SILOXANE POLYPHOTOINITIATORS OF THE SUBSTITUTED ACETOPHENONE TYPE

Abstract: An organopolysiloxane photoinitiator having an average of at least two siloxane units, of which at least an average of one siloxane unit per organopolysiloxane molecule has the formula: X a R b SiO (4-a-b/2) (I) wherein a is an integer of 1-3, b is an integer of 0-2 and a plus b equals 1-3; R is C₁-C₁₀ hydrocarbyl or halogen sub­ stituted C₁-C₁₀ hydrocarbyl; and X is a substituted aceto­ phenone photomoiety selected from: where R¹ is any substituent which will not interfere with hydrosilation, n is an integer between 0 and 5 in formulas (II), (IIa), (III), (IIIa), (IV) and (IVa) and between 0 and 4 in formula (III) and (IIIa); m is 0 or 1; R² is alkyl or substituted alkyl; R³ is H, alkyl or aryl; R⁴ is a divalent hydrocarbon group having between 2 and 10 carbon atoms or an alkylene oxy alkylene group; R⁵ is a group selected from H, alkyl, aryl, organosilyl, or the reaction product of an isocyanate esteri­ fication reagent or an etherification reagent with the hydroxyl product formed when R⁵ is H and R⁶ is a trivalent hydrocarbon or hydrocarbon oxyhydrocarbon group. The silicones are prepared by hydrosilation of the cor­ responding olefinically or acetylenically unsaturated aceto­ phenones.

Description: Background of The Invention Many photoinitiators have been developed which are soluble in, and effectively cure, unsaturated organic resins. However, it has been found that such photoinitiators often have limited solubility, and therefore reduced curing effectiveness, in silicones. To overcome this compatibility problem, it has been proposed chemically bond certain photoinittating moieties to silicones. A Japanese patent publication, Xokai No. 34,291/76 describes the use of benzophenone derivatives, such as 4-dimethylamino-4' - (trimethoxysilylbenzophenone, in preparing the silicone compatible photoinitiators Another Japanese patent publication, Sokai No. 71,199/7S, describes the preparation of photoinitiators from the reaction of alkenylsilylbenzophenone and silicones containing silicon hyarides. Japanese patent publicaticn Yokai bc. 50,067/79 and U.S. Patent 4,273,9G7, describe benzoin type photoinitiators attached tc the ends of polydimethylsiloxane through an Si-O-C bond. However, the Si-O-C bond is well know to be hydrolytically unstable. In U.S. Patent 4,391,963 and in co-pending application 505,588, filed June 29, 1983, there are described silicones having benzoin photomoieties bonded thereto through Si-C bonds. These materials are prepared by hydrosilation of alkenyl substituted benzoins. In EPO publication O,O-88,B'42 there are described silicon bonded benzophenone polyphotoinitiators prepared by hydrosilation of an alkenyloxy-substituted benzophenone. Summary of The Invention The present invention relates to novel photoinitiating silicones in which a photomoiety of the substituted acetophenone type is bound to a silicon atom by a Si-C bond. The new photosensitive silicones are conveniently prepared by hydrosilation of corresponding acetophenones having olefinic or acetylenic unsaturation. Detailed Description of The Invention The inventive polyphotoinitiators are organopolysiloxanes having an average of at least two siloxane units, of which at least an average of one siloxane unit per organopolysiloxane molecule has the formula: XaRbSiO (4-a-b)/2 (I) wherein a is an integer of 1-3, b is an integer of 0-2 and a plus b equals 1-3; R is C2-C#0 hydrocarbyl or halogen substituted C1-C10 hydrocarbyl; and X is a substituted acetophenone photomoiety selected from: EMI3.1 where Pl is any substitutent which will not interfere with hydrosilation, n is an integer between 0 and 5 in formulas (II) and (III) and between 0 and 4 in formula (III); m is 0 or 1; R2 is alkyl or substituted alkyl; R3 is H, alkyl or 4 aryl; R is a divalent hydrocarbon group having between 2 and 10 carbon atoms; R5 is a group selected from H, al, organosilyl, or the reaction product of an isocyanate, esterifying reagent or etherification reagent with the hydroxyl product formed when R5 is H. Suitable R groups in the above formula include alkyls such as methyl and ethyl, halogen substituted