WO2017117124A1

WO2017117124A1 - Crosslinkable hole transport molecule having four radical polymerizable groups and method to make the same

Info

Publication number: WO2017117124A1
Application number: PCT/US2016/068704
Authority: WO
Inventors: David Glenn Black; Weimei Luo; Kelly Ann Killeen
Original assignee: Lexmark International, Inc.
Priority date: 2015-12-29
Filing date: 2016-12-27
Publication date: 2017-07-06

Abstract

A crosslinkable hole transport molecule having four radical polymerizable groups to be used in a photoconductor to provide a medium for hole transport upon exposure to light and method to make the same is provided. Photoconductors using this hole transport molecule have improved mechanical wear resistance and excellent electrical properties. The crosslinkable hole transport molecule containing four radical polymerizable functional groups has the general structure exemplified below:

Description

CRO S SLINKABLE HOLE TRANSPORT MOLECULE HAVING FOUR RADICAL POL YMERIZ ABLE GROUPS AND METHOD TO MAKE THE SAME

CROSS REFERENCES TO RELATED APPLICATIONS

[0001] None

[0002] BACKGROUND

[0003] 1. Field of the Disclosure

[0004] The present disclosure relates generally to photoconductors used in electrophotographic image forming devices and more particularly to a novel crosslinkable hole transport molecule having four radical polymerizable groups to be used in a photoconductor to provide a medium for hole transport upon exposure to light and method to make the same. Photoconductors using this novel hole transport molecule have improved mechanical wear resistance and excellent electrical properties.

[0005] 2. Description of the Related Art

[0006] In electrophotography, a latent image is created on the surface of an imaging member such as a photoconducting material by first uniformly charging the surface and then selectively exposing areas of the surface to light. A difference in electrostatic charge density is created between those areas on the surface which are exposed to light and those areas on the surface which are not exposed to light. The latent electrostatic image is developed into a visible image by electrostatic toners. The toners are selectively attracted to either the exposed or unexposed portions of the photoconductor surface, depending on the relative electrostatic charges on the photoconductor surface, the development electrode and the toner. Electrophotographic photoconductors may be a single layer or a laminate formed from two or more layers (multilayer type and configuration).

[0007] A dual layer electrophotographic photoconductor comprises a substrate such as a metal ground plane member on which a charge generation layer (CGL) and a charge transport layer (CTL) are coated. A single layer electrophotographic photoconductor combines the charge generator and the charge transport functions into a single layer in the photoconductor. The charge transport layer contains a charge transport material which comprises a hole transport material or an electron transport material.

[0008] Conventionally, the charge generation layer comprises the charge generation compound or molecule alone and/or in combination with a binder. A charge transport layer typically comprises a polymeric binder and a charge or hole transport compound or molecule (hereinafter 'hole'transport compound or molecule). The charge generation compounds within the charge generation layer are sensitive to image-forming radiation and photogenerate electron hole pairs therein as a result of absorbing such radiation. The charge transport layer is usually non- absorbent of the image-forming radiation and the hole transport compounds serve to transport holes to the surface of a negatively charged photoconductor.

[0009]Charge generation layers are generally prepared by dispersing a pigment (e.g.,

phthalocyanines, azo compounds, squaraines, etc.) in a polymeric matrix. Since the pigment or dye in the charge generation layer typically does not have the capability of binding or adhering effectively to a metal substrate, a polymer binder is often employed. This polymer binder is usually inert to the electrophotographic process, but forms a stable dispersion with the pigment/dye and has good adhesive properties to the metal substrate. The electrical sensitivity associated with the charge generation layer can be affected by the nature of polymeric binder used.

[0010] Additionally, photoconductors can be overcoated with a formulation having hole transport molecules dispersed within the overcoat formulation. An overcoat formulation comprising a radical polymerizable hole transport molecule in combination with hexafunctional urethane acrylates is disclosed in US Patent No. 8,940,466 entitled PHOTOCONDUCTOR OVERCOATS COMPRISING RADICAL POLYMERIZABLE CHARGE TRANSPORT MOLECULES AND HEXA FUNCTIONAL URETHANE ACRYLATES, which is assigned to the assignee of the present application and is incorporated by reference herein in its entirety. [OOllJKnown prior art hole transport molecules utilized in photoconductors contribute to the undesirable deficiencies found in photoconductors such as decrease mechanical wear resistance and resistance to stress cracking and not maintaining the good electrical properties of the photoconductor.

