WO2007092935A1

WO2007092935A1 - Hydroxyalkylaminoalkylthioxanthones

Info

Publication number: WO2007092935A1
Application number: PCT/US2007/061866
Authority: WO
Inventors: Mahmood Sabahi; Eric L. Williams; Wenfeng Kuang; Charles A. Brady
Original assignee: Albemarle Corporation
Priority date: 2006-02-08
Filing date: 2007-02-08
Publication date: 2007-08-16

Abstract

Novel, UV radiation hydroxyalkylaminoalkylthioxanthone photoinitiators are disclosed having a hydroxyalkylaminoalkyl group, which can be in the third conjugated ring at the ortho or meta positions thereof. The hydroxyalkylaminoalkyl group comprises a tertiary amine and at least one hydroxy group in proximity to one another such that the hydroxyalkylaminoalkylthioxanthone can increase the rate of polymerization of a photo-curable compound and the polymerized product can be formed into a cured film substantially free of extractable residues.

Description

HYDROXYALKYLAMINOALKYLTHIOXANTHONES

FIELD OF THE INVENTION

[0001] The invention provides novel ultraviolet (UV) radiation photoinitiators that upon inclusion in a photopolymerizable system result in polymers having no extractable components left in the polymer matrix. The compounds react with monomer, pre-polymer, or oligomer. When used alone or in conjunction with maleimides, the compounds of the present invention form pre-polymers or oligomers that polymerize on exposure to UV radiation without requiring any other additives, i.e., self-initiating pre-polymers or oligomers. The present invention also provides such self-initiating pre-polymer or oligomers, as well as methods of photopolymerization employing these self-initiating pre-polymers or oligomers.

DESCRIPTION OF RELATED ART

[0002] Ethylenically unsaturated compounds can be polymerized by exposure to radiation, typically ultraviolet light, in the presence of a photoinitiating system. Typically, the photoinitiating system includes (1) a compound capable of initiating polymerization of the ethylenically unsaturated compound upon exposure to radiation (a "photoinitiator") and optionally (2) a coinitiator or synergist, that is, a molecule which serves as a hydrogen atom donor. The coinitiators or synergists are typically alcohols, tertiary amines, amides, or ethers which have labile hydrogens attached to a carbon adjacent to a heteroatom (oxygen, nitrogen, sulfur, and the like). Currently commercially available photoinitiators include benzophenones and derivatives thereof, such as thioxanthone derivatives.

[0003] Maleimides, and in particular N-aliphatic and ortho-substituted ("twisted") N-aromatic maleimides have been investigated as comonomer-photo initiators of UV-curable systems. Ultraviolet curable maleimide pre-polymers offer a key advantage of having no extractable residues in their cured films. Although these pre-polymers cure more slowly than most common systems, their cure rate can be accelerated by the addition of conventional photoinitiators like thioxanthones. Unfortunately, adding conventional photoinitiators results in a cured film with extractable residues.

[0004] US Patent 6,555,593, which is incorporated herein by reference, describes photopolymerizable compositions comprising at least one radiation curable compound, at least one maleimide which is capable of initiating the photopolymerization of the radiation curable compound, a sensitizer/photoinitator comprising at least one thioxanthone compound and at least one coinitiator or synergist as a hydrogen atom donor or electron donor. The '593 patent describes the synergistic effect that occurs when the sensitizer/photoinitiator is used in conjunction with the maleimide in the presence of the hydrogen atom donor, with dramatically increased rates of polymerization of typical photo-curable systems, as compared to rates obtained using the same photo-curable system with either maleimide with a hydrogen atom donor or the sensitizer with a hydrogen-atom donor as the initiating system.

[0005] As described in the '593 patent, the maleimide component can be substantially consumed during initiation and photopolymerization (incorporated into the polymer structure) when a sensitizer/photoinitiator is not used. Unfortunately, adding a sensitizer/photoinitiator results in a cured film with extractable residues. This is disadvantageous in that, for example, the exudation and migration of extractable residues from the film could limit use of the film. For example, the presence of extractable residues could prevent use of the film in food packaging.

[0006] What is needed is a chemically bindable photoinitiator that, in conjunction with a maleimide compound, provides an increased rate of photopolymerization of an ethylenically unsaturated polymerizable compound with formation of a cured film that is substantially free of extractable resins.

