METHOD OF PREPARING A MONOMERIC PHOTOINITIATOR

Abstract

Methods of preparing a monomeric photoinitiator comprising preparing a compound having an ethylenically unsaturated group and a moiety that is decomposable under photo-irradiation to form a radical useful in preparing a copolymer having pendant photoreactive groups; methods of making the radical and the resulting copolymer.

Claims

1. A method of preparing a compound of Formula (V): ##STR00022## wherein: R.sup.6 to R.sup.9 are independently selected from H, C.sub.1-C.sub.6 alkyl, C.sub.1-C.sub.6 alkoxy, C.sub.1-C.sub.12 alkoxyalkyl, SR.sup.12, COOR.sup.12 and N(R.sup.12).sub.2; wherein each R.sup.12 is independently selected from C.sub.1-C.sub.6 alkyl or C.sub.6-C.sub.18 aryl, subject to the proviso that n of radicals R.sup.6 to R.sup.9 are R.sup.bOC(O)C(R.sup.13)CH.sub.2; and R.sup.13 is H or C.sub.1 alkyl; n is an integer of from 1 to 3; and, for each of said n radicals, R.sup.b is independently selected from a covalent bond, C.sub.2-C.sub.12 alkylene, C.sub.3-C.sub.18 cycloalkylene or C.sub.6-C.sub.18 arylene, said method comprising steps of: i) reacting a disulfide compound of Formula (I) with a hydroxyl functional compound of Formula (II) to yield a compound of Formula (III) ##STR00023## wherein: said reaction is performed in an acidic medium having a pH at or below 4.0; R.sup.2 to R.sup.5 are independently selected from H or C.sub.1-C.sub.6 alkyl; R.sup.6 to R.sup.9 correspond to said substituents R.sup.6 to R.sup.9 and are independently selected from H, C.sub.1-C.sub.6 alkyl, C.sub.1-C.sub.6 alkoxy, C.sub.1-C.sub.12 alkoxyalkyl, SR.sup.12, COOR.sup.12 and N(R.sup.12).sub.2; each R.sup.12 is independently selected from C.sub.1-C.sub.6 alkyl or C.sub.6-C.sub.18 aryl, subject to the proviso that n of radicals R.sup.6 to R.sup.9 are R.sup.b(OH) wherein, for each of said n radicals, R.sup.b is independently selected from a covalent bond, C.sub.2-C.sub.12 alkylene, C.sub.3-C.sub.18 cycloalkylene or C.sub.6-C.sub.18 arylene; and R.sup.10 and R.sup.11 are H; and ii) reacting in an inert aprotic solvent said compound of Formula (III) with a compound of Formula (IV) to yield said compound of Formula (V) ##STR00024## wherein: X is halide or OC(O)C(R.sup.13)CH.sub.2; and, the number of moles of (meth)acrylate groups provided by said compound of Formula (IV) is at least equimolar with the number of moles of hydroxyl groups provided by the compound of Formula (III).

2. The method according to claim 1, wherein R.sup.2 to R.sup.5 are independently selected from H or C.sub.1-C.sub.4 alkyl.

3. The method according to claim 2, wherein R.sup.2 to R.sup.5 are independently selected from H or C.sub.1-C.sub.2 alkyl.

4. The method according to claim 3, wherein R.sup.2 to R.sup.5 are each H.

5. The method according to claim 4, wherein in Formula (II): R.sup.6 to R.sup.9 are independently selected from H, C.sub.1-C.sub.4 alkyl, C.sub.1-C.sub.4 alkoxy, C.sub.1-C.sub.8 alkoxyalkyl, COOR.sup.12 and N(R.sup.12).sub.2; each R.sup.12 is independently selected from C.sub.1-C.sub.4 alkyl or C.sub.6-C.sub.18 aryl, subject to the proviso that n of radicals R.sup.6 to R.sup.9 are OH, wherein n is an integer of 1 or 2; and R.sup.10 and R.sup.11 are H.

6. The method according to claim 5, wherein said acidic medium of step i) has a pH at or below 3.5.

7. The method according to claim 6, wherein step i) is performed at a temperature below the boiling point of the acid medium.

8. The method according to claim 1, wherein step i) is performed at a temperature of from 20 C. to 120 C.

9. The method according to claim 8, wherein in step ii) the molar ratio of (meth)acrylate groups provided by said compound of Formula (IV) to hydroxyl groups provided by said compound of Formula (III) is from 1:1 to 2:1.

10. The method according to claim 9, wherein X is halide.

11. The method according to claim 10, wherein the reaction of step ii) is performed in the presence of a base.

12. The method according to claim 11, wherein said base is selected from the group consisting of: tri(C.sub.1-C.sub.12)alkyl amines; di(C.sub.1-C.sub.12)alkyl(C.sub.3-C.sub.5) cycloalkyl amines; tri(C.sub.1-C.sub.10)alkenyl amines; and, mixtures thereof.

13. The method according to claim 11, wherein said base is selected from the group consisting of: trimethylamine; ethyldimethylamine; diethylmethylamine; triethylamine; triisopropylamine; tri-n-propylamine; tri-n-butylamine; tri-sec-butylamine; dibutylpentylamine; n-butyl-octyl-sec-butylamine; tripentylamine; trihexylamine; and, mixtures thereof.

14. The method according to claim 1, wherein step i) is performed at a temperature of 40 to 120 C.; step ii) is performed at a temperature of from 40 to 20 C.

15. The method according to claim 8 wherein step i) is performed at a temperature of from 60 to 100 C.; step ii) is performed at a temperature of from 20 to 20 C.