alkyls such as trifluoropropyl and aryls such as phenyl. Suitable R1 substituents include halo, alkyl, and alkoxy. The R2 groups may be linear, branched or cyclic alkyls or substituted alkyls, including methyl, ethyl, cyclohexyl, cyclooctyl, trichloroethyl, trifluoropropyl and organosilylalkyl such as (trimethylsiloxy)dimethylsilylpropy] and trimethylsilylpropyl. In general the R2 alkyl groups may be substituted with any radical which will not interfere with hydrosilation or the photoinitiating ability of the photcaoiety. It should be understood that combined cyclic structures are intended to be encompassed within the invention. Thus, cyclic acetal or ketal structures may be formed by a carbon-to-carbon linkage of R2 and R4 in formula (fl) or the R2 groups in formula (III). Cycloaliphatic structures may he formed by a carbon-to-carbon linkage cf R2 and R in formula (IV). The resulting structures may be represented by the formulas: EMI4.1 As will be readily apparent to those skilled in the art, both the open and the just described cyclic structures can be readily prepared by the synthetic methods taught herein. The hydrosilation techniques useful for product the inventive polyphotoinitiators are analogous to those described in the aforementioned U.S. Patent 4,391,963 and co-pending applications 505,588 and 528,287, the disclosures of which are incorporated herein by reference. Those procedures may be followed exactly except that the unsaturated benzoin or other photomoieties described in such applications are replaced on a mole-for-mole basis by the unsaturated photontoieties described below. As described in those references, SiR functional silicones may be used to directly hydrosilate the unsaturated photomoiety. Alternatively, SiH functional silanes having polymerizable functionality such as chloro or alkoxy, may be used followed by condensation of the resulting photoinitlating silage with other silanes or silicones. Unsaturated acetophenones suitable as intermediates in the production of inventive polyphotoinitiators can be synthesized by a variety of means including (a) reaction of an alkenyl or alkynyl halide and an alkali alkoxide with an ¯C-oxo-arylacetophenone (e.g. benzil) or an analogous eC-oxo- alkylacetophenone, as exemplified in example 5 of U.S. Patent 4,287,367; (b) transacetalization cf an ,- dialkoxyacetophenone with an unsaturated alcoho t followed by blocking of one of the unsaturated groups as exemplified in Example 6-7; (c) oxidative nitrosation in the presence of excess alcohol of an acetophenone having an unsaturated substituent on the aromatic ring as exemplified in Example 4; or (d) reaction of a benzaldehyde cyanohydrin silylether with a ketone having uncojugated olefinic or acetylenic unsaturation (e.g. methyl allyl ketone or 2-allylcyclohexanone), as exemplified in Example 8 and 9. other synthetic methods for obtaining the unsaturated intermediate photomoieties may occur to those skilled in the art without departing from the invention hereof which is illustrated by the following nonlimiting examples. EXAMPI.E I Benzil zethyl-sllyl-ketal-was prepared by the procedure of Example 5 of U.S. Patent 4,287,367. 2.5 grams of this compound were mixed with 30 grams of a polydimethylsiloxane containing a calculated 4.46x10#4 equivalents of Si-Il per gram of polymer and a calculated molecular weight of about 15,000. The mixture was heated in a flask to 1000C. 0.2 grams of chloroplatinic acid was added, causing an exotherm to 1300 C. Stirring continued at 1300 C for '30 minutes. The product placed in a glass vial overnight remained clear. EXAMPLE 2 The product of example 1 (1 gram) was mixed with 4 grams of a 12,000 molecular weight dimethylpolysiloxane terminated with acryloxypropenyl groups. The acryloxypropenyl terminated silicone is disclosed in example C of co-pending application serial number 575,256 filed January 30, 1984, the disclosure of which is incorporated herein by reference. The resulting clear solution, as a i inch thick slug was exposed to W irradiation of 70,000 microwatts per square centimeter for 20 seconds per side to produce v completely cured polymer mass. EXAMPLE 3 Preparation of A -allyloxymethylacetophenone 4-bromomethylacetophenone was prepared by mixing together 53.6 grams 4-methylacetophenone, 78.8 grams N-bromosuccinimide, 550 ml CCl4 and 0.5 grams benzoyl peroxide. The mixed warm to reflex over d hour period and the reaction monitored via glpc and tic until evidence of starting materials had substantially disappeared. The reaction was cooled, the cooled product isolated by evaporation of solvent and purified by distillation at 105-109 C/0.5mm Hg. 4-allyloxymethylacetophenone was then prepared by mixing 74 grams of purified bromomethylacetcphenone, 300 ml CHC13, 40 mls P.2O and 170 grams allyl alcohol, followed by addition of 30 grams NaOH and 15 rams of a 4CE solution of tetra-n-butyl ammonium hydroxide. The mixture exothermed to reflux and was stirred for 4 hours. The reaction was terminated by addition of 300 mls of water. The organic phase was separated, concentrated by evaporation of solvent and the product purified by distillation at 12O-1350C/0.6rnrn Hg. EXULE 4 Preparation of alpha, alpha-diethoxy-A-allyloxymethyl acetophenone The title product was prepared by mixing the product of example 3 (47.5 grams) with 350ml ethanol and adding 10 grams HC1 gas. The temperature reached about 400C, at which point #2H5 ONO was bubbled into the reaction mixture. The nitrite addition was continued until glpc showed no further change in starting material quantities. The temperature of the mixture was then held at about 600C for 2 hours, cooled and then drowned in a 58 sodium bicarbonate solution. The organic phase was extracted with CH,C12, washed with a dilute sodium hydroxide solution, concentrated by evaporation of solvent and isolated by distillation at l4l-14B#C/0.5iwn Eg. This same reaction can be used to prepare dialkoxy acetophenones from other acetophenone compounds have unsaturated aromatic substitutents such as 4-allyloxyacetophenone and 4-vLnylacetophenone. EXAMPLE 5 5 grams of the silicon hydride functional silicone utilized in example 1 and 0.25 grams of the product of example 4 were weighed into a 3 neck round bottom 25 ml flask equipped with magnetic stirrer and thermometer. The temperature of the cloudy mixture was brought to 1000C and 1 drop (approximately 0.1 gl of a 2% chloroplatinic acid solution in butyl acetate was added. The addition produced an exotherm and a clear solution. After 15 minutes the reaction was terminated. The resulting product remained clear on cooling and was soluble in dimethyl silicones having 2,5 and 8% methylvinyl siloxane repeat units. 208 by weight mixtures of the polyphotoinitiator product in such vinyl silicones cured when exposed to UV irradiation of 70,000 iaicrowatts/square centimeter for two minutes. EXAMPLE 6 Diallyoxyacetophenone was prepared as follows. Diethoxyacetophenone (104 grams) and 300 ml allyl alcohol were stirred and heated with 8 grams p-toluene sulfonic acid H 20. As ethyl alcohol was removed via a Dean-Stark trap another 109 mls allyl alcohol was added. The reaction was monitored by glpc until completion. The mixture was then cooled and 500 mls of saturated sodium, bicarbonate solution was added. The organic fraction was separated and the aqueous fraction extracted with hexane. The organic fractious were then combined, dried, filtered and concentrated. The product was purified by distillation at l25-130 C/0.9 mm Hg. EXAMPLE 7 Into a 25 ml 3 neck round bottomed flask eipped with a thermometer and stirrer replaced 1 grain of ciallylcxyace- tophenone and .63 grams of pentamethyldisiloxane. The flask was placed in an oil bath at 85 DO. When the temperature reached 85 C, 0.5 grams of a 28 chioroplatinic acid solution were added. After stirring for 5 minutes, 2.2 grams of an approximately 1,000 mclecular weight dimethylsilicone terminated with silicon hydride (0.002eq.H/grain) were added along with an additional 0.05 grams of chloroplatinic acid solution. An exotherm from 110 C to 12500 was observed. After about 5 minutes the reaction was allowed tc cool producing a dark fluid product. This product was soluble in a 70,000 molecular weight silicone containing 88 by mole methylvinylsiloxane units. A 20% solution of the product in this vinyl silicone cured a k inch