Photoinitiators

The photoinitiator compositions of the present invention can be used in combination with various photopolymerizable organic materials, such as cyclic ethers, cyclic esters, polyvinyl acetals, epoxy resins, etc., to produce UV curable compositions and heat curable compositions. The photoinitiators of the present invention are included by the formula,

where R is a monovalent aromatic organic radical, R.sup.1 is a monovalent organic aliphatic radical, selected from alkyl, cycloalkyl and derivatives thereof, R.sup.2 is a polyvalent organic radical forming a heterocyclic or fused ring structure, selected from aliphatic radicals and aromatic radicals, X is a Group VIa element selected from sulfur and selenium, M is selected from P, As and Sb, a is a whole number equal to 0 to 3 inclusive, b is a whole number equal to 0 to 2 inclusive, c is a whole number equal to 0 or 1 and the sum of a+b+c is a value equal to 3 or the valence of X

Radicals included by R can be the same or different aromatic carbocyclic or heterocyclic radicals having from 4-20 carbon atoms which can be substituted from 1 to 4 monovalent radicals selected from C.sub.(1-8) alkoxy, C.sub.(1-8) alkyl, nitro, chloro, etc. R is more particularly phenyl, chloro phenyl, nitro phenyl, methoxy phenyl, pyridyl, etc. R.sup.1 radicals include C.sub.(1-8) alkyl, such as methyl, ethyl, etc., substituted alkyls, such as --C.sub.2 H.sub.4 OCH.sub.3, --CH.sub.2 COOC.sub.2 H.sub.5, --CH.sub.2 COCH.sub.3, etc. R.sup.2 radicals include such structures as ##STR1##

Group VIa onium salts included by formula (I) are, for example, ##STR2##

The Group VIa onium salts of formula (1) can be made by procedures shown in the copending application Ser. No. 833,279, filed Sept. 14, 1977, now abandoned of James V. Crivello and Julia H. W. Lam, and assigned to the same assignee as the present invention. An aryl iodonium salt such as diphenyliodonium hexafluoroarsenate is employed with a Group VIa compound, such as diphenylsulfide in the presence of a copper salt catalyst, for example, copper benzoate at temperatures in the range of from 50.degree. C. to 250.degree. C. for one to five hours. Other procedures which can be used are shown in J. W. Knapczyk and W. E. McEwen, J. Am. Chem. Soc., 91 (1969): A. L. Maycock and G. A. Berchtold, J. Org. Chem., 35 No. 8, 2532 (1970); H. M. Pitt, U.S. Pat. No. 2,807,648, E. Goethals and P. De Radzetzky, Bul. Soc. Chim. Belg., 73 546 (1964); H. M. Leichester and F. W. Bergstrom, J. Am. Chem. Soc., 51 3587 (1929), etc.

The Group VIa onium salts of formula (1) can be employed as photoinitiators for effecting the cure of a variety of cationically polymerizable organic materials such as epoxy resins, cyclic ethers, polyvinyl acetals, which are described previously in my copending application Ser. No. 768,074, filed Feb. 14, 1977, now U.S. Pat. No. 4,102,687 for curing phenol-formaldehyde resins and in my copending application Ser. No. 732,421, filed Oct. 14, 1976, now abandoned directed to the use of compounds of formula (1) for curing polyvinyl acetal resins.

In order that those skilled in the art will be better able to practice the present invention, the following examples are given by way of illustration and not by way of limitation. All parts are by weight.

Triphenylselenonium chloride was prepared according to the procedure of H. M. Leicester and F. W. Bergstrom, J. Am. Chem. Soc., 51 3587 (1929) starting with diphenyl selenide. The corresponding fluoroborate, hexafluoroarsenate and hexafluoroantimonate salts were prepared by adding sodium hexafluoroarsenate, sodium tetrafluoroborate or potassium hexafluoroantimonate to an aqueous solution of triphenylselenonium chloride. White crystalline solids were obtained which were dried in vacuo.

Three percent solutions of the above salts in 4-vinylcyclohexane dioxide were cured as 2 mil films at a distance of 6 inches from a GE H3T7 lamp. The following cure times were observed:

The above results show that the hexafluoro salt is a superior photosensitizer with respect to cure time as compared to the tetrafluoroborate salt.