16. The method according to claim 1 of preparing a compound of Formula (VA): ##STR00025## wherein: R.sup.6 to R.sup.9 are independently selected from H, C.sub.1-C.sub.4 alkyl, C.sub.1-C.sub.4 alkoxy, C.sub.1-C.sub.8 alkoxyalkyl, COOR.sup.12 and N(R.sup.12).sub.2; and, each R.sup.12 is independently selected from C.sub.1-C.sub.4 alkyl or C.sub.6-C.sub.18 aryl, subject to the proviso that n of radicals R.sup.6 to R.sup.9 are OC(O)C(R.sup.13)CH.sub.2, wherein R.sup.13 is H or C.sub.1 alkyl and further wherein n is an integer of 1 or 2, said method comprising the steps of: i) reacting a disulfide compound of Formula (IA) with a hydroxyl functional compound of Formula (II) to yield a compound of Formula (IIIA) ##STR00026## wherein: said reaction is performed in an acidic medium having a pH at or below 3.0; said reaction is performed at a temperature below the boiling point of the acidic medium and in the range from 40 to 120 C.; R.sup.6 to R.sup.9 correspond to said substituents R.sup.6 to R.sup.9 and are independently selected from the H, C.sub.1-C.sub.4 alkyl, C.sub.1-C.sub.4 alkoxy, C.sub.1-C.sub.8 alkoxyalkyl, COOR.sup.12 and N(R.sup.12).sub.2: each R.sup.12 is independently selected from C.sub.1-C.sub.4 alkyl or C.sub.6-C.sub.18 aryl, subject to the proviso that n of radicals R.sup.6 to R.sup.9 are OH, wherein n is an integer of 1 or 2; and R.sup.10 and R.sup.11 are H; ii) reacting in an inert aprotic solvent said compound of Formula (IIIA) with a compound of Formula (IV) to yield said compound of Formula (VA) ##STR00027## wherein: X is chloride; the molar ratio of (meth)acrylate groups provided by said compound of Formula (IV) to hydroxyl groups provided by said compound of Formula (IIIA) is from 1.1:1 to 1.5:1; and, the reaction of step ii) is performed in the presence of a base selected from the group consisting of: tri(C.sub.1-C.sub.12)alkyl amines; di(C.sub.1-C.sub.12)alkyl(C.sub.3-C.sub.8) cycloalkyl amines; tri(C.sub.1-C.sub.10)alkenyl amines; and, mixtures thereof.

17. A method of making a copolymer comprising a free-radical polymerization of a monomer compound of Formula (V) obtained in accordance with the method of claim 1.

18. A copolymer obtained by free radical polymerization, said copolymer comprising, based on the total weight of monomers: from 0.1 to 10 wt. % of a) at least one compound of Formula (V) obtained in accordance with the method of claim 1; and, from 90 to 99.9 wt. % of b) at least one ethylenically unsaturated non-ionic monomer which does not bear an epoxide group or a moiety decomposable under photo-irradiation to form a radical.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0078] FIG. 1 shows the two-step reaction sequence of the method of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0079] The two steps of the method of the present disclosure are illustrated in FIG. 1 appended hereto.

Step i)

[0080] The first stage of the present disclosure includes the provision, as a reactant of a disulfide compound in accordance with Formula (I) herein below:

##STR00006## [0081] wherein: R.sup.2 to R.sup.5 are independently selected from H or C.sub.1-C.sub.6 alkyl.

[0082] It is preferable that R.sup.2 to R.sup.5 be independently selected from H or C.sub.1-C.sub.4 alkyl and more preferable that R.sup.2 to R.sup.5 be independently selected from H or C.sub.1-C.sub.2 alkyl. In an important embodiment, R.sup.2 to R.sup.5 are each H, whereby the reactant in accordance with Formula (I) is 2,2-dithiodibenzoic acid.

[0083] The first stage of the present disclosure also encompasses the provision of a hydroxyl functional reactant in accordance with Formula (II) herein below:

##STR00007## [0084] wherein: R.sup.6 to R.sup.9 are independently selected from H, C.sub.1-C.sub.6 alkyl, C.sub.1-C.sub.6 alkoxy, C.sub.1-C.sub.12 alkoxyalkyl, SR.sup.12, COOR.sup.12 and N(R.sup.12).sub.2; [0085] R.sup.10 and R.sup.11 are H; and, [0086] each R.sup.12 is independently selected from C.sub.1-C.sub.6 alkyl or C.sub.6-C.sub.18 aryl, [0087] subject to the proviso that n of radicals R.sup.6 to R.sup.9 are R.sup.b(OH), wherein n is an integer of from 1 to 3 and for each of said n radicals R.sup.b is independently selected from a covalent bond, C.sub.2-C.sub.12 alkylene, C.sub.3-C.sub.18 cycloalkylene or C.sub.6-C.sub.18 arylene.

[0088] As regards Formula (II), it is preferred that: [0089] R.sup.6 to R.sup.9 are independently selected from the H, C.sub.1-C.sub.4 alkyl, C.sub.1-C.sub.4 alkoxy, C.sub.1-C.sub.8alkoxyalkyl, COOR.sup.12 and N(R.sup.12).sub.2; [0090] R.sup.10 and R.sup.11 are H; and, [0091] each R.sup.12 is independently selected from C.sub.1-C.sub.4 alkyl or C.sub.6-C.sub.18 aryl, [0092] subject to the proviso that n of radicals R.sup.6 to R.sup.9 are R.sup.bOH, wherein n is an integer of 1 or 2.

