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Applications: Free Radical InitiatorsPhotoinitiators: ClassificationA photoinitiator is a compound especially added to aformulation to convert absorbed light energy, UV or visiblelight, into chemical energy in the form of initiating species,viz., free radicals or cations. Based on the mechanism bywhich initiating radicals are formed, photoinitiators aregenerally divided into two classes: Type I photoinitiators undergo a unimolecular bond cleavage upon irradiation to yield free radicals. Type II photoinitiators undergo a bimolecular reactionwhere the excited state of the photoinitiator interactswith a second molecule (a coinitiator) to generate freeradicals.UV photoinitiators of both Type I and Type II are available.However, visible light photoinitiators belong almostexclusively to the Type II class of photoinitiators. Table Isummarizes the various classes of available Type I and TypeII photoinitiators and their common applications.Table I: Common Applications for Different Classes of PhotoinitiatorsUV-PhotoinitiatorsType I PhotoinitiatorsPhotoinitiatorClassApplicationWood alkoxy- a-Hydroxy- a-AminoAcylacetoalkylalkylphosphinephenones phenones phenonesoxidesXPaper coatingsXPrinting platesXOffset inksXBenzoThiophenones/ xanthones/ TitanocenesaminesaminesXXClear coatings(on metal,wood, plastic)VisiblePhotoinitiatorsType IIXXX2XX1XXXXXScreen inksX3XXPigmentedcoatingsXWhite lacquersX4Photo resistsX3XXXX(1) In combination with benzophenone. (2) Only systems of high reactivity. (3) Partially in combination with thioxanthones. (4) Thin layers only.This chart is reprinted with permission from SITA Technology Ltd.aThe Link to All Your Polymer Needs5
Applications:Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption SpectraFor photoinitiation to proceed efficiently, the absorption bandsof the photoinitiator must overlap with the emissionspectrum of the source and there must be minimalcompeting absorption by the components of the formulationat the wavelengths corresponding to photoinitiatorexcitation. For the initial selection of a photoinitiator in yourapplication, viz., one with excitation wavelengths that lie inthe emission spectrum of your UV source, as well as in theabsorption window of your formulation, information about thephotoinitiator absorption spectrum is essential.To aid in this initial selection, UV absorption spectra of 47commonly used radical and cationic photoinitiators (seeTable I) are displayed in this section. Approximately 100Table 12,489-3C7,240-440,807-7D3,173-722,710-2D11,050-76 Spectra were recorded on a Perkin Elmer UV/Vis Lambda 2spectrophotometer using Perkin Elmer ComputerizedSpectroscopy Software 4.01. Concentrations are expressedas % weight of solute in volume of solvent. The solventused was A.C.S. spectrophotometric grade methyl alcohol.For comparison purposes, the emission spectrum of amedium pressure mercury lamp, the most widely usedenergy source, is shown as the last figure.Commonly Used Radical and Cationic Photoinitiators whose UV Absorption Spectra areDisplayed in this Section. (Click on the photoinitiator name coded red to view the UVspectrum. Click on the product number coded blue to link to the product document sheeton the Sigma-Aldrich Web site.)Cat. No. tional substituted acetophenones and benzophenonesthat are potential photoinitiators are available from Aldrich;search our product database at www.sigma-aldrich.com.Acetophenone, 99%Anisoin, 95%Anthraquinone, 97%Anthraquinone-2-sulfonic acid, sodium saltmonohydrate, 97%(Benzene) tricarbonylchromium, 98%Benzil, 98%Benzoin, sublimed, 99.5 %Benzoin ethyl ether, 99%Benzoin isobutyl ether, tech., 90%Benzoin methyl ether, 96%Benzophenone, 99%Benzophenone/1-Hydroxycyclohexyl phenylketone, 50/50 ide, sublimed, 98%4-Benzoylbiphenyl, enone, 