GB2100722A - Monomeric carbamic ester photoinitiators - Google Patents

Abstract

Actinic radiation curable monomers are prepared from the reaction of hydroxyalkyl acrylate or methacrylate esters, specific diisocyanate compounds and photoactivatable free radical polymerization initiators containing a single hydroxyl group of an alcoholic nature. They have the formula <IMAGE> in which PI in the initiator residue, B is phenylene, <IMAGE> or the residue of a di(NCO-terminated) prepolymer formed by reaction with a polyether, polyester or polyether-ester diol; R1 is H or C1-18 alkyl and R2 is H or CH3. The monomers are capable of undergoing rapid vinyl-type polymerization when exposed to actinic radiation and, alternatively, may be homo- or copolymerized with a wide variety of vinyl monomers using conventional polymerization techniques thereby producing copolymers which will rapidly crosslink when further exposed to actinic radiation.

Description

SPECIFICATION Monomeric photoinitiators This invention relates to actinic radiation curable monomers and the homo- and copolymers prepared therefrom. More particularly, the invention relates to a novel class of monomeric photoinitiators prepared from the reaction of hydroxyalkyl acrylate or methacrylate esters, specific diisocyanate compounds and photoactivatable free radical polymerization initiators containing a single hydroxyl group of an alcoholic nature. The monomers are capable of undergoing rapid vinyl-type polymerization when exposed to actinic radiation and have particular use in the preparation of photosensitive compositions. Alternatively, these monomers may be homo- or copolymerized with a wide variety of vinyl monomers using conventional polymerization techniques thereby producing copolymers which will rapidly crosslink when further exposed to actinic radiation.

It is well known that actinic curable compositions generally comprise a low molecular weight polyunsaturated resin dissolved in a selected combination of vinyl momomers to which a relatively small amount of a photoinitator is added. When the resultant mixture is coated on a substrate and cured by exposure to actinic radiation, a high molecular weight polymer is formed on the substrate.

It has been found desirable, for fast and efficient curing of such polymers, to include within the system relatively large amounts of the photoinitiating component. Such levels of photoinitiator cannot, however, be used with certain systems since these high levels of photoinitiator will not dissolve or mix homogeneously with the remainder of the system. Even in systems wherein these larger amounts of photoinitiators are compatible, most of the photoinitiator will remain chemically unbonded in the final cured composition producing deleterious effects on the properties of these cured materials. An additional drawback to the use of high levels of chemically unbonded photoinitiators is the possibility of the occurrence of side reactions on further exposure to actinic radiation.A further disadvantage of such post-added photoinitiators is the fact that even after curing the photoinitiators are not permanently bonded within the system and may leach out and cause undesirable contamination in the final polymerized composition. In systems which require synergists to effectively initiate polymerization, the presence of the necessary correspondingly high concentration of these synergistic chemicals would also result in a reduction in the desired properties of the cured compositions.

Various monomeric photoinitiators have been proposed wherein the photoinitating component becomes permanently incorporated into the backbone of the final cured polymer thereby avoiding many of the drawbacks discussed above. Many of these monomeric photoinitiators, however, are unduly sensitive to the effects of atmospheric oxygen and it is therefore necessary to polymerize such systems in an oxygen free environment. Still other monomeric photoinitiating systems are relatively slow to initiate polymerization upon exposure to actinic radiation and some even require the presence of additional synergistic components in order to cure satisfactorily.

The present invention provides a novel class of monomeric photoinitiators which are relatively insensitive to the effects of atmospheric oxygen and which will cure rapidly and efficiently when exposed to actinic radiation. It also provides high molecular weight copolyers with these photoinitiators, the presence of which renders the copolymers photosensitive and thus capable of undergoing rapid cross-linking when exposed to actinic radiation. It further provides such high molecular weight copolymer compositions which are capable of being employed in a wide range of forms, i.e. as solids, emulsion or aqueous latices.

The monomeric photoinitiators herein are characterized by the formula:

wherein PI is the photoreactive residue of a photoinitiating species containing a single hydroxyl group of an alcoholic nature; B is phenylene,

or the residue from a di(NCO-terminatedl prepolymer formed by reaction with a polyether, polyester or polyetherester diol; R, is hydrogen or an alkyl group containing 1-1 S carbon atoms and R2 is H or CH3 These compositions are capable of undergoing rapid vinyl-type polymerization of either a homopolymeric or copolymeric nature with little or no inhibition from atmospheric oxygen when exposed to a source of actinic radiation.