SUMMARY OF THE INVENTION

[0007] Accordingly, the present invention provides novel thioxanthones having a hydroxyalkylaminoalkyl substituent suitable as a chemically bindable photoinitiator for UV radiation curing. The hydroxyalkylaminoalkyl group comprises a tertiary amine and at least one hydroxy group in proximity to one another such that the hydroxyalkylaminoalkylthioxanthone, when used in conjunction with a maleimide, can increase the rate of polymerization of a photo- curable compound and the polymerized product can be formed into a cured film substantially free of extractable residues. The hydroxyalkylaminoalkyl group may be placed at any position on the phenyl rings, including without limitation the 2- and 4-positions.

[0008] In addition to these photoinitiators, a novel co-product, vinylthioxanthone, which is formed during their synthesis, is also disclosed. The vinyl group of this thioxanthone derivative provides a chemical handle for functionalizing the thioxanthone derivative or for reacting the vinylthioxanthone directly into a monomer, pre-polymer or oligomer via free-radical reaction, anionic, or cationic polymerization. [0009] The present invention also provides photopolymerizable compounds having at least one ethylenically unsaturated double bond, and at least one hydroxyalkylaminoalkylthioxanthone group; photopolymerizable compounds having at least one ethylenically unsaturated double bond, at least one maleimide group capable of initiating photopolymerization of said photopolymerizable compound, and at least one hydroxyalkylaminoalkylthioxanthone group to sensitize initiation of the photopolymerizable compound by the maleimide; and methods of photopolymerizing such photopolymerizable compounds.

DESCRIPTION OF THE FIGURES

[0010] The following figures form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these figures in combination with the detailed description of specific embodiments presented herein.

Figure 1 illustrates the improved photopolynieric efficiency of 2-[N-methyl-N-(2- hydroxyethyl)]ethylthioxanthone (MHAT) as compared to isopropyl thioxanthone.

Figure 2 illustrates the improved polymerization rate exhibited by an oligomer end- capped with MHAT.

DETAILED DESCRIPTION OF THE INVENTION

[0011] The novel photoinitiators of the present invention include compounds according to

Structure (I) below: e (T)

wherein: each Ri is independently selected from the group consisting of hydrogen, halogen, Cr Cj₈ alkyl, C₃-C₆ cycloalkyl., and C₁-Ci₈ alkoxy;

R₂ is selected from the group consisting OfC₂-Ci i alkyl;

R₃ is selected from the group consisting of hydrogen, Ci-C₈ alkyl, Ci-C₈ cycloalkyl, Ci to C]₂ alkoxy; and,

R₄ is selected from the group consisting of C₂ to Cn alkyl.

[0012] Compounds of the present invention include compounds according to Structure (II) and Structure (III) below:

wherein:

R is selected from the group consisting of hydrogen, Ci-C₈ alkyl and Ci-C₈ cycloalkyl; n ranges from 1 to 10; and m ranges from 1 to 10; and, Structure CIID

wherein: n ranges from 1 to 10; m ranges from 1 to 10; and k ranges from 1 to 10.

[0013] In general, the hydroxyalkylaminoalkylthioxanthones of the present invention are prepared by reacting a bromoalkylthioxanthone with a hydroxyalkylamine, in the presence of an inorganic base like a carbonate, such as potassium carbonate, potassium bicarbonate, sodium carbonate, sodium hydrogen carbonate, and the like, or an organic base like a tertiary amine, such as triethylamine, in a sufficient amount of a non-nucleophilic polar solvent like acetonitrile (at refluxing temperature) to ensure dissolution of the reactants, In addition to acetonitrile, other solvents may be employed, such as dioxane, dimethylsulfoxide, dimethylacetamide, dimethylformamide, N-methylpyrrolidione, and the like. Stoichiometric amounts of the reactants may be used, or alternatively, up to an excess of about two molar equivalents of the hydroxyalkylamine. The amount of carbonate or tertiary amine added to the reaction mass ranges from about a molar equivalent to up to about an excess of two molar equivalents. The following scheme illustrates the general reaction pathway.