[0012] SUMMARY

[0013] The present disclosure provides a novel crosslinkable hole transport molecule having four radical polymerizable functional groups and method to make the same. Photoconductors using this particular crosslinkable hole transport molecule have improved mechanical wear resistance and excellent electrical properties. Importantly, photoconductors using this novel crosslinkable hole transport molecule have an 'ultra long life', whereby they can print at a minimum of 250,000 pages before the consumer has to purchase a costly replacement photoconductor. In other words, the photoconductor will no longer be a replaceable unit nor be viewed as a consumable item that has to be purchased multiple times by the consumer. Photoconductor having an 'ultra long life' allow the printer to operate with a lower cost-per-page, more stable image quality, and less waste leading to a greater customer satisfaction with his or her printing experience. Additionally photoconductors using this crosslinkable hole transport molecule having four radical polymerizable groups also have excellent electrical properties.

[0014]The general structure of the crosslinkable hole transport molecule having four radical polymerizable functional groups of the present invention is exemplified below:

wherein R¹ is a radical polymerizable group, the groups R², R³, and R⁴ may be the same or different, and wherein each of R², R³, and R⁴ are independently selected from the group consisting of (i) hydrogen, (ii) an alkyl group, which can be linear or branched, saturated or unsaturated, cyclic or acyclic, substituted or unsubstituted alkyl, (iii) an aryl group, which can be substituted or unsubstituted aryl, (iv) an arylalkyl group, which can be substituted or

unsubstituted arylalkyl, wherein the alkyl portion of the arylalkyl can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted , (v) an alkylaryl group, which can be substituted or unsubstituted alkylaryl, wherein the alkyl portion of the alkylaryl can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted, (vi) an alkoxy group, (vii) an aryloxy group, which can be substituted or unsubstituted aryloxy, (viii) an arylalkyloxy group, which can be substituted or unsubstituted arylalkyloxy, wherein the alkyl portion of the arylalkyloxy can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted, and (ix) an alkylaryloxy group, which can be substituted or unsubstituted alkylaryloxy, wherein the alkyl portion of the alkylaryloxy can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted. In one embodiment, the radical polymerizable group R^!is an acrylate group, R² and R⁴ are hydrogen and R³ is a methyl group. [0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings incorporated in and forming a part of the specification, illustrate several aspects of the present disclosure, and together with the description serve to explain the principles of the present disclosure.

[0017] Figure 1 shows the photo induced discharge (PID) curves of a photoconductor drum having the crosslinkable hole transport molecule having four radical polymerizable functional groups and a prior art photoconductor drum having a different hole transport molecule.

[0018] DETAILED DESCRIPTION

[0019] It is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the

phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Further, the terms "a" and "an" herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item.

[0020] The terms "crosslinkable" and "radical polymerizable," and derivatives thereof, may be used interchangeably. "Substantially crosslinked" in embodiments refers to, for example, a state in which about 60% to 100% of the hole transport compounds for example about 70% to 100%) or about 80%> to 100%>, are covalently bound. A crosslinkable hole transport molecule may be understood as any compound that 1) contributes to surface charge retention in the dark, 2) possesses radical crosslinkable functionality and, 3) provides a medium for hole transport upon exposure to light. In one example embodiment, the crosslinkable hole transport molecule may include organic materials capable of accepting and transporting charges.

[0021] In an example embodiment, the hole transport molecule is crosslinkable and has four radical polymerizable functional groups or tetrafunctionality. The general structure of this tetrafunctional crosslinkable hole transport molecule containing four radical polymerizable functional groups is exemplified below:

wherein R³ is a radical polymerizable functional group selected from the group consisting of acrylate group, methacrylate group, allylic group, glycidyl ether group and epoxy group. The

2 3 4 2 3 4 groups R R and may be the same or different, and wherein each of R , R , and R are independently selected from the group consisting of (i) hydrogen, (ii) an alkyl group, which can be linear or branched, saturated or unsaturated, cyclic oracyclic, substituted or unsubstituted alkyl, (iii) an aryl group, which can be substituted or unsubstituted aryl , (iv) an arylalkyl group, which can be substituted or unsubstituted arylalkyl, wherein the alkyl portion of the arylalkyl can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or

unsubstituted, (v) an alkylaryl group, which can be substituted or unsubstituted alkylaryl, wherein the alkyl portion of the alkylaryl can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted, (vi) an alkoxy group, (vii) an aryloxy group, which can be substituted or unsubstituted aryloxy , (viii) an arylalkyloxy group, which can be substituted or unsubstituted arylalkyloxy, wherein the alkyl portion of the arylalkyloxy can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted, and (ix) an alkylaryloxy group, which can be substituted or unsubstituted alkylaryloxy, wherein the alkyl portion of the alkylaryloxy can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted.