These monomeric photoinitiators may be prepared by the reaction of approximately equimolar amounts of the respective components, i.e. the photoinitiating species, the diisocyanate and the hydroxy-acrylate or hydroxy-methacrylate ester. The resulting monomeric photointiators may be used alone or in combination with a variety of copolymerizable monomers and when subjected to actinic radiation will cure or polymerize to form a smooth, non-tacky or a soft, tacky surface depending upon the particular components and amounts used. Alternatively, the novel monomers may be homo- or copolymerized using conventional polymerization techniques to produce a high molecular weight copolymer containing the photoinitiating component.The resultant copolymers may be used in solid form or as emulsions or solutions and will exhibit rapid cross-linking when exposed to a source of actinic radiation thereby imparting desirable properties to the final polymerized composition.

In either case, the addition of these photoinitiating monomers as permanently bonded portions of the resulting compositions not only obviates the difficulties inherent in the use of extraneously added photoinitiators, such as migration and nonuniformity, but also increases the polymerizing efficiency of the polymer to a degree which was not previously attainable by the use of post-added initiators.

The photoinitiating species employed herein are those conventional photoactivatable free radical polymerization initiators containing a single hydroxyl group of an alcoholic nature. In particular we have found photoinitiators of the following three specific classes to be useful herein:

where Z1 and Z2 are independently-H, -CH3, -OR, or --CO,R; R is H, or C1 to C4 alkyl and X is chlorine or bromine; m is an integer 0 to 5; and n is an integer 1-5. Particularly preferred photoinitiating species are ,B-hydroxypropyl ester of o-benzoylbenzoic acid, benzoin, and 2pentachlorophenoxy ethanol.

Suitable hydroxyalkyl acrylate and methacrylate esters for use herein will have 2 to 20 carbon atoms in the alkyl group, e.g. hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxypentyl acrylate, etc. as well as the corresponding methacrylates and combinations thereof.

The diisocyanates which are used in the present reaction are those wherein the isocyanate substituents possess a differential degree of reactivity. Particularly useful isocyanates include methylene bis-phenylene diisocyanate, isophorone diisocyanate, 2,4-toluene diisocyanate, as well as mixtures thereof. Also useful herein are isocyanate terminated prepolymers derived from the reaction of the diisocyanates with conventional polyether, polyester or polyether ester diols. Representative prepolymers are those prepared from reaction of the diisocyanate components with such diols as polyethylene diol, polypropylene diol, 1,3-triethylene diol, 1,4-butyleneadipate diol, diethyleneglycoladipate diol, and mixtures thereof.

The proportions of the reactants employed in producing the monomeric photoinitiators is not critical; however, to obtain maximum conversion with maximum purity, equimolar portions of each are preferred. It will be understood by those skilled in the art that, depending upon the reaction efficiency of the individual components, it may be desirable to employ any of the reactants in an amount of up to about 20% in excess of the stoichiometric amount in order to obtain a more fully converted monomeric species.

In general, it is preferred that reaction be carried out in two stages. In the first stage the diisocyanate is reacted with the component containing the least reactive hydroxyl substituent. This reaction is usually carried out (sometimes in the presence of a small amount of solvent) at temperatures of 20-800C for periods of 1 to 8 hours and usually requires no catalyst. The second stage, involving the resultant isocyanate-containing reaction product and the remaining component, is carried out at temperatures of 40-1 000C for 1 to 8 hours using 0.001 to 1.0% of catalysts known for their ability to catalyze the reaction with isocyanates.In particular certain tin compounds have been found to be useful, e.g. di-n-butyltin oxide, tri-n-butyitin acetate, n-butyltin trichloride, trimethyltin hydroxide, dimethyltin dichloride, stannous octanoate, di-n-butyltin dilaurate. It is a matter of ordinary preparative experience on the part of the practitioner to determine the precise combinaton of time and temperature which will be best suited for the synthesis of the specific monomeric photoinitiator. If the diisocyanate terminated prepolymers are used herein, the prepolymer may be added directly as described above or may be formed in situ by first reacting the photoinitiating species with the diisocyanate and then adding the particular polyurethane or polyester diol.Additional isocyanate may be added in proportions to achieve the molecular weight range desired and to retain the residual isocyanate functionality required to enter into subsequent reaction with the hydroxyl monomers. The reaction is terminated when conversion of the reactant is found to be substantially complete as may be determined, for example, by titration, where applicable, of an aliquot that has indicated a zero or near zero value of residual isocyanate.