.,NH ,OH

wherein R₁, R₂, R₃ and R₄ are as previously described in regard to Structure (I). Variations in the hydroxyalkylaminoalkylthioxanthone structure may be achieved by varying Ri and R₂ on the bromoalkylthioxanthone and R₃ and R₄ on the hydroxyalkylamine.

[0014] After refluxing the reaction mass for about 1 to about 10 hours under a nitrogen atmosphere, the reaction mass is allowed to cool to about room temperature after which the hydroxyalkylaminoalkylthioxanthone is isolated as a solid product by conventional means. [0015] During the process of synthesizing the hydroxyalkylaminoalkylthioxanthone, an intermediate is formed, which can be isolated and used as a photoinitiator by incorporating the intermediate directly into a pre-polymer or oligomer, or used to synthesize various substituted thioxanthone derivatives. The structure of the intermediate, a vinylthioxanthone, is shown in Structure (VI) below:

Structure (VI)

wherein: each Ri is independently selected from the group consisting of hydrogen^ halogen, C₁- Ci8 alkyl, C₃-C₆ cycloalkyl, and Cj-Cis alkoxy; and

R5 is selected from the group consisting OfC₁-Ci_O alkyl.

[0016] The following examples illustrate the preparation of hydroxyalkylaminoalkylthioxanthones.

Example 1:

Preparation of 2-[N-methyl-N-(2-hydroxyethyl)]ethylthioxanthone (MHAT):

[0017] A mixture of bromoethylthioxanthone (100 g, 0.31 mol), 2-(methylamino)ethanol (30 g, 0.4 mol), sodium hydrogen carbonate (sodium bicarbonate) (39 g, 0.46 mol), sodium iodide (5 g, 0.03 mol), and acetonitrile (600 mL) was refluxed for 5 hrs under nitrogen. The purpose of the sodium iodide is to act as a catalyst and speed reaction rate; however, the reaction would proceed in its absence. The reaction mixture was cooled to room temperature and ethyl acetate (500 mL) was added. The organic phase was extracted with 10% HCl solution (3x100 mL) and then the pH of the aqueous solution was adjusted to 11 by addition of dilute sodium hydroxide. The organic layer was separated and the aqueous phase was extracted with ethyl acetate (3x100 mL) and the combined organic phase was dried and distilled under reduced pressure to afford the desired product, 2-[N-methyl-N-(2-hydroxyethyl)]ethylthioxanthone (MHAT), as a yellow solid. The structure, confirmed by NMR and mass spectrometry, is shown below as Structure (IV):

Example 2:

[0018] The process of Example 1 was performed again with modification. Triethylamine was used in place of sodium hydrogen carbonate. After refluxing for more than five hours, the reaction mixture was evaporated to dryness under reduced pressure. The residue was slurried in acetone and filtered. The filtrate was concentrated under reduced pressure to afford MHAT as a yellow solid.

Example 3:

Preparation of 2-[N,N-Bis(2-hydroxyethyl)]ethylthioxanthone (DHAT):

[0019] The process of Example 1 was performed again with modification.

N-methylhydroxylamine was replaced with diethanolamine.

2-[N₉N-B is(2-hydroxyethy I)] ethylthioxanthone (DHAT) was afforded as a yellow solid. The structure, confirmed by NMR and mass spectrometry, is shown below as Structure (V):

Structure (V)

[0020] The hydroxyalkylaminoalkylthioxanthones of the present invention share the unique features of having an alkylamino moiety that will function as a synergist for thioxanthone, having a hydroxyl group that will react with monomer or pre-polymer and will become part of the polymer matrix, and producing a pre-polymer or oligomer, when used in conjunction with maleimides, acrylates, or vinyl ethers, that polymerizes upon exposure to UV light without the need for any other additive (i.e., self-initiating pre-polymer or oligomer) and produces a polymer that is substantially free of extractable components.

[0021] Accordingly, a photopolymerizable composition of the present invention comprises a chemically bound synergist component having an alkylamino moiety that serves as a hydrogen atom donor, wherein the chemically bound synergist component is derived from the hydroxyalkylaminoalkylthioxanthones described above. The composition can include about 0.01 to about 20 percent by weight, or about 0.01 to about 10 percent by weight synergist (i.e., hydroxyalkylam inoalkylthioxanthone) component.