97%4,4'-Bis(diethylamino)benzophenone, 99 %4,4'-Bis(dimethylamino)benzophenone, 98%Camphorquinone, 98%2-Chlorothioxanthen-9-one, hate, 98%Dibenzosuberenone, 97%2,2-Diethoxyacetophenone, 95%4,4'-Dihydroxybenzophenone, 99%Polymer Products from AldrichCat. itiator2,2-Dimethoxy-2-phenylacetophenone, 99%4-(Dimethylamino)benzophenone, 98%4,4'-Dimethylbenzil, 97%2,5-Dimethylbenzophenone, tech., 95%3,4-Dimethylbenzophenone, 99%Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide/2-Hydroxy-2-methylpropiophenone, 50/50 blend4'-Ethoxyacetophenone, 98%2-Ethylanthraquinone, 97 %Ferrocene, 98%3'-Hydroxyacetophenone, 99 %4'-Hydroxyacetophenone, 99%3-Hydroxybenzophenone, 99%4-Hydroxybenzophenone, 98%1-Hydroxycyclohexyl phenyl ketone, 99%2-Hydroxy-2-methylpropiophenone, 97%2-Methylbenzophenone, 98%3-Methylbenzophenone, 99%Methybenzoylformate, one, 98%Phenanthrenequinone, 99 %4'-Phenoxyacetophenone, 98%Thioxanthen-9-one, 98%Triarylsulfonium hexafluoroantimonate salts,mixed, 50% in propylene carbonateTriarylsulfonium hexafluorophosphate salts,mixed, 50% in propylene carbonatea
Applications:Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)A1,070-1 Acetophenone, 99%A8,840-9 Anisoin, 95%OC CH3OCH O3CH COCH3OH0.0224 %0.0040 %0.0011 %0.0014 %12,324-2 Anthraquinone-2-sulfonic acid, sodium saltmonohydrate, 97%A9,000-4 Anthraquinone, 97%OOOS ONaOOaH O2O0.0010%0.0033 %0.0004 %0.0006 %The Link to All Your Polymer Needs 7
Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)11,931-8 (Benzene) tricarbonylchromium , 98%B515-1Benzil, 98%1O OC C.8OCCrCOCO.8.60.0012 %.40.0029 %.6AbsorbanceAbsorbance0.0023 %0.0011 0022044039,939-6 Benzoin, sublimed, 99.5 %CH.8 280300OCCH C.8OH.2.2320340360Nanometers4400.0019 %.4300420380Polymer Products from Aldrich4004204400.0027 %.6.4280400Absorbance0.0017 %260380OCH CH2 30.0056 %240320340360NanometersOAbsorbance826017,200-6 Benzoin ethyl ether, 400420440a
Applications:Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)19,578-2 Benzoin isobutyl ether, tech., 90%.8B870-3Benzoin methyl ether, 96%OOCH CCH CO CH CHCH23CH3OCH.83.6.60.0069 %.40.0043 %AbsorbanceAbsorbance0.0110 %0.0020 0400420022044024026028030038040042044040,562-0 Benzophenone/1-Hydroxycyclohexylphenyl ketone, 50/50 blendBenzophenone, 99%OOC.8320340360NanometersC.8OCOH.60.0012 %a0.0015 4204400.0150 %.6AbsorbanceAbsorbance0.0030 %0220240260280300320340360Nanometers380400420The Link to All Your Polymer Needs440 9
Applications:Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)26,246-3 3,3',4,4'-Benzophenonetetracarboxylicdianhydride, sublimed, 98%O.8B1,260-1 4-Benzoylbiphenyl, 99%OOOCOCOOOAbsorbance.60.0030 %0.0031 %0.0010 %0.0004 4040,564-7 ne, 97%16,032-6 4,4'-Bis(diethylamino)benzophenone, 99 %O.8ONCCH2C.8N(CH )32CH CH2 30.0035 %0.0020 %0.0020 %.6AbsorbanceAbsorbance.60.0008 %.4.4.2.2CH CH3 2CH CH N3 2022010 240260280300320340360Nanometers380Polymer Products from Aldrich4004204400220240260280300OCH CH2 3NCH CH2 3C320340360Nanometers380400420440a
Applications:Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)12,489-3 Camphorquinone, 98%14,783-4 4,4'-Bis(dimethylamino)benzophenone, 98%CHCH3.8.8OR CH3O0.0271 %AbsorbanceAbsorbance0.0008 %or3.60.0031%.6R HR CHR HR0.0071 anometers38040042044040,807-7 e, 98%C7,240-4 2-Chlorothioxanthen-9-one, 98%OClFeS0.0024 %0.0007 %.2.2a280300320340360Nanometers3804004204400.0055 %0.0027 %.42606.6.4240PFAbsorbanceAbsorbance.60220CH3CH 0The Link to All Your Polymer Needs440 11
Applications:Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)D3,173-7 Dibenzosuberenone, 97%22,710-2 2,2-Diethoxyacetophenone, 95%OC.8.8O0.0016 %0.0005 %0.0014 100 %.6.40220OCH CH2 3AbsorbanceAbsorbance.6OCH CH2 3CH0220440D11,050-7 4,4'-Dihydroxybenzophenone, 11-8 2,2-Dimethoxy-2-phenylacetophenone, 99%1OHOCO OCH3OHC COCH.80.0036 %0.0009 %12 0.0011 %.4.4.2.2240260280300320340360Nanometers380Polymer Products from Aldrich4004204400.0020 0340360Nanometers380400420440a
