzoin methyl ether, benzoin ethyl ether, benzoin n-propyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin isobutyl ether, benzoin amyl ether or benzoin hexyl ether, and lower alkyl ketals of the general formula<chemistry id="chem0007" num="0007"><img file="EP0441232A2_D0007.tif" /></chemistry> in which alkyl is an alkyl radical having 1 to 4 carbon atoms, such as, for example, methyl, ethyl, propyl, isopropyl, n-butyl and i-butyl - where the alkyl radicals can be identical or different from one another, and Ar 1 and Ar 2 are the same or different from one another and are phenyl or phenyl substituted by alkyl having 1 to 4 carbon atoms or halogen, such as chlorine or bromine, such as tolyl, chlorophenyl or bromophenyl. An example of lower alkyl ketals is benzil dimethyl ketal. Attention is also drawn to EP-A-0 242 330, in which similar radical-providing compounds are listed.<ul id="ul0003" list-style="none"><li>b) As heteroaromatic salt-like compounds with at least one grouping of the general formula (I)<chemistry id="chem0008" num="0008"><img file="EP0441232A2_D0008.tif" /></chemistry> where R has the meaning given above, in particular six-membered heteroaromatic rings with one, two or even three ring nitrogen atoms, their nucleus-substituted derivatives, including the benzanellated and hetarylanellated representatives, are suitable. The term salt-like compound also includes inner salts, ie ionic compounds in which the cationic and anionic groups are linked to one another by covalent bonds. Suitable heteroaromatic salt-like compounds (b) are in particular the pyridinium, pyrazinium and pyrimidinium salts which contain a group of the formula (I) above incorporated in the heteroaromatic ring, furthermore the nucleus-substituted derivatives of these salts which have one or more nucleus substituents of the above specified type contained in the heteroaromatic ring, and also fused derivatives of these salts, such as benzanellated pyridinium salts of the type in question, such as the corresponding, optionally nucleus-substituted, quinolinium, isoquinolinium and phenanthridinium salts. In the general formula (I), R can represent an optionally substituted alkyl radical and a cycloalkyl radical. Alkyl radicals, in particular alkyl groups having 1 to 6 carbon atoms, are preferred for the radical R in the grouping of the formula (I).</li></ul>

0033The preferred core substituents for these salts include, in particular, the optionally substituted alkyl radicals. Preferred anions for these salts include benzenesulfonate, tosylate, alkylsulfonate, trifluoromethanesulfonate or tetrafluoroborate anions. The N-alkoxy and N-aryloxypyridinium salts, the N-alkoxy and N-aryloxypicolinium salts and also the N-alkoxy and N-aryloxyputinium salts have proven to be particularly advantageous for the use according to the invention.

0034Examples of compounds (b) with groupings of the formula (I) are<chemistry id="chem0009" num="0009"><img file="EP0441232A2_D0009.tif" /></chemistry>

0035In these formulas (III) to (XI), the radical R preferably denotes an alkyl radical having 1 to 6 carbon atoms, such as the methyl, ethyl or i-propyl group. The radical R 'in these formulas is hydrogen (corresponding to an unsubstituted heteroaromatic ring) or one or more core substituents of the type indicated above. R' is preferably hydrogen or one or more, optionally substituted, alkyl groups, aryl groups, alkoxy groups or chlorine. In particular, R 'represents a hydrogen atom or one or more methyl groups, preferably 2-methyl, 2,6-dimethyl, or in the formulas (III), (IV) and (IX) also 3,5-dimethyl. In formula (IX ) R "represents an alkylidene radical, in particular having 2 to 6 carbon atoms or a xylidene radical, for example the p-xylidene radical. Furthermore, in the formulas (III) to (XI) A^⊖ for an acid anion, with the benzenesulfonate, p-toluenesulfonate, tetrafluoroborate, trifluoromethanesulfonate, hexafluorophosphate, hexafluoroantimonate and hexafluoroarsenate being preferred.

0036Compounds of the formula (III) are of particular importance, the compounds in which the radical R 'has a hydrogen atom or one or two methyl groups and the radical R an alkyl group having 1 to 3 carbon atoms, such as methyl, have proven particularly advantageous Represents ethyl or i-propyl.