slug when exposed to UV irradiation of 70,000 microwatts per square centimeter for 2 minutes. The solubility of this low molecular weight silicone photoinitiator in high molecular weight silicones was particularly surprising since a benzoin type photoinitiator prepared from the same 1,000 molecular weight silicone by the method of U.S. Patent 4,391,963 was not soluble in other higher molecular weight silicones. Example 8 Benzaldehyde, 19.6gms; trimethylsilylcyanide, 20.4gums; and 100 ml acetonitrile were added to a round bottomed flask equipped with condensor, stirrer and argon gas inlet. Two min. after the addition, lg anhydrous stannous chloride was added. The reaction was exothermic. Stirring was continued for 1 hr. after which the reaction was quenched by pouring the solution into a separatory funnel containing ice water. The crude product was extracted into methylenedichloride, dried over MgSOt and Nazi03 and subjected to vacuum distillation at 1140C and 0.28mm Hg. A moisture free apparatus consisting of a 500 ml 3-neck round-bottoined flask, three dropping funnels, a gas inlet tube and a stirring bar was set up and purged thoroughly with argon. 12 lug diisopropylamine and 250 ml tetrahydrofuran were added to the flask and the resulting solution cooled to 7800. 120 ml s-butyl lithium in hexane (1.25M) was added and the mixture stirred at -7 & C for an hour. 20.5g of the product of the previous paragraph were then added over 30 min. 15.4 of 2-allylcyclohexanone was then added and the solution maintained at 7800 for 1 hr. After the mixture had reached room temperature, 10 ml H20 was added. The mixture was then poured into a liter of water and extracted with benzene. The benzene layer was dried over MgSO4 and evaporated to give the trimethylsilyl ether of l-benzoyl-2-allylcyclohexanol. 15 grams of the silcone hydride functional dimethyl silicone used in example 2 was reacted as in example 2 with 1.4 grams of the trimethylsilyl ether of l-benzcyl-2-allylcyclohexanol. 0.3 grams of the resulting product was then dissolved in 3 grams of a silicone containing 8E methylvinylcyclohoexanone units. A thin film of this mixture was exposed to W irradiation of /0,000 microwatts per square centimeter for 2 minutes producing a cured clear film. EXAMPLE Q Example 8 may be repeated substitutins at equivalent amount of methyl allyl ketone for the 2-allylcnclonexâr.one utilized in that example. After the hydrosilation, the resulting polyphotoinitiator product will be represented by formula (I) where X is: EMI12.1 EXAMPLE 1C If Example 6 is repeated substituting an excess of a monoallyl ether of glycerin for the allyl alcohol in Example 6, a cyclic unsaturated acetal product is formed which may subsequently be hydrosilated as in Example 7 to give a polyphotoinitiator product of the invention. The l-allyl ether of glycerin may thus be utilized to produce a photoinitiator of the invention where X in formula (I) above is EMI12.2 The 2-allyl ether of glycerin can thus be utilized to give a photoinitiator of the invention where X is EMI13.1 Among the many variations of the above procedures which can be employed without departing from the Invention hereof are the use of mixed saturated and unsaturated alcohols in the procedure of Example 6; substitution of acetylenic reagents for the corresponding clefinic reagents (e.s., propargyl bromide or alcohol for allyl bromIde or alcohol it Examples 1, 3 and 6); blocking of one of the unsaturated groups of the diallyl product of Example 6 with other olefinically reactive reagents such as trimethylsilane, hydrogen or halogens; and acid catalyzed cleavage of the trimethylsilyl ether product of Example 8 to the corresponding alcohol, with optional subsequent esterificatiot, etherifi- cation or reaction with other hydroxy reactive materials such as isocyanates or epoxes. While the primary use of the inventive compounds is in the photocuring of vinyl or acrylic (i.e., acrylate, methacrylate, etc.) functional silicones, other compounds with free radical cureable functionality sich as organic compounds with vinztl, acrylic, maleic, or itaconic functionalities may also be photocured with the inventive compounds as well.