[0022] The radical polymerizable functional group R¹ can be any radical polymerizable functional group capable of undergoing crosslinking reactions upon exposure to light or e-beam radiation. The radical polymerizable functional group is selected from the group consisting of acrylate group, methacrylate group, allylic group, glycidyl ether group and epoxy group. In one embodiment, the radical polymerizable group R^xis an acrylate group. In one embodiment, R² and R⁴ are hydrogen and R³ is a methyl group. The structure of the disclosed crosslinkable hole transport molecule described hereinabove wherein R'is an acrylate group, R²and R⁴ are hydrogen and R³ is a methyl group is exemplified below:

[0023] The crosslinkable hole transport molecule containing four radical polymerizable functional groups of the present invention provides both the necessary charge transporting properties with the added abrasion resistance needed in an electrophotographic printer. In an electrophotographic printer, such as a laser printer, an electrostatic image is created by illuminating a portion of the photoconductor surface in an image-wise manner. The wavelength of light used for this illumination is most typically matched to the absorption max of a charge generation material, such as titanylphthalocyanine. Absorption of light results in creation of an electron-hole pair. Under the influence of a strong electrical field, the electron and hole (radical cation) dissociate and migrate in a field-directed manner. Photoconductors operating in a negative charging manner move holes to the surface and electrons to ground. The holes discharge the photoconductor surface, thus leading to creation of the latent image. When utilized in a photoconductor, the crosslinkable hole transport molecules having four radical

polymerizable functional groups of the present invention provide photoconductors with improved abrasion and mechanical wear resistance and excellent electrical properties.

[0024] Synthesis of an Inventive Crosslinkable Hole Transport Molecule Having Four Radical Polymerizable Groups

[0025] The general synthetic scheme for the synthesis of a novel crosslinkable hole transport molecule having four radical polymerizable groups involves performing the following steps:

(1) a Buchwald-Hartwig amination reaction of an aryl halide having a protected aldehyde with a primary arylamine in the presence of a base, palladium precursor, ligand and solvent to form a triarylamine having two protected aldehyde groups.

(2) a deprotection of the triarylamine having two protected aldehyde groups to form a triarylamine dialdehyde;

(3) a condensation of the triarylamine dialdehyde with a dialkylmalonate to form a triarylamine tetraester;

(4) a reduction of the triarylamine tetraester to form a triarylamine tetraol; and (5) an introduction of crosslinking functionality to the triarylamine tetraol to form a tetrafunctional triarylamine. In an embodiment, the introduction of crosslinking functionality is done by acrylation.

[0026] The general synthesis of the novel crosslinkable hole transport molecule having tetrafunctionality described in the preceding Steps 1 through 5 is also set forth in the following equations:

Equation 1

Equation 2

Equation 3

Equation 4

Equation 5

[0027] The following paragraphs set forth a detailed explanation of the synthesis of the novel crosslinkable hole transport molecule having tetrafunctionality.

[0028] Step 1 is a Buchwald-Hartwig amination reaction of an aryl halide having a protected aldehyde group with a primary arylamine in the presence of a base, palladium precursor, ligand and solvent. The novel synthesis of the crosslinkable hole transport molecule incorporates a protected aldehyde group because the conditions of the Buchwald-Hartwig reaction may lead to an undesirable Schiff base reaction between the primary arylamine and an unprotected aldehyde group.

The aryl halide may be an aryl chloride, aryl bromide or aryl iodide. In an embodiment, the aryl halide is an aryl bromide.

[0029] As outlined above, the aryl halide has a protected aldehyde group. Regiochemically, the aldehyde protecting group can be substituted in the para position, the meta position or any combination thereof. In an embodiment, the aldehyde protecting group is in the para position relative to the halide of the aryl halide. In another embodiment the aldehyde protecting group is in the meta position relative to the halide of the aryl halide. The aldehyde protecting group used must be stable under the basic conditions of the Buchwald-Hartwig reaction performed in Step 1. Examples of useful aldehyde protection groups include, but are not limited to cyclic acetals, acyclic dialkyl acetals, 1, 3 dithianes, 1,3 dithiolanes, thioacetals, thioketals, and oximes. In an embodiment, the aldehyde protecting group is a dialkyl acetal such as dimethylacetal.