[0093] In this first stage (i)), the disulfide compound of Formula (I) is reacted with the hydroxyl functional compound of Formula (II) to yield a hydroxyl functional compound in accordance with Formula (III).

##STR00008##

[0094] For completeness, within the compound of Formula (III) depicted above and in FIG. 1, substituents R.sup.2 to R.sup.9 have the meanings accorded above.

[0095] The reaction of this step is performed in an acidic medium having a pH at or below 4.0. The acidic medium may, in certain embodiments, have a pH at or below 3.5 or at or below 3.0. Illustrative acidic media which may be used include: concentrated sulphuric acid; concentrated mixtures of sulphuric acid and acetic acid; concentrated hydrochloric acid; concentrated phosphoric acid (H.sub.3PO.sub.4); acetic acid; and, mixtures of acetic acid and acetic anhydride. In forming the acidic reaction medium, the number of moles of acid should typically be at least ten times that of the reactant compound (I).

[0096] The reaction temperature should be below the boiling point of the acidic medium and is typically selected to be in the range from 20 C. to 120 C., for example from 40 to 120 C. or from 60 to 100 C. In certain embodiments, the reaction may be performed under a multi-stage regime with respect to temperature. For instance, the reactants and acid of the medium may be initially mixed at room temperature and the temperature of the mixture-under continual stirring-then slowly elevated to a range of from 40 to 120 C. for a first duration, for instance of from 1 to 5 hours. Under maintained stirring, the temperature of the mixture may then be allowed to return to room temperature and the reaction permitted to continue for a second duration, for instance from 2 to 12 hours.

[0097] Subject to the proviso that the acidic medium should not be boiling, the process pressure is not critical: as such, the reaction can be run at sub-atmospheric, atmospheric, or super-atmospheric pressures but pressures at or slightly above atmospheric pressure are preferred. Mention in this regard may be made of pressures of from 50 to 200 kPa, for example from 100 to 200 kPa.

[0098] The progress of the above reaction step i) may be monitored by known techniques of which mention may be made of 1H NMR, Fourier Transform Infrared Spectroscopy, Ultra Performance Liquid Chromatography (UPLC) or thin layer chromatography (TLC). Upon completion of the reaction, the compound of Formula (III) is precipitated from the product mixture, typically by introducing that mixture into boiling water. The precipitate may then be separated and washed, typically with water.

[0099] The crude solid product obtained may subsequently be purified by methods known in the art, including but not limited to solvent extraction, filtration, evaporation, distillation, (re-)crystallization and chromatography. Mention may in particular be made of the re-crystallization of the product from a C.sub.1-C.sub.4 alkanol, such as methanol.

Step ii)

[0100] In this step, the compound of Formula (III) is reacted, in an inert aprotic solvent, with a (meth)acrylating agent selected from the group consisting of (meth)acryloyl halides and (meth)acrylic anhydrides. More particularly, said methacrylating agent has the Formula (IV) below:

##STR00009## [0101] wherein: X is halide or OC(O)C(R.sup.13)CH.sub.2; and, [0102] R.sup.13 is H or C.sub.1 alkyl.

[0103] In a preferred embodiment X is halide. Exemplary (meth)acryloyl halides include: acryloyl fluoride; acryloyl chloride; acryloyl bromide; acryloyl iodide; methacryloyl chloride; and, methacroyloyl bromide. The use of (meth)acryloyl chloride as the (meth)acrylating agent may be mentioned in particular. The reaction of this step ii) is depicted below:

##STR00010##

[0104] For completeness, within the compound of Formula (V) as depicted, substituents R.sup.2 to R.sup.5 have the meanings accorded above. R.sup.6 to R.sup.9 correspond to R.sup.6 to R.sup.9 save for the conversion of the n hydroxyl groups to (meth)acrylate groups. Thereby in Formula (V): [0105] R.sup.6 to R.sup.9 are independently selected from H, C.sub.1-C.sub.6 alkyl, C.sub.1-C.sub.6 alkoxy, C.sub.1-C.sub.12 alkoxyalkyl, SR.sup.12, COOR.sup.12 and N(R.sup.12)?; and, [0106] each R.sup.12 is independently selected from C.sub.1-C.sub.6 alkyl or C.sub.6-C.sub.18 aryl, [0107] subject to the proviso that n of radicals R.sup.6 to R.sup.9 are independently selected from R.sup.bOC(O)C(R.sup.13)CH.sub.2 wherein: [0108] R.sup.13 is H or C.sub.1 alkyl; [0109] n is an integer of from 1 to 3, preferably 1 or 2; and, [0110] for each of said n radicals, R.sup.b is independently selected from a covalent bond, C.sub.2-C.sub.12 alkylene, C.sub.3-C.sub.18 cycloalkylene or C.sub.6-C.sub.18 arylene.

[0111] The (meth)acrylating agent should be employed in an amount such that the number of moles of (meth)acrylate groups provided by said (meth)acrylating agent is at least equimolar with the number of moles of moles of hydroxyl groups provided by the compound of Formula (III). In some embodiments, it is preferred that the molar ratio of (meth)acrylate groups provided by said (meth)acrylating agent to hydroxyl groups provided by the compound of Formula (III) is from 1:1 to 2:1, for example from 1.1:1 to 1.5:1 or from 1.1:1 to 1.4:1. The provision of a stoichiometric excess of the (meth)acrylate groups can promote the complete reaction of the hydroxyl groups and can compensate for the reaction of said (meth)acrylate groups with any water entrained within the inert aprotic solvent.