Upon completion of the reaction and subsequent cooling of the reaction vessel to room temperature, the resulting products will usually be in the form of either crystalline solids or viscous oils.

For most purposes, including any subsequent photoinitiated polymerization reactions, this crude monomer can be used without further purification. However, when desired, the relatively small amount of unreacted starting materials may be removed. Thus, such means as chromatographic separation techniques as, for example, the use of a silica gel column, have been found to yield a product which, by means of saponification equivalent analysis, will indicate a purity of almost 1009/0, by weight. Other separation techniques, such as aqueous alkali or organic solvent extraction procedures, may also be used.

Additionally, it is possible to prepare the novel photoinitiating monomers herein by reaction in an organic solvent medium. Under these conditions, the individual components may all be dissolved in a non-reactive polar solvent such as acetone, methyl ethyl ketone, tetrahydrofuran, dimethylformamide or dimethylsulfoxide. The resulting product is recovered by removing the solvent whereupon the crude product may, if desired, be purified by means of the above noted techniques. The use of such solvents are not preferred, however, since the reaction rate is substantially reduced.

If desired, conventional non-manomeric functional additives may be incorporated into the monomeric compositions resulting from the above described reaction in order to modify the properties thereof. Among the additives which may be included are fillers such as finely ground resins; polymerization inhibitors such as p-methoxyphenol and the like; pigments such as titanium dioxide, barium sulfate, calcium carbonate, and the like; ultraviolet light transparent dyes such as Brilliant Violet B, Fast Red 8BLX; plasticizers, etc.

In addition to the monomeric products as well as the non-monomeric functional additives described above, the photoinitiating compositions herein may also optionally include up to about 99%, preferably up to about 50%, by weight of mers derived from at least one copolymerizable diluent comonomer. Suitable ethylenicaily unsaturated comonomers include (i) acrylic and methacrylic acids;; (ii) the alkyl and substituted alkyl esters of said acids wherein the alkyl groups contain from 1 to 20, preferably 2 to 12, carbon atoms, e.t. ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, 2-ethyi hexyl acrylate, dodecyl acrylate, etc., (iii) the hydroxyalkyl esters of said acids, wherein the alkyl group contains from 2 to 20, preferably 2 to 6, carbon atoms, e.g. 2-hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxypentyl acrylate, hydroxyhexyl acrylate, hydroxyheptyl acrylate, hydroxyoctyl acrylate, etc. and the corresponding hydroxyalkyl methacrylates; (iv) the cycloalkyl ester derivatives of said acids wherein the cycloalkyl groups contain from 5 to 10 carbon atoms, e.g. cyclohexyl acrylate or cyclohexyl methacrylate; (v) the glycidyl esters of said acids; (vi) the ethylene glycol and polyethylene glycol diesters of said acids, e.g. ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, etc. and the corresponding ethylene glycol dimethacrylates and polyethylene glycol methacrylates; (vii) the polyhydric alcohol ester derivatives of said acids, e.g. the pentaerythritol tri- and tetraacrylates and the corresponding methacrylates; and (viii) the alkanediol (C28) ester derivatives of said acids, e.g. 1,6hexanediol diacrylate.

The novel monomeric photoinitiators may be employed at the temperatures at which they are prepared or at ambient temperatures and may be applied to the substrate by means of any conventional coating technique in order to produce the desired overcoating, protective coating, printing or decorative coating or the like. Thus, the novel photocurable coating compositions may be applied by use of any mechanical coating process such as air knife, trailing blade, knife coater, reverse roll or gravure coating techniques. Since the adaptability of a suitable method of coating will depend to some extent on the shape or form of the substrate, selection of a particular technique is left to the practitioner.

It may also be desirable to adjust the viscosity of a stored composition in order to facilitate coating. The particular method selected for this purpose and the feasibility thereof will depend considerably on the rheological properties of the composition. Similarly, the coating weights will depend on the particular method of application and the specific end use desired.

The photocurable monomers may be coated onto virtually unlimited variety of substrates, including paper, cloth, paperboard, metal sheets and foils, glass, fiberglass, foamed plastic, rubber, cellophane, wood and plastic films and sheets, such as those derived from polyethylene terephthalåte, polystyrene, rubber hydrochloride, polyvinyl chloride, polyvinylidene chloride, and any substrate where there is sufficient adhesion to the coated film. Moreover, these novel active radiation curable monomers may be used as adhesives to laminate two substrates where at least one substrate can be penetrated by actinic radiation.