[0030] The primary arylamine used in the Buchwald-Hartwig reaction of Step 1 may be substituted in the para position, the meta positions or any combination thereof. The substituents in the meta and para positions are independently selected from the group consisting of (i) hydrogen, (ii) an alkyl group, which can be linear or branched, saturated or unsaturated, cyclic or acyclic, substituted or unsubstituted alkyl, (iii) an aryl group, which can be substituted or unsubstituted aryl, (iv) an arylalkyl group, which can be substituted or unsubstituted arylalkyl, wherein the alkyl portion of the arylalkyl can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted , (v) an alkylaryl group, which can be substituted or unsubstituted alkylaryl, wherein the alkyl portion of the alkylaryl can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted, (vi) an alkoxy group, (vii) an aryloxy group, which can be substituted or unsubstituted aryloxy, (viii) an arylalkyloxy group, which can be substituted or unsubstituted arylalkyloxy, wherein the alkyl portion of the arylalkyloxy can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted; and (ix) an alkylaryloxy group, which can be substituted or unsubstituted alkylaryloxy, wherein the alkyl portion of the alkylaryloxy can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted. In an embodiment, the primary arylamine is substituted with hydrogen atoms in the meta positions, and an alkyl group such as a methyl group in the para position.

[0031] The base used in the Buchwald-Hartwig reaction of Step 1 may be any base capable of removing a proton from a primary or a secondary arylamine. Examples of bases include, but are not limited to tert-BuOK, fert-BuONa, Cs₂C0₃, lithium bis(trialkylsilyl)amide, KOH, NaOH, NaOMe, K₂C0₃ or K₃P0₄. Those skilled in the art will understand that the bases exemplified above may be used alone or in combination. In an embodiment, the base is tert-BuONa. [0032] The palladium precursor used in the Buchwald-Hartwig reaction of Step 1 is any source of palladium capable of catalyzing the Buchwald-Hartwig reaction in the presence of the appropriate ligand. The palladium precursor should have an oxidation state of 0, (PdfO)), or be capable of being reduced to Pd(0) under the reaction conditions. In the event that the palladium precursor is not Pd(0), but rather, for example, Pd(Ii), addition of a small amount of a reducing agent may be required to generate the Pd (0). Suitable reducing agents include, but are not limited to tertiary amines or boronic acids. Addition of small amounts of reducing agent(s) required to reduce Pd(II) to Pd(0) are regarded as falling within the scope of the present invention. Examples of Pd(0) sources include, but are not limited to

tris(dibenzylideneacetone)dipalladium (Pd₂(dba)₃), and bis(dibenzylideneacetone)pailadium (Pd(dba)₂). Sources of Pd(II) include, but are not limited to palladium chloride, palladium bromide, palladium iodide, palladium acetate, palladium acetyl acetonate, palladium

hexafluoroacetylacetonate, palladium trifluoroacetate, ally! palladium chloride dimer, (2,2 - bipyridine)dichloropalladium, bis(benzonitrile)dichloropalladium,

bisiacetonitriie dichloiOpalladium, (bicyclo[2.2.1]hepta-2,5-diene)dichloropalladium, di eh!oro( I , 5 -cy ciooctadiene)pal ί adium, dibromobi s(triph eny!ph osphine)pal ί adium,

di chloro(N,N, ',Ν'-tetramethyl ethyl enediamine)pali adium, dichl oro( 1,10- ph enathroii nejpalladi urn, di chlorobi s(tri phenyl phosphin epall adi urn), ammonium

tetrachloropalladate, diaminedibromopalladium, diaminedichloropalladium,

diaminediiodopalladium, potassium tetrabromopalladate, potassium tetrachloropalladate and sodium tetrachloropalladate. Those skilled in the art will understand that the palladium precursors exemplified above may be used alone or in combination. In an embodiment, the palladium precursor is tris(dibenzylideneacetone)dipalladium.