[0112] Where the (meth)acrylating agent is a (meth)acryloyl halide, the reaction is desirably performed in the presence of a base which acts as a hydrogen-halide trap. The base would conventionally be employed in a supra-stoichiometric amount relative to the reactant (meth)acryloyl halide. Exemplary bases include but are not limited to: alkali metal hydroxides; alkali metal alkoxides, in particular C.sub.1-C.sub.4 aliphatic alkoxides of lithium sodium or potassium; alkaline earth metal hydroxides; and, tertiary amines.

[0113] The use of one or more tertiary amines is preferred in this regard. Without intention to limit the present disclosure, the utilized tertiary amines should be liquid under the reaction conditions. Alternatively or additionally, it is preferred for the or each tertiary amine used to be selected from tri(C.sub.1-C.sub.12)alkyl amines, di(C.sub.1-C.sub.12)alkyl(C.sub.3-C.sub.8) cycloalkyl amines or tri(C.sub.1-C.sub.10)alkenyl amines. A particular preference for the use of tri(C.sub.1-C.sub.12)alkyl amines may be mentioned, of which examples include but are not limited: trimethylamine; ethyldimethylamine; diethylmethylamine; triethylamine; triisopropylamine; tri-n-propylamine; tri-n-butylamine; tri-sec-butylamine; dibutylpentylamine; n-butyl-octyl-sec-butylamine; tripentylamine; and, trihexylamine.

[0114] This step is still further performed in the presence of inert aprotic solvent. Examples of suitable aprotic solvents, which may be used alone or in combination, include but are not limited to: pentane; hexane; heptanes; cyclopentane; cyclohexane; cycloheptane; dimethylether; chloroform; dimethyl carbonate; ethylmethyl carbonate; diethyl carbonate; toluene; o-xylene; m-xylene; p-xylene; ethylbenzene; 2-propylbenzene (cumene); 2-isopropyltoluene (o-cymol); 3-isopropyltoluene (m-cymol); 4-isopropyltoluene (p-cymol); 1,3,5-trimethylbenzene (mesitylene); acetonitrile; N,N-di(C.sub.1-C.sub.4)alkylacylamides, such as N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc); hexamethylphosphoramide; N-methylpyrrolidone; pyridine; esters, such as (C.sub.1-C.sub.5)alkyl acetates, ethoxydiglycol acetate, dimethyl glutarate, dimethyl maleate, dipropyl oxalate, ethyl lactate, benzyl benzoate, butyloctyl benzoate and ethylhexyl benzoate; ketones, such as acetone, ethyl ketone, methyl ethyl ketone (2-butanone) and methyl isobutyl ketone; ethers, such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF) and 1,2-dimethoxyethane; 1,3-dioxolane; dimethylsulfoxide (DMSO); and, dichloromethane (DCM).

[0115] Whilst it is not critical, it is preferred that the reaction of this step be performed under anhydrous conditions. Where necessary, exposure to atmospheric moisture may be avoided by providing the reaction vessel with an inert, dry gaseous blanket. Whilst dry nitrogen, helium and argon may be used as blanket gases, precaution should be used when common nitrogen gases are used as a blanket, because such nitrogen may not be dry enough on account of its susceptibility to moisture entrainment; the nitrogen may require an additional drying step before use herein.

[0116] The process pressure is not critical: as such, the reaction can be run at sub-atmospheric, atmospheric, or super-atmospheric pressures but pressures at or slightly above atmospheric pressure are preferred. Mention in this regard may be made of pressures of from 50 to 200 kPa, for example from 100 to 200 kPa.

[0117] The reaction temperature is typically from 40 to 20 C., for example from 20 to 20 C. As the reaction is generally exothermic, some cooling might be required as it progresses.

[0118] In certain embodiments, this stage of the reaction may be carried out in the presence of a polymerization inhibitor or a polymerization retarder. Polymerization inhibitors inhibit polymerization reactions from occurring and exemplary compounds which may have utility as inhibitors herein include: N,N-dialkylphenylenediamines; N,N-diarylphenylenediamines; N-aryl-N-alkylphenylene-diamines; and, quinone diimides. Polymerization retarders, while they slow down the rate of polymerization reactions, are not as effective as polymerization inhibitors in this context but, conversely, are consumed less rapidly. Exemplary polymerization retarders include quinone methide compounds, as disclosed in inter alia U.S. Pat. Nos. 4,003,800, 5,583,247 and 7,045,647. Combinations of a polymerization inhibitor and polymerization retarder are disclosed in US20200017610 A1 (Masere et al.).

[0119] The progress of the reaction of step ii) may be monitored by known techniques of which mention may be made of 1H NMR, Fourier Transform Infrared Spectroscopy, Ultra Performance Liquid Chromatography (UPLC) or thin layer chromatography (TLC). Upon completion of the reaction, the reaction mixture is washed with water and the organic product phase separated from the aqueous phase. The aprotic solvent may then be wholly or partially removed from that organic phase: this should be affected under reduced pressure and without elevating the temperature of the solution significantly above room temperature and, preferably, without exceeding 40 C. or even 35 C. The crude solid product may thus either be obtained following complete removal of the solvent or may be formed by subsequent cooling of a concentrated organic phase.

[0120] The crude solid product obtained may subsequently be purified by methods known in the art, including but not limited to solvent extraction, filtration, evaporation, distillation, (re-)crystallization and chromatography.