0037Examples of compounds (b) are: N-methoxy-2-picolinium hexafluoroarsenate, N-methoxy-2-picolinium methyl sulfate, N-methoxy-2-picolinium methanesulfonate, N-methoxy-2-picolinium trifluoromethanesulfonate, N-methoxy-2-picolinium-n-octyl sulfonate, N-methoxy-2-picolinium o / p-dodecylbenzenesulfonate, N-methoxy-2-picolinium hexafluoroantimonate, N-methoxy-2-picolinium methanesulfonate, N-ethoxy-2-picolinium tetrafluoroborate, N-ethoxy-2-picolinium p-toluenesulfonate, N-ethoxy-2-picolinium tetrafluoroborate, N-ethoxy-2-picolinium hexafluorophosphate, N-ethoxy-2-picolinium hexachloroantimonate, N-isopropoxy-2-picolinium p-toluenesulfonate, O- (2'-picolinium-1'-yl) -3-hydroxy-hexafluoroarsenate, N-methoxy-4-picolinium methanesulfonate, N-methoxy-4-picolinium trifluoromethanesulfonate, N-methoxy-4-picolinium p-toluenesulfonate, N-ethoxy-4-methoxypyridinium tetrafluoroborate, 1,4-dimethoxy-pyridinium tetrafluoroborate, N-tert-butoxy-pyridinium perchlorate, N-methoxy-3,5-lutidinium p-toluenesulfonate, N-methoxy-2,6-lutidinium methanesulfonate, N-methoxy-2,6-lutidinium trifluoromethanesulfonate, N-methoxy-2,6-lutidinium trifluoromethanesulfonate, N-methoxy-2,6-lutidinium p-toluenesulfonate, N-methoxy-2, 6-lutidinium hexachloroantimonate, N-ethoxy-2,5-lutidinium tetrafluoroborate, N-ethoxy-2,6-lutidinium hexachloroantimonate, N-ethoxy-2,6-lutidinium hexafluorophosphate, O- (2 ', 6'-lutidinium-1'-yl) -3-hydroxypropane sulfonate, N-methoxy-2-styrylpyridinium p-toluenesulfonate and N, N'-p-xylylenoxy-bis- (2-methylpyridinium) bis (hexafluoroarsenate).

0038The heteroaromatic compounds (b) of the type described above can be prepared by customary and customary processes known from the literature or in analogy to these. In this context, reference is made, for example, to RA Abramovitch and EM Smith in "Pyridine and its Derivatives", Vol. 14 Supplement, Part 2, page 1 ff, J. Wiley, New York (1974).

00391-ethoxy-2-methylpyridinium hexafluorophosphate (EMP^⊕PF₆^⊖) can, for example, also according to the one by C. Reichardt in Chem. Ber. 99, 1769 (1966).

0040For the process according to the invention for cationic photopolymerization, the free-radical photoinitiators (a) are generally used in amounts of 0.05 to 10, preferably 2 to 8 percent by weight, the heteroaromatic salt-like compounds (b) are generally used in amounts of 1 to 15, preferably 2 to 10 percent by weight, the percentages by weight based in each case on the reactive monomer (ie epoxy, cyclic ether or alkyl vinyl ether).

0041The photopolymerization process preferably uses actinic radiation with a wavelength of 200 to 600 nm. Suitable actinic radiation sources include carbon arcs, mercury vapor arcs, fluorescent tubes with ultraviolet light emitting phosphors, argon and xenon glow lamps, tungsten lamps and photographic flood lamps. Among them, mercury vapor arcs, especially sunlamps, fluorescent sunlamps and metal halide lamps, are the most suitable. The time required for exposure depends on various factors, including, for example, the polymerizable substrate used in each case, the type of light source and its distance from the irradiated material. Those skilled in photopolymerization techniques can easily determine the appropriate times. If it is necessary that the product so photopolymerized is still curable when heated with a blended hot hardener, then the irradiation must of course be carried out at a temperature below that which would occur when the photopolymerized product was largely thermoset by the hot hardener.

0042The mixtures according to the invention can be used as surface coatings. They can be applied, preferably as a liquid, to a substrate such as steel, aluminum, copper, paper or wood and irradiated. If part of the coating is polymerized, as in the case of irradiation through a mask, the unexposed areas can be washed with a solvent to remove unpolymerized portions, while the photopolymerized, insoluble portions remain in place. The compositions according to the invention can thus be used in the production of printing plates and printed circuits.

0043The mixtures can also be used as adhesives. A layer of the composition can be placed between two surfaces of articles, at least one of which is transparent to actinic radiation, such as glass, and the assembly is then irradiated and, if desired, heated to complete the polymerization.

0044The blends are also useful in the manufacture of fiber reinforced composites, including sheet molding compounds.

0045Unless stated otherwise, the parts and percentages mentioned in the examples are parts by weight or percentages by weight.

example 1

0046A curable composition was prepared by making a mixture of 0.05 part of 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 0.09 part of 1-ethoxy-2-methylpyridinium hexafluoroarsenate dissolved in dichloromethane and 5 parts of 4-vinylcyclohexene dioxide.

0047An approximately 0.05 mm (corresponding to 2 thousandths of an inch) thick film was drawn onto a glass plate and exposed to UV radiation from a high-pressure mercury lamp from a distance of approximately 25 cm. The resin cured to a hard film within 30 seconds. The film was insoluble in dipolar aprotic solvents and could not be scratched with a fingernail.

0048Part of the above curable composition, having a viscosity of about 6 centipoise at 25 ° C, was left in a transparent container for 4 months under average daylight conditions. The viscosity remained essentially the same.

0049A portion of the curable composition was applied to a steel strip. The treated steel surface was then exposed to UV radiation from a high pressure Hg lamp from a distance of about 5 cm for 15 seconds. A clear, tack-free film was formed that showed no signs of bubbles or other defects.

Examples 2 to 8

0050The experiment described in Example 1 was repeated with other picolinium salts and the irradiation time varied so that a scratch-resistant surface was formed in all cases.<tables id="tabl0001" num="0001"><img file="EP0441232A2_D0010.tif" /></tables>

Examples 9 and 10

0051If the 4-vinylcyclohexene dioxide is replaced by 1,4-cyclohexanedimethanol divinyl ether in Example 1, exposure times of 25 or 20 seconds are required.