Subsequent to application, regardless of the ultimate intended use, the monomeric composition in its applied form, eg. as a film is polymerized (cured) upon exposure to actinic radiation having a wavelength of 2000 to 5000 A, for a period of time sufficient to accomplish the desired amount of polymerization. Ordinarily, a period of one-half second or less at a wavelength of 2500 to 4000 A is sufficient to insure adequate curing of most films and coatings.

This polymerization or curing may be conducted while the monomeric material is still in the initial physical form resulting from its preparation. However, it is preferred and more convenient to effect the curing after the composition has been formed into a shaped article, e.g. a film, coating or molded structure. This latter sequence of steps is particularly preferred when the coating is intended for a nonadhesive use, e.g. overcoating or protective coating, etc. It is also to be noted that since these uncured photocurable coating compositions display appreciable tack and cohesive characteristics, it is preferred that a removal cover sheet be utilized whenever it is elected to delay curing for a considerable period.

As an alternate embodiment herein, instead of subjecting the monomeric photoinitiator to curing (polymerizing) by exposure to actinic radiation, the monomer may be homo- or copolymerized using any of the known vinyl polymerization methods. The resulting homo- or copolymers prepared by this embodiment thereby contain the photoinitiating monomer in a permanently bound form and, when the polymer is then exposed to actinic radiation, the self-contained photoinitiating component will effect curing by crosslinking throughout the polymer thereby enhancing the properties thereof.

The vinyl monomers and vinyl monomer combinations which may be used in preparing the copolymers of this embodiment may be chosen from a virtually unlimited variety of copolymerizable ethylenically unsaturated monomers. Representative monomers include (i) acrylic and methacrylic acids; (ii) the alkyl and substituted alkyl esters of said acids wherein the alkyl groups contain from 1 to 20, preferably 2 to 12, carbon atoms, e.g. ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, stearyl acrylate, etc. and the corresponding methacrylates; (iii) the hydroxyalkyl esters of said acids wherein the alkyl group contains from 2 to 20, preferably 2 to 6 carbon atoms, e.g. 2hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxypentyl acrylate, hydroxyhexyl acrylate, etc. and the corresponding methylates; (iv) the cycloalkyl (Cs~1o) ester derivatives of said acids, e.g. cyclohexyl acrylate and cyclohexyl methacrylate; (v) the glycidyl esters of said acids; (vi) vinyl acetate; (vii) styrene; (viii) other ethylenically unsaturated monomers, e.g. N,N,N trimethyl-N-(3-methacryloxy-2-hydroxy propyl) ammonium methylsulphate, dimethylaminoethyl methacrylate and sodium vinyl sulfonate. Any of these monomers may be used either alone or in combination with one another together with one or more of the monomeric photoinitiators herein.

These polymers may be prepared by means of any conventional free radical initiated processes utilizing bulk, suspension, solution or emulsion polymerization techniques; or, they may be prepared by ionic catalysis or by means of stereospecific catalysts such as those of the type developed by Ziegler. In order to effectively crosslink the resultant polymer upon exposure to actinic radiation, the copolymers of this particular embodiment should contain at least 0.1%, preferably 1.0-1 5%, by weight, of mers derived from at least one of the monomeric photoinitiators.

In addition to their sensitivity to actinic radiation, the unique copolymers of this embodiment have the further advantage of being readily soluble in inorganic or organic solvents prior to irradiation and may therefore be employed in a variety of forms, e.g. as solids, solution polymers or aqueous latices.

Moreover, the ability of these copolymeric photoinitiators to further polymerize with virtually any ethylenically unsaturated comonomeric material permits the production of a final photocurable (crosslinking) composition which may be prepared so as to obtain the benefit of any of a wide range of polymeric backbone compositions.

In addition to the preparation of conventional randon copolymers, it is also possible to prepare graft copolymers wherein the monomeric photoinitiator herein is polymerized in the presence of previously prepared vinyl polymers such as polyolefins, polyvinyl halides and polyvinyl esters. The resulting graft copolymers also exhibit excellent crosslinking properties upon being exposed to actinic radiation.

The copolymers or graft copolymers described in this embodiment may be used alone or in combination with any of the monomeric diluents previously described and may be applied to substrates and cured in the same manner as the photoinitiating monomers contained therein. The resulting cured substrate is characterized by a smooth, hard non-tacky or soft, tacky appearance depending upon the specific components and amounts employed.

In the following examples, all quantities are given in terms of grams unless otherwise specified.

Example I This example relates to the preparation of a monomeric photoinitiator in accordance with the present invention.