ILLUSTRATIVE EMBODIMENT OF THE METHOD

[0121] In accordance with an illustrative embodiment of the present disclosure, there is provided a method of preparing a compound of Formula (VA):

##STR00011## [0122] wherein: R.sup.6 to R.sup.9 are independently selected from H, C.sub.1-C.sub.4 alkyl, C.sub.1-C.sub.4 alkoxy, C.sub.1-C.sub.8 alkoxyalkyl, COOR.sup.12 and N(R.sup.12).sub.2; and, [0123] each R.sup.12 is independently selected from C.sub.1-C.sub.4 alkyl or C.sub.6-C.sub.18 aryl, [0124] subject to the proviso that n of radicals R.sup.6 to R.sup.9 are OC(O)C(R.sup.13)CH.sub.2 wherein R.sup.13 is H or C.sub.1 alkyl and further wherein n is an integer of 1 or 2, [0125] said method comprising the steps of: [0126] i) reacting a disulfide compound of Formula (IA) with a hydroxyl functional compound of Formula (II) to yield a compound of Formula (IIIA)

##STR00012## [0127] wherein: said reaction is performed in an acidic medium having a pH at or below 3.0; [0128] said reaction is performed at a temperature below the boiling point of the acidic medium and in the range from 40 to 120 C.; [0129] R.sup.6 to R.sup.9 correspond to said substituents R.sup.6 to R.sup.9 and are independently selected from the H, C.sub.1-C.sub.4 alkyl, C.sub.1-C.sub.4 alkoxy, C.sub.1-C.sub.8 alkoxyalkyl, COOR.sup.12 and N(R.sup.12).sub.2; [0130] R.sup.10 and R.sup.11 are H; and, [0131] each R.sup.12 is independently selected from C.sub.1-C.sub.4 alkyl or C.sub.6-C.sub.18 aryl, [0132] subject to the proviso that n of radicals R.sup.6 to R.sup.9 are OH, wherein n is an integer of 1 or 2; [0133] ii) reacting in an inert aprotic solvent said compound of Formula (IIIA) with a compound of Formula (IV) to yield said compound of Formula (VA)

##STR00013## [0134] wherein: X is chloride; [0135] the molar ratio of (meth)acrylate groups provided by said compound of Formula (IV) to hydroxyl groups provided by said compound of Formula (IIIA) is from 1.1:1 to 1.5:1; and, [0136] the reaction of step ii) is performed in the presence of a base selected from the group consisting of: tri(C.sub.1-C.sub.12)alkyl amines; di(C.sub.1-C.sub.12)alkyl(C.sub.3-C.sub.5) cycloalkyl amines; tri(C.sub.1-C.sub.10)alkenyl amines; and, mixtures thereof.

Formation of the Copolymers by Free Radical Polymerization

[0137] The present disclosure also provides for a polymer obtained by free radical polymerization of the compound of Formula (V) of which the compound of Formula (VA) is one example. In particular, the present disclosure provides a copolymer obtained by free radical polymerization, said copolymer comprising, based on the total weight of monomers: from 0.1 to 10 wt. % of a) at least one compound in accordance with Formula (V); and, from 90 to 99.9 wt. % of b) at least one ethylenically unsaturated non-ionic monomer which does not bear an epoxide group or a moiety decomposable under photo-irradiation to form a radical.

[0138] The copolymers of the present disclosure are prepared by free radical polymerization. As would be recognized by the skilled practitioner, free radical polymerization is constituted by three stages: initiation, wherein the decomposition of an initiator generates active free radicals which, possessing unpaired electrons, react with the monomers present to generating an initiating radicals chain; propagation, wherein the formed initiating radicals chain attacks a second monomer molecule transferring its active center to the attacked molecule, which process is repeated, growing the polymer chain; and, termination, wherein the growth of macromolecular chains stops, and the polymerization terminates by disabling the active center. The two most common termination mechanisms in radical polymerizations are combination and deprotonation.

[0139] Free radical polymerization may be performed in bulk, in emulsion, in suspension or in solution. Without specific intention to limit the present disclosure, the copolymers are preferably prepared by free radical solution polymerization: by this is meant that a solution of the monomers in a solvent, which is also capable of dissolving the copolymer is polymerized by a free radical polymerization, that is in the presence of the polymerization initiator. The concentration of the monomers in the solution may vary but it will be typical for the ratio by weight of monomer to solvent to be in the range from 1:20 to 2:1, for example from 1:2 to 1.5:1.

[0140] The free radical solution polymerization reaction should desirably be carried out in the presence of a polar solvent having a boiling point of at least 20 C., for instance at least 30 C. or at least 40 C., as measured at 1 atmosphere pressure (1.01325 Bar). Examples of such polar solvents, which may be used alone or in combination, include but are not limited to: water; C.sub.1-C.sub.8 alkanols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, sec-butanol and isobutanol; acetonitrile; N,N-di(C.sub.1-C.sub.4)alkylacylamides, such as N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc); hexamethylphosphoramide; N-methylpyrrolidone; pyridine; esters, such as (C.sub.1-C.sub.5)alkyl acetates, ethoxydiglycol acetate, dimethyl glutarate, dimethyl maleate, dipropyl oxalate, ethyl lactate, benzyl benzoate, butyloctyl benzoate and ethylhexyl benzoate; ketones, such as acetone, ethyl ketone, methyl ethyl ketone (2-butanone) and methyl isobutyl ketone; ethers, such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF) and 1,2-dimethoxyethane; 1,3-dioxolane; dimethylsulfoxide (DMSO); and, dichloromethane (DCM). In an exemplary embodiment, the polymerization reaction is performed in the presence of a (C.sub.1-C.sub.5)alkyl acetate and, in particular ethyl acetate.

[0141] As noted above, the free radical polymerization will be triggered by means of at least one radical generating thermal initiator. As will be understood by a person skilled in the art, a thermal initiator is a compound which can be activated by thermal energy to generate a radical thereof upon, for instance, heating or irradiation of the infrared or microwave wavelength regions. The polymerization composition should conventionally comprise from 0.1 to 1 wt. %, for example from 0.1 to 0.5 wt. % of said at least one radical generating thermal initiator, based on the total weight of the polymerizable monomers.