[0033] The ligand used in the Buchwald-Hartwig reaction of Step 1 is any molecule capable of coordinating to the palladium precursor and facilitating the Buchwald-Hartwig reaction. These ligands include, but are not limited to dialkylbiarylphosphines, ferrocenyl diphenyl, dialkyl phosphines and bulky, electron rich phosphines. Examples of dialkylbiarylphosphine ligands include: 2-Dicyclohexylphosphino-2'-(N,N-dimethylamino)biphenyl (DavePhos), 2- Dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl (Xphos), 2-Dicyclohexylphosphino-2',6'- dimethoxybiphenyl (Sphos), 2-Di-tert-butylphosphino-2',4',6'-triisopropylbiphenyl (tBuXPhos), (2-Biphenyl)dicyclohexylphosphine, 2-(Dicyclohexylphosphino)biphenyl (CyJohnPhos), (2- Biphenyl)di-tert-butylphosphine (JohnPhos), 2-Dicyclohexylphosphino-2',6'- diisopropoxybiphenyl (RuPhos), 2-Di-tert-butylphosphino-2'-methylbiphenyl (tBuMePhos), 2- Di-tert-butylphosphino-3,4,5,6-tetramethyl-2',4',6'-triisopropyl-l, -biphenyl 2-Di^'-tert- butylphosphino-2'-methylbiphenyl (tBuMePhos), 2-Di-tert-butylphosphino-3,4,5,6-tetramethyl- 2',4',6'-triisopropyl-l, -biphenyl (Tetramethyl tBuXPhos), and 2-(Dicyclohexylphosphino)3,6- dimethoxy-2',4',6'-triisopropyl-l, l '-biphenyl (BrettPhos). Examples ferrocenyl diphenyl and dialkyl phosphines include: l,l '-Ferrocenediyl-bis(diphenylphosphine) (dppf), 1,2,3,4,5- Pentaphenyl- 1 '-(di-tert-butylphosphino)ferrocene (Q-Phos), 1 , 1 '-Bis(di-tert- butylphosphino)ferrocene, l,l '-Bis(dicyclohexylphosphino)ferrocene and 1, 1 '- Bis(diisopropylphosphino)ferrocene. An example of a bulky, electron rich phosphine is \A-tert- butylphosphine. An air stable variant of the tri-tert-butylphosphine ligand is tn-tert- butylphosphonium tetrafluorob orate. Those skilled in the art will understand that the ligands exemplified above may be used alone or in combination. In an embodiment, the ligand is tri- tert-butylphosphonium tetrafluorob orate.

[0034] The solvent used in the Buchwald-Hartwig reaction of Step 1 is any non-halogenated organic solvent, so long as it is free of moisture. Halogenated solvents may react in the

Buchwald-Hartwig animation and thus lower the yield of the desired product. Water molecules can also react with the aryl halide to produce aryl alcohols (phenols), thus lowering the yield of the expected product. Common organic solvents include, but are not limited to cyclic ethers such as tetrahydrofuran (THF), ethers such as diethyl ether or fer/-butyl methyl ether aromatic solvents such as toluene or xylene, acetate solvents such as ethyl acetate or butyl acetate, aliphatic solvents such as hexane or decane, and amide solvents such as dimethyl formamide (DMF), dimethyl acetamide (DMAc) and N-methylpyrrolidone (NMP). Those skilled in the art will understand that the solvents exemplified above may be used alone or in combination. In an embodiment, the solvent is toluene.

[0035] Step 2 is the deprotection of the resulting triarylamine having two protected aldehyde groups formed in Step 1 to form a triarylamine dialdehyde. The aldehyde deprotecting agent is used to generate the triarylamine dialdehyde upon completion of the Buchwald-Hartwig reaction described in Step 1. The choice of aldehyde deprotecting agent will depend upon the aldehyde protecting group chosen. Examples of aldehyde deprotecting agents include, but are not limited to aqueous strong acids such as aqueous HC1 and aqueous HBr, and Lewis acids such as Er(OTf)3 and CuCl₂. Those skilled in the art will understand that the aldehyde deprotecting agents exemplified above may be used alone or in combination. In an embodiment, the aldehyde deprotecting agent is aqueous HC1.

[0036] Step 3 is the condensation of the resulting triarylamine dialdehyde formed in Step 2 with a dialkylmalonate to form a triarylamine tetraester. This condensation reaction may be a Knoevenagel condensation type reaction. This condensation reaction may be performed in the presence of heat, catalyst and a solvent. Typical catalysts include organic bases such as piperdine, organic acids such as acetic acid, 1 : 1 mixtures of organic bases and organic acids, and Lewis acids. Those skilled in the art will understand that the catalysts exemplified above may be used alone or in combination. In an embodiment, the catalyst is piperdine. The dialkylmalonate is a dialkylmalonate that can participate in a Knoevenagel condensation reaction and form a triarylamine tetraester. Examples of useful dialkylmalonates include but are not limited to dimethylmalonate, diethylmalonate, dipropylmalonate and dibutylmalonate. In an embodiment, the dialkylmalonate is diethylmalonate.