A one-liter flask equipped with a heating and stirring means, a condenser, thermometer and slowaddition funnel was charged with 1 74 g. toluene diisocyanate and 212 g. benzoin. The mixture was heated with stirring to 650C. until an NCO titration indicated about 2.6 milliequivalents of free NCO/g.

of sample. At this point, 0.3 g. dibutylin dilaurate was added followed by the addition of 143 g. (10% excess) 2-hydroxypropyl acrylate over a 2 hour period. After heating for one hour, samples were periodically taken for NCO analysis. Heating was continued until analyses indicated about 0.1 me/g. or less free NCO. The flask was emptied and the product solidified on cooling to form a crystalline mass.

Examples li-Ill The procedure described in Example I was repeated using 212 parts benzoin, 1 74 parts toluene diisocyanate and 128 parts hydroxyethyl acrylate. Upon cooling, a crystalline product was formed.

The procedure was again repeated using 284 parts 2-hydroxypropyl o-benzoylbenzoate, 222 parts isophorone diisocyanate and 143 parts hydroxypropyl acrylate to form a reaction product which was a viscous oil.

Example IV This example illustrates the preparation of a monomeric photo-initiator according to the present invention using a di(NCO-terminated) prepolymer formed in situ.

A reaction vessel similar to that used in Example I was charged with 63.6 g. benzoin, 10 g. 2pentanone, and 52.2 g. toluene diisocyanate. Heating was started and the exothermic nature of the reaction carried the internal temperature up to about 1000C. After the exotherm was completed, the reaction was maintained at 850C. until an analysis for NCO groups indicated a value of about 2.4 me/g.

The temperature was lowered to 75-800C. and 0.25 g. dibutylin dilaurate was added. Then 120 g.

polyethylene glycol was slowly added with heating continued until an NCO analysis indicated a value of less than 0.1 me/g. Additional 52.2 g. toluene diisocyate was addded and the heating continued until analysis indicated essentially complete removal of one isocyanate group. At this point 34.8 g.

hydroxyethyl acrylate was added and the reaction continued until residual isocyanate groups mounted to less than 0.1 me/g. A polymerization inhibitor (0.1% p-methoxyphenol) was then added and the reaction mixture was cooled yielding a clear, highly viscous monomeric product.

Example Using the procedure described in Example IV, other polyether and polyester diols were employed to form the di(NCO-terminated)prepolymer in situ. The particular diols and the amounts used are shown in Table Table I

Diol Amount (gel 1,3-Triethylene 45 Polypropylene 569 Polypropylene 128 Polypropylene 878 Polypropylene 295 Polypropylene 1260 1,4-butanedioladipate 340 Diethyleneglycoladipate 324 Diethyleneglycoladipate 915 Diethylenoglycoladipate 1224 Polypropylene 199 mixture Polypropylene 199 mixture Polypropylene 398 Diethyleneglycoladipate 104 Example VI A sample of the product from Example IV was spread on a glass slide and exposed to the ultraviolet light emitted by a 250 watt GE RS sunlamp at a distance of 12 inches. In less than 60 seconds, the resin had solidified to a strong flexible film. The surface of the polymer gave no indication of unpolymerized product, indicating little or no effect by atmospheric oxygen.

Example VII A sample of the product from Example I was mixed with an equal weight of hydroxyethyl acrylate.

Upon irradation to U.V. as above, the fluid mass was converted to a rubbery cross-linked polymer in about 10 seconds. No surface tackiness was observed.

Example VIII A sample of the product from Example IV was copolymerized with an equal amount of vinyl acetate in ethyl acetate solvent. A portion of this dried polymer was then mixed until homogeneous with methyl acrylate in a 2 to 1 ratio. Upon irradiation, polymerization of the methyl acrylate ensued.

The resultant product appeared to be a graft copolymer of polymethyl acrylate.

Summarizing, monomeric photoinitiators prepared from the reaction of hydroxyalkyl acrylate or methacrylate esters, specific diisocyanate compounds, and photoactivatable free radical polymerization initiators containing a single hydroxy group of an alcoholic nature are provided, as well as their mixtures with other monomer(s) and the cured polymers thereof.

Claims (12)

Claims

1. A monomeric photoinitiator of the formula:

wherein PI is the residue of a photoinitiating species containing a single hydroxy group of an alcoholic nature; B is phenylene,

or the residue of a di(NC0-terminated) prepolymer formed by reaction with a polyether, polyester or polyether-ester diol; R1 is hydrogen or an alkyl group containing 1-1 8 carbon atoms and R2 is H or CH3.