[0142] Without intention to limit the present invention, an exemplary class of radical generating thermal initiators suitable for use herein are organic peroxides, selected for example from: cyclic peroxides; diacyl peroxides; dialkyl peroxides; hydroperoxides; peroxycarbonates; peroxydicarbonates; peroxyesters; and, peroxyketals.

[0143] While certain peroxidessuch as dialkyl peroxideshave been disclosed as useful initiators in inter alia U.S. Pat. No. 3,419,512 (Lees) and U.S. Pat. No. 3,479,246 (Stapleton) and indeed may have utility herein, hydroperoxides represent a preferred class of initiator for the present invention. Further, whilst hydrogen peroxide itself may be used, the most desirable polymerization initiators are the organic hydroperoxides. For completeness, included within the definition of hydroperoxides are materials such as organic peroxides or organic peresters which decompose or hydrolyze to form organic hydroperoxides in situ: examples of such peroxides and peresters are cyclohexyl and hydroxycyclohexyl peroxide and t-butyl perbenzoate, respectively.

[0144] In an embodiment of the invention, the radical generating thermal initiator comprises or consists of at least one hydroperoxide compound represented by the formula:

R.sup.pOOH [0145] wherein: R.sup.p is an aliphatic or aromatic group containing up to 18 carbon atoms, and preferably wherein: R.sup.p is a C.sub.1-C.sub.12 alkyl, C.sub.6-C.sub.18 aryl or C.sub.7-C.sub.18 aralkyl group.

[0146] As exemplary peroxide initiators, which may be used alone or in combination, there may be mentioned: cumene hydroperoxide (CHP); para-menthane hydroperoxide; t-butyl hydroperoxide (TBH); t-butyl perbenzoate; t-butyl peroxy pivalate; di-t-butyl peroxide; t-butyl peroxy acetate; t-butyl peroxy-2-hexanoate; t-amyl hydroperoxide; 1,2,3,4-tetramethylbutyl hydroperoxide; benzoyl peroxide; dibenzoyl peroxide; 1,3-bis(t-butylperoxyisopropyl)benzene; diacetyl peroxide; butyl 4,4-bis(t-butylperoxy) valerate; p-chlorobenzoyl peroxide; t-butyl cumyl peroxide; di-t-butyl peroxide; dicumyl peroxide; 2,5-dimethyl-2,5-di-t-butylperoxyhexane; 2,5-dimethyl-2,5-di-t-butyl-peroxyhex-3-yne; and, 4-methyl-2,2-di-t-butylperoxypentane.

[0147] Without intention to limit the present invention, a further exemplary class of radical generating thermal initiators suitable for use herein are azo polymerization initiators, selected for example from: azo nitriles; azo esters; azo amides; azo amidines; azo imidazoline; and, macro azo initiators.

[0148] As representative examples of suitable azo polymerization initiators may be mentioned: 2,2-azobis (2-methylbutyronitrile): 2,2-azobis(isobutyronitrile): 2,2-azobis(2,4-dimethylvaleronitrile): 2,2-azobis(4-methoxy-2,4-dimethylvaleronitrile): 1,1-azobis(cyclohexane-1-carbonitrile): 4,4-azobis(4-cyanovaleric acid): dimethyl 2,2-azobis(2-methylpropionate); 2,2-azobis [2-methyl-N-(2-hydroxyethyl)propionamide]: 2,2-azobis(N-butyl-2-methylpropionamide): 2,2-azobis [2-(2-imidazolin-2-yl)propane]dihydrochloride: 2,2-azobis [2-(2-imidazolin-2-yl)propane]: 2,2-azobis(2-methylpropionamidine) dihydrochloride: 2,2-azobis [N-(2-carboxyethyl)-2-methylpropionamidine]tetrahydrate; 4,4-azobis(4-cyanovaleric acid), polymer with alpha, omega-bis(3-aminopropyl) polydimethylsiloxane (VPS-1001, available from Wako Pure Chemical Industries, Ltd.); and, 4,4-azobis(4-cyanopentanoicacic).Math.polyethyleneglycol polymer (VPE-0201, available from Wako Pure Chemical Industries, Ltd.).

[0149] Redox initiators are a combination of an oxidizing agent and a reducing agent and may also have utility in the present invention. Suitable oxidizing agents may be selected from the group consisting of cyclic peroxides, diacyl peroxides, dialkyl peroxides, hydroperoxides, peroxycarbonates, peroxydicarbonates, peroxyesters and peroxyketals. The corresponding reducing agent may be selected from the group consisting of: alkali metal sulfites; alkali metal hydrogensulfites; alkali metal metabisulfites; formaldehyde sulfoxylates; alkali metal salts of aliphatic sulfinic acids; alkali metal hydrogensulfides; salts of polyvalent metals, in particular Co(II) salts and Fe(II) salts such iron(II) sulfate, iron(II) ammonium sulfate or iron(II) phosphate; dihydroxymaleic acid; benzoin; ascorbic acid; and, reducing saccharides, such as sorbose, glucose, fructose and/or dihydroxyacetone.

[0150] Aside from initiators, it is considered that the free radical polymerization may be conducted in the presence of chain transfer agents which act to transfer free radicals and which reduce the molecular weight of the obtained polymer and/or control chain growth in the polymerization. When added, the chain transfer agent should constitute from 0.01 to 1 wt. %, based on the total weight of polymerizable monomers.