[0037] The solvent used is a solvent suitable for Knoevenagel reactions. Suitable organic solvents include, but are not limited to toluene, xylene, benzene, cyclic alkanes such as cyclohexane, acyclic alkanes such as hexane or decane, water and alcohol solvents such as ethanol, propanol and butanol. Those skilled in the art will understand that the solvents exemplified above may be used alone or in combination. If an organic solvent is chosen, the water byproduct may be removed during the reaction. Suitable means of removing water include, but are not limited to molecular sieves and Dean-Stark trap. In an embodiment, the solvent is cyclohexane and the means of removing water is a Dean-Stark trap.

[0038] Step 4 is the reduction of the resulting triarylamine tetraester formed in Step 3 to form a triarylamine tetraol. The reduction may be performed using a reagent that reduces esters and α,β-unsaturated carbonyls to primary alcohols. The reduction may be performed in the presence of a reducing agent and a solvent. The reduction may also include a dialkylamine. Suitable reducing agents include, but are not limited to LiALH₄, DIBAL, LiBH₄, LiCl/NaBH₄, and NaBH₄in the presence of a Lewis acid. Suitable Lewis acids include, but are not limited to CoCl₂, CaCl₂, CuCl₂ and ZnCl₂. Those skilled in the art will understand that the reducing agents and Lewis acids exemplified above may be used alone or in combination. Suitable dialkylamines include diethylamine, dipropylamine and diisopropylamine. In an example, the reducing agent is NaBH₄, the Lewis acid is CoCl₂ and the dialkylamine is diisopropylamine.

[0039] The solvent used in the reduction reaction described in Step 4 is a solvent suitable for an ester α,β-unsaturated carbonyls reduction. Choice of a solvent or mixture of solvents may depend upon the reducing agents chosen for the reduction reaction. Suitable solvents include, but are not limited to ethanol, THF, diethyl ether, dichloromethane, toluene or water. Those skilled in the art will understand that the solvents exemplified above may be used alone or in combination. In an embodiment, the solvent is a mixture of THF and ethanol.

[0040] Step 5 is acrylation of the resulting triarylamine tetraol formed in Step 4 to form a triarylamine tetraacrylate. The acrylation step introduces cross linking functionality into the resulting triarylamine tetraacrylate. This acrylation is a reaction method resulting in the formation of an acrylate from a primary alcohol. A method of acrylation may involve the reaction of a primary alcohol with acryloyl chloride in the presence of solvent and a base, although other acrylation methods may be used. Useful organic solvents include, but are not limited to cyclic ethers such as tetrahydrofuran (THF) or methyl tetrahydrofuran, ethers such as diethyl ether or fert-butyl methyl ether, halogenated solvents such as dichloromethane, aromatic solvents such as toluene or xylene, acetate solvents such as ethyl acetate or butyl acetate, aliphatic solvents such as hexane or decane, and amide solvents such as dimethyl formamide (DMF), dimethyl acetamide (DMAc) and N-methylpyrrolidone (NMP). Those skilled in the art will understand that the solvents listed above may be used alone or in combination. In an embodiment, the solvent is DMF. The base used in Step 5 is a base capable of activating the primary alcohol, leading to formation of the acrylate bond. Useful bases include, but are not limited to triethylamine, tripropyl amine, piperdine, dimethylamino pyridine (DMAP) and pyridine. In an embodiment, the base is triethylamine.

[0041] Synthesis of a Novel Crosslinkable Hole Transport Molecule Having Four Radical

Polymerizable Groups

[0042] Buchwald-Hartwig Reaction

[0043] An oven dried 2 L 3 -neck round bottom flask equipped with a Teflon-coated magnetic stirrer and a reflux condenser was charged with anhydrous toluene (600 mL), /?ara-toluidine (30.10 g, 281 mmol), 4-bromobenzaldehyde dimethyl acetal (136.8 g, 592 mmol), sodium tert- butoxide (69.67 g, 725 mmol), tris(dibenzylideneacetone) dipalladium(O) (1.00 g, 1.09 mmol) and tri-tert-butylphosphonium tetrafluorob orate (0.660 g, 2.27 mmol). The resulting slurry was heated to reflux for 18 h. The material was cooled to room temperature and filtered. Solvent was removed under vacuum to yield the following triarylamine compound 1 :