[0022] The photopolymerizable compositions generally include monomers and oligomers derived from acrylic and^' methacrylic acid, vinyl ethers, or N-vinyl compounds, optionally dispersed or dissolved in a suitable solvent that is copolymerizable therewith, and mixtures thereof, which are photopolymerizable when exposed to a source a UV radiation, particularly free radical polymerizable systems. As will be appreciated by the skilled artisan, the photopolymerizable compounds can be monofunctional, or can include two or more polymerizable ethylenically unsaturated groupings per molecule.

[0023] Exemplary photopolymerizable compounds or precursors include, but are not limited to, reactive vinyl monomers, including acrylic monomers, such as acrylic and methacrylic acids, and their amides, esters, salts and corresponding nitriles. Suitable vinyl monomers include, but are not limited to, methyl acrylate, ethyl acrylate, tert-butyl acrylate, isooctyl acrylate, methyl methacrylate, ethyl methacrylate, 2-ethylhexyl methacrylate, butylacrylate, isobutyl methacrylate, the corresponding hydroxy acrylates, i.e., hydroxy ethylacrylate, hydroxy propylacrylate, hydroxy ethylhexyl methacrylate, glycol acrylates, i.e., ethylene glycol dimethacrylate, hexamthylene glycol dimethacrylate, the allyl acrylates, i.e., allyl methacrylate, diallyl methacrylate, the epoxy acrylates, i.e., glycidyl methacrylate, and the aminoplast acrylates, i.e., melamine acrylate. Others, such as vinyl acetate, vinyl and vinylidene halide and amides, i.e. methacrylamide, acrylamide, diacetone acrylamide, vinyl and vinylidene esters, vinyl and vinylidene ketones, butadiene, vinyl aromatics, i.e., styrene, alkyl styrenes, halostyrenes, alkoxystyrenes, divinyl benzenes, vinyl toluene, and the like are also included. Pre-polymers including acrylated epoxides, polyesters, and polyurethanes, and are typically combined with a suitable monomer for viscosity control. Suitable vinyl ethers include, but are not limited to, n-propyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, t-butyl vinyl ether, t-amyl vinyl ether, cyclohexyl vinyl ether, 2-ethylhexyl vinyl ether, dodecyl vinyl ether, octadecyl vinyl ether, 2-chloroethyl vinyl ether, ethylene glycol butyl vinyl ether, (4- vinyloxy)butyl benzoate, ethylene glycol divinyl ether, diethylene glycol divinyl ether, triethylene glycol divinyl ether, tetraethylene glycol divinyl ether, butane- 1,4-diol-di vinyl ether, hexane-l,6-diol-divinyl ether, cyclohexane-l,4-dimethanol-divinyl ether, di(4-vinyloxy)butyl isophthalate, di(4-vinyloxy)butyl glutarate, di(4-vinyloxy)butyl succinate, trimethylolpropane trivinyl ether, 2-hydroxyethyl vinyl ether, 4-hydroxybutyl vinyl ether, 6-hydroxyhexyl vinyl ether, cyclohexane-l,4-dimethanol-monovinyl ether, diethylene glycol monovinyl ether, 3- aminopropyl vinyl ether, 2-(N,N-diethylamino)ethyl vinyl ether, urethane vinyl ether, polyester vinyl ether and the like.

[0024] The photopolymerizable compounds may be polymerized to form homopolymers or copolymerized with various monomers.

[0025] The photopolymerizable compound can be present in the compositions of the invention in amounts from about 1.0 to about 99.8 percent by weight, based on the total weight of the composition. [0026] The photopolymerizable compositions of the present invention may include a maleimide component. Maleimide compounds suitable for use as the maleimide component of the photopolymerizable compositions of the invention can be used singly or as mixtures thereof, and are useful as photopolymerizable initiators. The maleimide component can be present in the photopolymerizable composition in an amount sufficient to initiate polymerization thereof upon exposure to UV radiation. The composition can include about 0.01 to about 80 percent by weight. For pre-polymers and oligomers having both a maleimide component and a hydroxyalkylaminoalkylthioxanthone component, the maleimide concentration can be about 0.01 to about 20 percent by weight, or about 0.01 to about 10 percent by weight. [0027] The maleimide component can be an alkyl maleimide, functionalized aliphatic maleimide, aromatic maleimide, maleimide, maleic anhydride, or mixtures thereof. The maleimide component can be completely consumed during initiation and photopolymerization (i.e., incorporated into the polymer structure). For example, the maleimide component may be any of the maleimide compounds described in Hoyle, et al. (US Patent No. 6,555,593), which is hereby incorporated by reference in its entirety.