Claims: CLAIMS 1. An organopolysiloxane photoinitiator having an average of at least two siloxane units, of which at least an average of one siloxane unit per organopolysiloxane molecule has the formula: XaRbSiO(4-a-@)/2 (I) wherein a is an integer of 1-3, b is an integer of 0-2 and a plus b equals 1-3; R is C1-C10 hydrocarbyl or halogen substituted Cl-C10 hydrocarbyl; and X is a substituted acetophenone photomoiety selected from: EMI14.1 where R1 is any substituent which will not interfere with hydrosilation, n is an integer between 0 and 5 in formulas (II), (IIa), (III) , (IIIa), (IV) and (IVa) and between 0 and 4 in formula (III) and (ITla); m is O or 1; R2 is alky# or substituted alkyl; R3 is fl, alkyl or aryl; R4 is a divaZent hydrocarbon group having between 2 and 30 carbon atoms or an alkylene oxy alkylene group; R5 is a group selected from H, alkyl, aryl, organosilyl, or the reaction product of an isocyanate esterification reagent or an etherification reagent with the hydroxyl product formed when R5 is H and R6 is a trivalent hydrocarbon or hydrocarbon oxyhydrocarbon group. 2. A photoinitiator as in Claim 1 where R is alkyl, substituted alkyl or aryl. 3. A photoinitiator as in Claim 1 where R1 is halo, alkyl or alkoxy. 4. A photoinitiator of Claim 1 where n is 0. 5. A photoinitiator of Claim 1 where X is selected from formulas IT and III and R is alkyl. 6. A. photoinitiator of Claim 1 where R4 is propylene or propenylene. 7. A photoinitiatoi of Claim 1 wherein X has the structure of formula Tia. 8. A photoinitiator of Claim 1 wherein X has the structure of formula Ill and m is 3. 9. A photoinitiator of Claim 1 wherein X has the structure of formula Ilfa, 10. A photoinitiator of Claim 1 wherein X has the structure of formula IV and R5 is organosilyl. 11. The method of curing a free radical curable compound comprising subjectiary to actinic radiation a composition of said compound and a photoinitiator as in Claim 1. 12. The method of Claim 11 wherein said curable compound is a silicone. 13. The method of Claim 12 wherein said curable silicone compound is an acrylic of vinyl functional silicone. 14. A composition comprising a photoinitiator as in Claim 1 and a free radical curable compound. 15. The composition of Claim 14 wherein said curable compound is a silicone. 16. The composition of Claim 15 wherein said curable silicone is an acrylic or vinyl functional silicone. 17. A photoinitiator of Claim 1 in which Rê is an alkyl or alkenyl group substituted with an organosilyl group. 18. A photoinitiator as in Claim 17 where R2 is trimethyl silylpropyl or (trimethylsiloxy)dimethylsilylpropyl.

Inventors: FABRIZIO, LOUIS F., JACOBINE, ANTHONY F., LIN, SAMUEL Q. S.
Applicants: LOCTITE CORPORATION
Application year: 1985
Main classification: C08F2
IPC codes: C08G77, G03F7, C08F2