[0044] Aldehyde Deprotection

[0045] Aqueous HC1 was added to triarylamine compound 1 with vigorous stirring to yield a dull yellow solid. This material was filtered, washed with water and dried under vacuum to yield 86.0 g of the following triarylamine dialdehyde compound 2:

2

[0046] Condensation

[0047] An oven dried 250 mL 4-neck round bottom flask equipped with a Teflon-coated magnetic stirrer and a Dean-Stark trap was charged with cyclohexane (120 mL) triarylamine dialdehyde compound 2 (12.0 g, 38 mmol), diethyl malonate (15.24 g, 95 mmol), and piperidine (1.62 g, 19 mmol). The resulting solution was heated to reflux for 18 h. The resulting material was cooled to room temperature and solvent was removed under vacuum. The resulting oil was triturated with hexane (50 mL). The resulting yellow solid was washed with hexane (2 X 50 mL) and dried in an oven at 60°C to yield 18.0 g of the following triarylamine tetraester compound 3:

3

[0048] Reduction

[0049] A 1 L jacketed reaction vessel was equipped with a mechanical stirrer and a condenser was charged with THF (150 mL), triarylamine tetraester compound 3 (20.0 g, 33 mmol), anhydrous ethanol, cobalt (II) chloride hexahydrate (1.59 g, 6.7 mmol) and di-isopropylamine (1.87 mL, 13 mmol). The material was cooled to 15°C and sodium borohydride (27.7 g, 732 mmol) was added slowly over 1 h. 90 Minutes after the addition was complete, the jacket temperature was raised to 20°C and the resulting mixture was stirred for 18 hours. The reaction was quenched with water (200 mL), then by aqueous ammonium chloride. The mixture was filtered and the solids were washed with water (1 L). The resulting aqueous layer was extracted with ethyl acetate. The organic layer was washed with aqueous HC1, aqueous KOH, brine and dried over MgSC Solvent was removed under vacuum to yield 13.2 g of the following triarylamine tetraol compound 4:

4

[0050] Acrylation

[0051] A I L 3-neck flask was equipped with a Teflon-coated magnetic stirrer and a dropping funnel was charged with triarylamine tetraol compound 4 (10.5 g, 24.1 mmol) and triethylamine (26.8 mL, 19.5 g, 193 mmol). Acryloyl chloride (19.5 mL, 21.7 g, 240 mmol) was added to the dropping funnel and then added to the mixture over 20 min. The material was stirred at room temperature for 20 h. The reaction was then quenched with aqueous sodium hydroxide and the material was transferred to a separately funnel containing 400 mL of ethyl acetate. The ethyl acetate solution was washed with aqueous sodium hydroxide, water, saturated NaHCC , brine and dried over MgSC Solvent was removed under vacuum and the resulting yellow oil was purified by flash chromatography. Removal of solvent provided the novel triarylamine tetraacrylate compound 5. Triarylamine tetraacrylate compound 5 was then used as the crosslinkable hole transport molecule in an overcoat layer for use in a photoconductor.

[0052] Preparation of a Photoconductor Drum Using Crosslinkable Hole Transport Molecule Having Four Radical Polymerizable Groups

[0053] A photoconductor drum to be used in a color printer was formed using an aluminum substrate, a charge generation layer coated onto the aluminum substrate, and a charge transport layer coated on top of the charge generation layer.

[0054] The charge generation layer was prepared from a dispersion including type IV titanyl phthalocyanine, type I titanylphthalocyanine, polyvinylbutyral, poly(methyl-phenyl)siloxane and polyhydroxystyrene at a weight ratio of 41 :21 :34: 1.3 :2.5 in a mixture of 2-butanone and cyclohexanone solvents. The polyvinylbutyral is available from Sekisui Chemical Co., Ltd under the trade name BX-1®. The charge generation dispersion was coated onto the aluminum substrate through dip coating and dried at 100°C for 15 minutes to form the charge generation layer having a thickness of less than 1 μπι, specifically a thickness of about 0.2 μπι to about 0.3 μπι.