[0028] The photopolymerizable compositions of the present invention may also contain other conventional agents, such as polymerization inhibitors, fillers, ultraviolet absorbers, organic peroxides, dyes, pigments, and the like.

[0029] The photopolymerizable compositions can be applied or deposited on a surface of a substrate using conventional techniques and apparatus. The compositions can be applied as a substantially continuous film. Alternatively, the composition can be applied in a discontinuous pattern. The thickness of the deposited composition can vary, depending upon the desired thickness of the resultant cured product.

[0030] Typically, the substrate is coated with the uncured photopolymerizable composition and passed under a commercially available UV or exciter lamp on a conveyor moving at predetermined speeds. The substrate to be coated can be, for example, metal, wood, mineral, glass, paper, plastic, fabric, ceramic, and the like.

[0031] The active energy beams used in accordance with the present invention may be ultraviolet light or may contain in their spectra both visible and ultraviolet light. The polymerization may be activated by irradiating the composition with ultraviolet light using any of the techniques known in the art for ultraviolet radiation, i.e., in the range of 200nm and 450 nm, and especially with the 308 nm emission from xenon chloride exciter lamps. The radiation may be natural or artificial, monochromatic or polychromatic, incoherent or coherent and should be sufficiently intense to activate the photoinitiators of the invention and thus polymerization. Conventional radiation sources include fluorescent lamps, exciter lamps, mercury, metal additive and arc lamps. Coherent light sources include pulsed nitrogen, xenon, argon ion- and ionized neon lasers whose emissions fall within or overlap the UV absorption bands of the compounds of the invention.

[0032] The compositions are useful in any types of applications known in the art for photopolymerizations, including as a binder for solids to yield a cured product in the nature of a paint, varnish, enamel, lacquer, stain or ink. The compositions can also be useful in the production of photopolymerizable surface coatings in food packaging printing processes, such as lithographic printing, screen printing, and the like. The compositions can also be useful in applications in which the compositions are applied to articles that are to be exposed to the environment, such as signage.

[0033] The following examples illustrate the preparation of photopolymerizable compositions in accordance with the present invention.

Example 4:

Preparation of Pre-polymer:

[0034] A pre-polymer was prepared having NCO content of about 5 to about 7 wt% by reacting

TERATHANE 1000 [DuPont, poly (tetramethylene glycol), MW about 1000)] with isophorone diisocyanate following standard experimental procedures.

Preparation of Polyurethane-l (PU-I):

[0035] The pre-polymer (150 g) was charged to a jacketed glass reactor fitted with an axial flow overhead stirrer, dry-air bubbler, and a thermocouple. An antioxidant, 4-methoxyphenol (MEHQ, 0.05 g) was added, dried air was bubbled subsurface, and the temperature was adjusted to 42⁰C. Hydroxethylmaleimide (HEMI) (24 g) was charged at once to the reactor, which was then heated to 55-60°C for one hour. 2-[N-methyl-N-(2-hydroxyethyl)]ethylthioxanthone (MHAT) (8 g) was then dissolved in dry acetone (7.5 mL) and charged to the reactor. The reactor was stirred at 55-60°C for 30 minutes and then dibutyltindilaurate (0.07 g) was charged and the reactor was stirred at 60-65⁰C for 3 hrs. The NCO content of the reaction mixture was verified and then the polymer was end-capped by addition of ethanol (1 mL) and stirring the reaction mixture continued for another hour at 60-65°C. MEHQ (0.06 g) was added and stirred at 60-65⁰C for 30 minutes. The resulting oligomer's (PU-I) NCO content was zero, its viscosity was 8400 cP at 60°C, its maleimide content was 8.3 wt%, and its thioxanthone content of 2.6 wt%.