[0151] The process for producing the copolymer is preferably carried out in a manner that the copolymer has a number average molecular weight (Mn) of from 50000 to 500000 Daltons, for example from 75000 to 300000 Daltons or from 100000 to 250000 Daltons. The amount of polymerization initiator and any chain transfer agents present will be determinative of the number average molecular weight of the copolymer, although the choice of solvent may also be important.

[0152] Without intention to limit the present invention, conventional polymerization conditions will include a temperature in the range of from 0 to 175 C., for example from 25 to 125 C. or from 50 to 100 C. The polymerization pressure is generally not critical and, as such, the polymerization may be conducted at sub-atmospheric, atmospheric or super-atmospheric pressure. Pressure aside, the polymerization may be conducted, where necessary, under the exclusion of oxygen: the reaction vessel may be provided with an inert, dry gaseous blanket of, for example, nitrogen, helium and argon.

[0153] For completeness, it is considered that the present polymerization may be performed as a batch or semi-batch procedure or as a continuous procedure. As would be recognized by the skilled artisan, in the batch procedure, the monomers to be polymerized and optionally the solvent used in the polymerization procedure are charged to a reaction vessel, while the majority or the total amount of the polymerization initiator is added to the reaction vessel over the course of the polymerization. In a semi-batch procedure, at least a portionup to and including the total amountof the polymerization initiator and solvent are initially charged to the reaction vessel: a small portion of the monomers may also be so-charged but the majority of monomers to be polymerized are added to the reaction vessel over the course of the polymerization. In a continuous process the monomers, polymerization initiator and, optionally, the solvent are continuously added to a reaction vessel and the obtained polymer is continuously discharged from the polymerization vessel.

[0154] A preference may be mentioned for the performance of the present polymerization as a semi-batch procedure. In particular, at least 75 wt. % of the total weight of monomers to be polymerized should be added to the reaction vessel over the course of the polymerization reaction.

[0155] There is no particular intention to limit the timing at which the different functional monomerspart a) and part b)of the copolymer are introduced into the polymerization procedure. The monomers may be provided to the polymerization vessel at a fixed molar ratio either at the start of the polymerization (for a batch process) or through the entire polymerization process (for semi-batch and continuous processes). In the alternative, the molar ratio of the monomers types may be varied during the course of the polymerization: this is intended to encompass that embodiment where, during the course of the polymerization, only the monomers of part a) are added to the polymerization vessel or conversely only monomers of part b) are added to the polymerization vessel. The skilled artisan may make determinations of suitable molar ratios based on the desired form or randomness of the copolymer and the reactivity ratios of the monomers.

[0156] The copolymer reaction product may be isolated and purified using methods known in the art, of which mention may be made of extraction, evaporation, crystallization, distillation and chromatography as suitable techniques. Where a free radical solution polymerization is performed, it is most convenient that the copolymer be isolated by distilling off the solvent and any unreacted starting materials under reduced pressure. Where it is intended that the (optionally purified) copolymer be stored upon production, the polymers should be disposed in a vessel with an airtight and moisture-tight seal. The storage vessel should not permit the penetration of photo-irradiation.

[0157] The following examples are illustrative of the present invention and are not intended to limit the scope of the invention in any way.

EXAMPLES

[0158] The following commercial compounds are used in the Example:

Example 1: Synthesis of 2-hydroxy-3-(propan-2-yl)-9H-thioxanthen-9-one

##STR00014##

[0159] 5.0 g (16.33 mmol) of 2,2-dithiobenzoic acid was suspended in 50 ml of concentrated (95%) sulfuric acid. 13 g (95.5 mmol) of 2-(propan-2-yl) phenol was added to the suspension over 10 minutes: within this time, the mixture was heated to approximately 50 C. The reaction mixture was then heated to 80 C., which temperature was maintained for three hours. After that time, the mixture was cooled to room temperature and stirred overnight. The obtained mixture was added dropwise into 500 ml of boiling, deionized water. The resultant precipitate was filtered off and washed once with 50 ml of boiling water and once with 100 ml of cold water. The resulting product was dried under vacuum. Product: green powder; ca. 50% yield.

Example 2: Synthesis of 9-oxo-3-(propan-2-yl)-9H-thioxanthen-2-yl prop-2-enoate

##STR00015##

[0160] 5 g (18.5 mmol) of 2-hydroxy-3-(propan-2-yl)-9H-thioxanthen-9-one was dissolved in 200 ml of dry dichloromethane. After the addition of 4 g (39.5 mmol) of triethylamine, the reaction mixture was cooled to 0 C. under stirring and a nitrogen atmosphere. 2 ml (24.5 mmol) of acryloyl chloride was added dropwise through a septum. After stirring for 4 hours at 0 C., the reaction mixture was further stirred overnight at room temperature. The obtained mixture was carefully washed twice with 50 ml of deionized water. The organic phase was concentrated on a rotavapor to a volume of approximately 15 ml whilst not exceeding 40 C. After cooling to 0 C., the precipitate was filtered off and washed with methanol. The filtered product was recrystallized from methanol and dried under vacuum. Product: yellow powder; ca. 50% yield.

Example 3: Synthesis of 2-hydroxy-1,3-dimethyl-9H-thioxanthen-9-one

##STR00016##

[0161] 5.0 g (16.33 mmol) of 2,2-dithiobenzoic acid was suspended in 50 ml of concentrated (95%) sulfuric acid. 95.5 mmol of 2,6-dimethylphenol was added to the suspension over 10 minutes: within this time, the mixture was heated to approximately 50 C. The reaction mixture was then heated to 80 C., which temperature was maintained for three hours. After that time, the mixture was cooled to room temperature and stirred overnight. The obtained mixture was added dropwise into 500 ml of boiling, deionized water. The resultant precipitate was filtered off and washed once with 50 ml of boiling water and once with 100 ml of cold water. The resulting product was dried under vacuum. Product: green powder; ca. 50% yield.