Several sulfonium hexafluoroarsenate salts, sulfonium hexafluoroantimonate salts and selenium hexafluoroarsenate salts, were prepared by adding the corresponding anion in the form of the acid or salt, such as sodium hexafluoroarsenate to the corresponding cation structure, such as an aqueous solution of tri(3,5-dimethyl-4-hydroxy)phenyl sulfonium chloride. The procedure described by H. M. Leicester and F. W. Bergstrom, J. Am. Chem. Soc. 51 3587 (1929) was employed. The following table shows the results obtained.

It was found that 4-vinylcyclohexene dioxide compositions containing the above onium salts exhibited a faster rate of cure, as compared to comparable prior art tetrafluoroborate onium salts.

A mixture of 11.75 parts of diphenyliodonium hexafluoroarsenate, 4.065 parts of diphenyl sulfide and 0.2 part of copper benzoate was heated with stirring at a temperature of 120.degree.-125.degree. C. for 3 hours. The mixture was then poured while it was hot into a container whereupon the product crystallized. The product was extracted three times with diethylether and then air dried. There was obtained a 97% yield of triphenylsulfonium hexafluoroarsenate. The triphenylsulfonium hexafluoroarsenate product had a melting point of 195.degree.-197.degree. C. after it was further recrystallized from 95% ethanol.

A mixture of 0.02 mole solution of the triphenylsulfonium hexafluoroarsenate in styrene oxide was irradiated at 25.degree. C. in a glass vial sealed under nitrogen using a 450 watt Hanovia lamp. It was found that the styrene oxide polymerized after 5 minutes. The same procedure was repeated, except that there was used tetrahydrofuran.

The procedure of Example 3 was repeated, except that there was used 12.75 parts of diphenyliodonium hexafluoroarsenate, 2.55 parts of pentamethylene sulfide and 0.2 part of copper benzoate. A 60% yield of product, namely, phenyl penta methylenesulfonium hexafluoroarsenate was obtained after the product was recrystallized from methanol.

A mixture of 12.75 part of 4,4'-diisopropylphenyliodonium hexafluoroarsenate, 5 parts of phenoxanthene and 0.2 part of copper benzoate was heated under nitrogen with stirring at 120.degree.-125.degree. C. for 3 hours. After cooling the product was extracted with diethylether. The remaining oil was dissolved in methylene chloride and passed through a six inch column of alumina. Trituration with ether followed by cooling in an ice bath gave a white product amounting to a 41% yield of 4-isopropylphenylphenoxanthylium hexafluoroarsenate (m.p. 126.degree.-217.degree. C.) having the formula, ##STR10##

Following the procedure of Examples 3 and 5, additional Group VIa onium salts of formula (1) were prepared as shown in Table I as follows:

In addition to the Group VIa onium salts of Example 6, additional Group VIA salts were prepared following the procedure of Examples 3 and 5 as shown in Table II as follows:

In accordance with a further aspect of copending application Ser. No. 833,279, filed Sept. 14, 1977, now abandoned, a variety of triaryl Group VIa onium salts were prepared using a diaryliodonium hexafluoroarsenate, hexafluoroantimonate or hexafluorophosphate salt and a thiophenol coreactant in combination with copper benzoate and triethylamine as a cocatalyst. The diphenyliodonium hexafluoroarsenate was prepared by the procedure shown in Crivello U.S. Pat. No. 3,981,897, assigned to the same assignee as the present invention. Other procedures which can be used are, for example, M. C. Casserio et al, J. Am. Soc., 81 366 (1959). A typical procedure used in preparing such triaryl Group VIA onium salts was as follows:

A mixture of 2.75 part of thiophenol, 11.75 parts of diphenyliodonium hexafluoroarsenate, 0.2 part of copper benzoate and 4 parts of tri-n-butyl amine were heated with stirring at 120.degree.-125.degree. C. under nitrogen for 3 hours. The product after cooling was washed with diethylether and then dried. There was obtained an 86% yield of triphenylsulfonium hexafluoroarsenate. Additional triaryl Group VIa onium salts were prepared as follows following substantially the same procedure:

Although the above examples are directed to only a few of the very many compounds included within the scope of formula (1), a further definition of the Group VIa onium salts are as follows: ##STR71## where M, X and R are as previously defined, and Z is a member selected from the class consisting of -S-, ##STR72## O, Se, CH.sub.2, C.sub.2 H.sub.4, and ##STR73## and R.sup.4 is selected from C.sub.(1-8) alkyl and C.sub.(6-13) aryl.