Preparation of Polyurethane-2 (PU-2):

[0036] The experimental procedure for PU-I was modified as follows: the amount of pre- polymer was reduced to 10Og; the amount of HEMI was reduced to 13 g; and the amount of MHAT was reduced to 13 g. The resulting oligomer had a viscosity of 8550 cP at 60°C, NCO content of zero, maleimide content of 6.4 wt%, and thioxanthone content of 6.3 wt%. [0037] The structure of both PU-I and PU-2 is illustrated by Structure (VII) below:

Preparation of Polyurethane-3 (PU-3):

[0038] The experimental procedure of PU-I was modified by substituting HEMI with 2- hydroxyehtylacrylate (19.8 g). The resulting oligomer had a viscosity of 3200 cP at 6O⁰C, NCO content of zero, acrylate content of 6.63 wt%, and thioxanthone content of 2.93 wt%. [0039] The structure of PU-3 is illustrated by Structure (VIII) below:

Preparation of C8-1000:

[0040] C8-1000 is a representative bis-maleimide oligomer that undergoes self-initiated photopolymerization under exposure to UV light prepared by end-capping pre-polymer with HEMI. This oligomer was used as a reference for comparing the performance of the photopolymerizable compositions of the present invention. The structure of C8-1000 is illustrated in Structure (IX);

Structure (DO

Results:

[0041] The prepared oligomers, PU-I, PU-2, and PU-3, were evaluated and compared to C8- 1000 in standard formulations with EBECRYL 3720 (UCB Chemicals Corporation) and trimethyolpropane ethoxytriacrylate (TMPEOTA). PU-3 exhibited more reactivity as compared to C 8- 1000 due to the presence of MHAT. PU-I and PU-2 exhibited even greater reactivity due to the combination of MHAT and HEMI end-caps.

Values expressed as wt%. [0042] In Figure 1, the photo-DSC exotherms illustrate the improved photopolymeric efficiency of MHAT as compared to isopropyl thioxanthone (ITX), a widely used conventional synergist.

[0043] Figure 2 illustrates the improved photopolymerization rate exhibited by a self-initiating oligomer end-capped with a hydroxyalkylaminoalkylthioxanthone of the present invention.

[0044] Further, standard formulations were compared employing PU-I and C8-1000, as well as non-oligomer bound MHAT and ITX to illustrate the effect on curing speed. The table below indicates a faster cure with MHAT and the greatest cure speed with oligomer bound MHAT (PU-I).

Values expressed as wt%.

[0045] While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions, methods and/or processes and in the steps or in the sequence of steps of the methods described herein without departing from the concept and scope of the invention. More specifically, it will be apparent that certain agents which are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the scope and concept of the invention.

Claims

CLAIMSWhat is claimed is:

1. A hydroxyalkylaminoalkylthioxanthone

wherein: each Ri is independently selected from the group consisting of hydrogen, halogen, Ci- Ci8 alkyl, C₃-C₆ cycloalkyl, and Ci-C₁₈ alkoxy;

R₂ is selected from the group consisting of C₂-Ci i alkyl;

R₃ is selected from the group consisting of hydrogen, Ci-Cg alkyl, Ci-C₈ cycloalkyl, Ci to Ci₂ alkoxy; and

R₄ is selected from the group consisting of Ci to Cu alkyl.

2. The hydroxyalkylaminoalkylthioxanthone of claim 1, wherein Ri is hydrogen; R₂ is selected from the group consisting OfC₂-Ci₁ alkyl; R₃ is selected from the group consisting of hydrogen, C₁-Cg alkyl, Ci-Cg cycloalkyl, Ci to Ci₂ alkoxy; and R₄ is selected from the group consisting of Cj to Ci ₁ alkyl.

3. The hydroxyalkylaminoalkylthioxanthone of claim 2, wherein R₂ is an ethyl group, R₃ is a hydroxyethyl group or a methyl group, and R₄ is an ethyl group.