Applications:Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)14,934-9 4-(Dimethylamino)benzophenone, 98%14,670-6 4,4'-Dimethylbenzil, 97%1O OCH.8C C3CH3.8.60.0043 %0.0030 %0.0009 %AbsorbanceAbsorbance.6.40.0010 s3804004200220440D14,966-7 2,5-Dimethylbenzophenone, tech., 967-5 3,4-Dimethylbenzophenone, 99%OCHCH3.8O.8CHCC33CH3.6.60.0015 %0.0013 %.4.4.2.20220a0.0039 %AbsorbanceAbsorbance0.0296 0260280300320340360Nanometers380400420440The Link to All Your Polymer Needs 13
Applications:Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)40,566-3 Diphenyl(2,4,6 trimethylbenzoyl)phosphine oxide2-Hydroxy-2-methylpropiophenone 50/50 blend27,571-94'-Ethoxyacetophenone, 98%CH3O OCH3.8CPOC CHCH3OCH CH2 3O OHC.63.8CCH3CH3.60.0019 %.40.0044 %AbsorbanceAbsorbance0.0223 %0.0009 00220440E1,220-6 Ethylanthraquinone, 97 errocene, 98%1OFeCH CH2 3.8.8O.2.2 0.0028 %.4.4140.0065 %AbsorbanceAbsorbance0.0005 %0220.60.0018 %.6240260280300320340360Nanometers380Polymer Products from s380400420440a
Applications:Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)32,810-33'-Hydroxyacetophenone, 99 %27,856-44'-Hydroxyacetophenone, 99%1OC CH3OC CH3.8OH.8OH.6Absorbance0.0007 %0.0009 %.4.4.2.202200.0048 %Absorbance0.0026 002204403-Hydroxybenzophenone, 04404-Hydroxybenzophenone, 98%1OOHOCHOC.8.80.0030 %0.0013 %.4.4.2.20220aAbsorbanceAbsorbance0.0011 %240260280300320340360Nanometers3804004204400.0051 he Link to All Your Polymer Needs440 15
Applications:Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)40,561-240,565-51-Hydroxycyclohexyl phenyl ketone, 99%2-Hydroxy-2-methylpropiophenone, 97%1OCOH.8OHCC0.0047 %0.0008 s3804004200.0053 %.6.424033AbsorbanceAbsorbance0.0019 anometers3804004204403-Methylbenzophenone, 99%OOCCCH.8CH0.0122 %0.0013 %16 0.0012 %.4.4.2.2240260280300320340360Nanometers380Polymer Products from Aldrich4004204400.0071 20340360Nanometers380400420440a
Applications:Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)M3,050-740,563-9Methybenzoylformate, 98%.8O ne, 98%CH S3OCH3OCHCC3NOCH3.8.6.60.0025%0.0052 %AbsorbanceAbsorbance0.0625 %0.0014 rs3804004200220440Phenanthrenequinone, 99 404'-Phenoxyacetophenone, 98%1OOOOC CH3.8.80.0049 %0.0028 0.0032 %0.0008 0340360Nanometers380400420The Link to All Your Polymer Needs440 17
Applications:Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)T3,400-240,722-4Thioxanthen-9-one, 98%Triarylsulfonium hexafluoroantimonate salts,mixed, 50% in propylene carbonate1OS0.0016 %0.0005 %SbF60.0108 %.6AbsorbanceAbsorbance.60.0048 eters380400420440Triarylsulfonium hexafluorophosphate salts,mixed, 50% in propylene carbonateS.8SPF60.0223 %Absorbance.60.0039 %.4.2022018 240Polymer Products from Aldrich260280300320340360Nanometers380400420440a
Applications: Free Radical InitiatorsPhotoinitiators: UV Absorption Spectra (continued)Emission spectrum of a medium pressure mercury arc lampSPECTROPHOTOMETRIC GRADE SOLVENTS Excellent for applications requiring-High purity -UV transparecy-Low residue on evaporation Rigorously analyzed during and after production, andduring packaging to ensure high purity Once packaged, leakage and breathing problems areeliminated because we use the Sealed for Quality system4-Liter sizes come in standard amber glass bottles. Thesebottles have a PVC shrink band around the neck to provideadditional closure integrity and tamper evidence.aThe Link to All Your Polymer Needs19
that are potential photoinitiators are available from Aldrich; search our product database at www.sigma-aldrich.com. Spectra were recorded on a Perkin Elmer UV/Vis Lambda 2 spectrophotometer using Perkin Elmer Computerized Spectroscopy Software 4.01. Concentrations are expressed as % weight of solute in volume of solvent. The solvent