[0162] The obtained 2-hydroxy-1,3-dimethyl-9H-thioxanthen-9-one was reacted with acryloyl chloride in accordance with the procedure of Example 2.

Example 4: Synthesis of 1-hydroxy-4-(2-methoxyethyl)-9H-thioxanthen-9-one

##STR00017##

[0163] 5.0 g (16.33 mmol) of 2,2-dithiobenzoic acid was suspended in 50 ml of concentrated (95%) sulfuric acid. 95.5 mmol of 4-(2-methoxyethyl) phenol was added to the suspension over 10 minutes: within this time, the mixture was heated to approximately 50 C. The reaction mixture was then heated to 80 C., which temperature was maintained for three hours. After that time, the mixture was cooled to room temperature and stirred overnight. The obtained mixture was added dropwise into 500 ml of boiling, deionized water. The resultant precipitate was filtered off and washed once with 50 ml of boiling water and once with 100 ml of cold water. The resulting product was dried under vacuum. Product: green powder; ca. 50% yield.

[0164] The obtained 1-hydroxy-4-(2-methoxyethyl)-9H-thioxanthen-9-one was reacted with acryloyl chloride in accordance with the procedure of Example 2.

Example 5:3-acetyl-2-hydroxy-9H-thioxanthen-9-one

##STR00018##

[0165] 5.0 g (16.33 mmol) of 2,2-dithiobenzoic acid was suspended in 50 ml of concentrated (95%) sulfuric acid. 95.5 mmol of 1-(2-hydroxyphenyl) ethan-1-one was added to the suspension over 10 minutes: within this time, the mixture was heated to approximately 50 C. The reaction mixture was then heated to 80 C., which temperature was maintained for three hours. After that time, the mixture was cooled to room temperature and stirred overnight. The obtained mixture was added dropwise into 500 ml of boiling, deionized water. The resultant precipitate was filtered off and washed once with 50 ml of boiling water and once with 100 ml of cold water. The resulting product was dried under vacuum. Product: green powder; ca. 50% yield.

[0166] The obtained 3-acetyl-2-hydroxy-9H-thioxanthen-9-one was reacted with acryloyl chloride in accordance with the procedure of Example 2.

Example 6: Synthesis of 3-(dimethylamino)-1-hydroxy-9H-thioxanthen-9-one

##STR00019##

[0167] 5.0 g (16.33 mmol) of 2,2-dithiobenzoic acid was suspended in 50 ml of concentrated (95%) sulfuric acid. 95.5 mmol of 3-(dimethylamino) phenol was added to the suspension over 10 minutes: within this time, the mixture was heated to approximately 50 C. The reaction mixture was then heated to 80 C., which temperature was maintained for three hours. After that time, the mixture was cooled to room temperature and stirred overnight. The obtained mixture was added dropwise into 500 ml of boiling, deionized water. The resultant precipitate was filtered off and washed once with 50 ml of boiling water and once with 100 ml of cold water. The resulting product was dried under vacuum. Product: green powder; ca. 50% yield.

[0168] The obtained 3-(dimethylamino)-1-hydroxy-9H-thioxanthen-9-one was reacted with acryloyl chloride in accordance with the procedure of Example 2.

Example 7:2-hydroxy-9-oxo-9H-thioxanthene-3-carboxylate

##STR00020##

[0169] 5.0 g (16.33 mmol) of 2,2-dithiobenzoic acid was suspended in 50 ml of concentrated (95%) sulfuric acid. 95.5 mmol of 2-hydroxybenzoate was added to the suspension over 10 minutes: within this time, the mixture was heated to approximately 50 C. The reaction mixture was then heated to 80 C., which temperature was maintained for three hours. After that time, the mixture was cooled to room temperature and stirred overnight. The obtained mixture was added dropwise into 500 ml of boiling, deionized water. The resultant precipitate was filtered off and washed once with 50 ml of boiling water and once with 100 ml of cold water. The resulting product was dried under vacuum. Product: green powder; c. 50% yield.

[0170] The obtained 2-hydroxy-9-oxo-9H-thioxanthene-3-carboxylate was reacted with acryloyl chloride in accordance with the procedure of Example 2.

Example 8: Synthesis of 3-ethoxy-2-hydroxy-9H-thioxanthen-9-one

##STR00021##

[0171] 5.0 g (16.33 mmol) of 2,2-dithiobenzoic acid was suspended in 50 ml of concentrated (95%) sulfuric acid. 95.5 mmol of 2-ethoxyphenol was added to the suspension over 10 minutes: within this time, the mixture was heated to approximately 50 C. The reaction mixture was then heated to 80 C., which temperature was maintained for three hours. After that time, the mixture was cooled to room temperature and stirred overnight. The obtained mixture was added dropwise into 500 ml of boiling, deionized water. The resultant precipitate was filtered off and washed once with 50 ml of boiling water and once with 100 ml of cold water. The resulting product was dried under vacuum. Product: green powder; c. 50% yield.

[0172] The obtained 3-ethoxy-2-hydroxy-9H-thioxanthen-9-one was reacted with acryloyl chloride in accordance with the procedure of Example 2.

[0173] In view of the foregoing description and example, it will be apparent to those skilled in the art that equivalent modifications thereof can be made without departing from the scope of the claims.