4. The hydroxyalkylaminoalkylthioxanthone of claim 3, wherein R₂ is in the 2 or 4 position of the phenyl ring.

5. A hydroxyalkylaminoalkylthioxanthone

6. A hydroxyalkylaminoalkylthioxanthone

7. A vinylthioxanthone

wherein: each R] is independently selected from the group consisting of hydrogen, halogen, C₁-

C₁₈ alkyl, C₃-C₆ cycloalkyl, and C₁-Qg alkoxy; and Rs is selected from the group consisting of Ci-Cio alkyl.

8. The vinylthioxanthone of claim 7, wherein Rj is hydrogen and R₅ is a methyl group.

9. The vinylthioxanthone of claim 8, wherein R₅ is in the 2 or 4 position of the phenyl ring.

10. A vinylthioxanthone

11. A method of preparing the hydroxyalkylaminoalkylthioxanthone of claim 1 comprising the steps of: combining into a reaction mass, a bromoalkylthioxanthone, a hydroxyalkylamine, and a base, in a sufficient volume of a non-nucleophilic polar solvent to dissolve or disperse the solid reactants; heating the reaction mass to about the boiling point of the non-nucleophilic polar solvent; refluxing the reaction mass from about 1 to about 10 hours; and isolating the hydroxyalkylaminoalkylthioxanthone as a solid product.

12. The method of claim 11, wherein the base is an inorganic base.

13. The method of claim 12, wherein the base is selected from the group consisting of potassium carbonate, potassium bicarbonate, sodium carbonate, and sodium bicarbonate.

14. The method of claim 11, wherein the base is an organic base.

15. The method of claim 14, wherein the base is a tertiary amine.

16. The method of claim 11, wherein the solvent is acetonitrile.

17. The method of claim 11, wherein the bromoalkylthioxanthone is bromoethylthioxanthone, the hydroxyalkylamine is 2-(methylamino)ethanol, and the hydroxyalkylaminoalkylthioxanthone is 2-[N-methyl-N-(2-hydroxyethyl)] ethylthioxanthone.

18. The method of claim 11, wherein the bromoalkylthioxanthone is bromoethylthioxanthone, the hydroxyalkylamine is diethanolamine, and the hydroxyalkylaminoalkylthioxanthone is 2-[N,N-Bis(2-hydroxyethyl)]ethylthioxanthone.

19. A photopolymerizable composition comprising at least one photopolymerizable compound and a hydroxyalkylaminoalkylthioxanthone component, said hydroxyalkylaminoalkylthioxanthone component comprising at least one hydroxyalkylaminoalkylthioxanthone of claims 1-6.

20. The photopolymerizable composition of claim 19, wherein the at least one photopolymerizable compound is an acrylate, a methacrylate, a vinyl ether, or a mixture thereof.

21. The photopolymerizable composition of claim 19, wherein the concentration of the hydroxyalkylaminoalkylthioxanthone component in the photopolymerizable composition ranges between about 0.01 to about 20 weight percent.

22. The photopolymerizable composition of claim 19, further comprising a maleimide component.

23. The photopolymerizable composition of claim 22, wherein the concentration of the maleimide component in the photopolymerizable composition ranges between about 0.01 to about 80 weight percent.

24. The photopolymerizable composition of claim 23, wherein the concentration of the maleimide component in the photopolymerizable composition ranges between about 0.01 to about 20 weight percent.

25. A photopolymerizable composition comprising at least one photopolymerizable compound having a chemically bound hydroxyalkylaminoalkylthioxanthone component, said hydroxyalkylaminoalkylthioxanthone component derived from at least one hydroxyalkylaminoalkylthioxanthone of claims 1-6.

26. The photopolymerizable composition of claim 25, further comprising a maleimide component.

27. The photopolymerizable composition of claim 26, wherein the maleimide component is chemically bound to the at least one photopolymerizable compounds.

28. The photopolymerizable composition of claim 27, wherein the concentration of the maleimide component in the photopolymerizable composition ranges between about 0.01 to about 20 weight percent.

29. A method of photopolymerizing a photopolymerizable composition comprising exposing said photopolymerizable composition to radiation, wherein said photopolymerizable composition comprises a chemically bound hydroxyalkylaminoalkylthioxanthone component derived from at least one of the hydroxyalkylaminoalkylthioxanthones of claims 1 - 6.

30. The method of claim 29, wherein said photopolymerizable composition further comprises a maleimide component.