2. A photoinitiator according to claim 1, wherein Pl is the residue of a photoinitiator species of the formula:

where Z1 and Z2 are independently -H, CH3, -OR, or --CO,R; R is H, or C, to C4 alkyl; X is chlorine or bromine; m is an integer 0--5 and n is an integer 1-5.

3. A photoinitiator according to claim 1, wherein Pl is the residue of benzoin, p- hydroxypropylester of o-benzoylbenzoic acid, or 2-hydroxyethoxy-(pentachlorophenol).

4. A photoinitiator according to claim 1,2 or 3 wherein R1 is hydrogen, methyl, or ethyl and B is the residue of a di-(NC0-terminated) species selected from methylene bis-phenylene diisocyanate, isophorone diisocyanate, 2,4-toluene diisocyanate, and di(NCO-terminated) prepolymers, formed from the reaction of methylene bisphenylene diisocyanate, isophorone diisocyanate, or 2,4-toluene diisocyanate with a diol selected from polyethylene diol, 1 ,3-triethylene diol, polypropylene diol, 1,4- butyleneadipate diol, diethyleneglycoladipate diol and mixtures thereof.

5. A photoinitiator according to claim 1 substantially as described in any one of Examples I to IV.

6. A process for the production of a monomeric photoinitiator of the formula:

wherein PI is the residue of a photoinitiator species containing a single hydroxy group of an alcoholic nature; B is phenylene,

or the residue of a di-(NCO terminated) prepolymer formed by reaction with a polyether, polyester or polyether-ester diol;R, is hydrogen or an alkyl group containing 1-18 carbon atoms and R2 is H or CH3, which comprises reacting approximately equimolar amounts of: a) a photoinitiator species selected from

where Z, and Z2 are independently -H, -CH3, -OR, or -CO2R; R is H, or C, to C4 alkyl; and X is chlorine or bromine; m is an integer 0--5; and n is an integer 1-5; b) a diisocyanate selected from methylene bis-phenylene diisocyanate, isophorone diisocyanate, 2,4-toluene diisocyanate, or a prepolymer derived from the reaction of a diisocyanate with a polyether, polyester or polyetherester diol; and c) a hydroxyalkyl acrylate or methacrylate ester containing 2 to 20 carbon atoms in the alkyl residue.

7. A monomeric photoinitiator when produced by the process claimed in claim 6.

8. An actinic radiation curable composition comprising a mixture of monomeric photinitiator as claimed in any one of claims 1 to 5 or 7 and at least one ethylenically unsaturated monomer selected from (i) acrylic and methacrylic acids; (ii) the alkyl and substituted alkyl (C1~20) esters of acrylic or methacrylic acids; (iii) the hydroxyalkyl (C220) esters of acrylic or methacrylic acids; (iv) the cycloalkyl (Cs~1o) ester derivatives of acrylic or methacrylic acids (v) the glycidyl esters of acrylic or methacrylic acids; (vi) the ethylene glycol and polyethylene glycol diesters of acrylic or methacrylic acids; (vii) the polyhydric alcohol ester derivatives of acrylic or methacrylic acids; and (viii) the alkanediol (C28) ester derivatives of acrylic or methacrylic acids.

9. An actinic radiation curable composition comprising the free-radical addition polymerization product of a monomeric photoinitiator as claimed in any one of claims 1 to 5 or 7 and at least one ethylenically unsaturated monomer selected from (i) acrylic or methacrylic acid; (ii) hydroxyalkyl (C220) esters of acrylic or methacrylic acid; (iii) glycidyl esters of acrylic or methacrylic acid; (iv) cycloalkyl (C5~tO) esters of acrylic or methacrylic acid; (v) alkyl and substituted alkyl (C,~20) esters of acrylic or methacrylic acid; (vi) vinyl acetate; (vii) styrene, (viii) N,N,N-trimethyl-N-(3-methacryloxy-2hydroxypropyl)-ammonium methylsulphate, dimethylaminoethyl methacrylate and sodium vinyl sulfonate.

10. A composition as claimed in claim 8 or 9, wherein the ethylenically unsaturated monomer is hydroxyalkyl (C220) ester of acrylic or methacrylic acid.

11. A cured composition of matter prepared by exposing a composition as claimed in any of claims 1 to 5 or 7 to 9 to actinic radiation of wavelength in the range of 2000 to 5000 .

12. A coated article comprising a substrate coated with a composition of claim 8, 9 or 10 which has been cured.