[0055] The charge transport layer was prepared from a formulation including terphenyl diamine derivatives and polycarbonate at a weight ratio of 33 :67 in a mixed solvent of THF and 1,4- dioxane. The charge transport formulation was coated on top of the charge generation layer and cured at 120°C for 1 hour to form the charge transport layer having a thickness of about 30 μπι as measured by an eddy current tester. [0056] An overcoat layer was then prepared from a formulation including the following: 25g the crosslinkable hole transport molecule containing four radical polymerizable functional groups shown below:

and 25g of a crosslinkable urethane acrylate binder having 6 functional groups (available under the tradename EBECRYL® 8301), 100 g of ethanol, and 0.03 g of a coating additive (available under the tradename CoatOsil ®3509). The formulation was coated through dip coating on the outer surface of the above described photoconductor drum. The coated layer was then exposed to an electron beam source at an accelerating voltage of 90 kV, a current of 3 mA, and an exposure time of 1.2 seconds. The electron beam cured photoreceptor was then thermally cured at 120°C for 1 hour. The thickness of the overcoat was determined by eddy current measurement. The resulting photoconductor is referred to as Photoconductor Drum # 1.

[0057] Photoconductor Drum #2 was prepared the same way as outlined in the preparation of Photoconductor Drum #1 above, except the coated photoconductor was exposed to an electron beam source at an accelerating voltage of 110 kV, a current of 3 mA, and an exposure time of 1.2 seconds.

[0058] Example Comparative Photoconductor Drum

[0059] An overcoat layer was prepared from a formulation including a crosslinkable hole transport molecule containing two radical polymerizable functional groups (25 g) shown below:

and EBECRYL 8301 (20 g), ethanol (100 g) and CoatOsil 3509 (0.03 g). The formulation was coated through dip coating on the outer surface of the above described photoconductor drum. The coated layer was then exposed to an electron beam source at an accelerating voltage of 90 kV, a current of 3 raA, and an exposure time of 1.2 seconds. The electron beam cured photoreceptor was then thermally cured at 120°C for 1 h. The resulting photoconductor is referred to as Comparative Color Photoconductor Drum.

[0060] Testing Results

[0061] Photoconductor Drum #1 and Comparative Photoconductor Drum were analyzed on an in-house electrostatic tester. Both photoconductor drums were charged to -650 V and exposed to a 780 nm light source of variable energy. The voltage versus exposure energy curves are shown in Figure 1. These curves show that the initial electrical properties of Photoconductor Drum #1 were very similar to that for the Comparative Photoconductor Drum. Therefore there was no compromising of the photoconductor' s electrical properties by including the novel hole transport molecule of the present invention.

[0062] Photoconductor Drums #1 and #2, and Comparative Photoconductor Drum were installed in a Lexmark C780 Color Laser Printer. The printer was run in a 50 ppm, 2 page/pause, simplex run mode until overcoat wear thru as determined by periodic eddy current

measurements. Table 1 summarizes the initial overcoat thickness, and overcoat life as expressed in 1000 (k) prints.

Table 1

[0063] Table 1 describes the abrasion resistance of Photoconductor Drums #1 and #2 that included the novel hole transport molecule of the present invention versus Example Comparative Photoconductor Drum having a prior art hole transport molecule. The printing platform is a Lexmark C780 color laser printer that uses an intermediate transfer member (ITM). In this configuration, the photoconductor drum deposits the toned image to an ITM, which in turn transfers the image to paper. The wear in printers utilizing an ITM is very uniform from top-to- bottom of the photoconductor drum in this configuration. The data shows a dramatic increase in print count from the photoconductor drum of Photoconductor Drums #1 versus Example

Comparative Photoconductor Drum. Photoconductor Drums #2 shows that an even greater increase in print count is achieved by increasing the electron beam energy from 90 kV to 1 10 kV.

[0064] The foregoing description illustrates various aspects of the present disclosure. It is not intended to be exhaustive. Rather, it is chosen to illustrate the principles of the present disclosure and its practical application to enable one of ordinary skill in the art to utilize the present disclosure, including its various modifications that naturally follow. All modifications and variations are contemplated within the scope of the present disclosure as determined by the appended claims. Relatively apparent modifications include combining one or more features of various embodiments with features of other embodiments.

What is claimed is:

Claims

1. A crosslinkable hole transport molecule having four radical polymerizable functional groups having the following general structure:

unsubstituted arylalkyl, wherein the alkyl portion of the arylalkyl can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted , (v) an alkylaryl group, which can be substituted or unsubstituted alkylaryl, wherein the alkyl portion of the alkylaryl can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted, (vi) an alkoxy group, (vii) an aryloxy group, which can be substituted or unsubstituted aryloxy, (viii) an arylalkyloxy group, which can be substituted or unsubstituted arylalkyloxy, wherein the alkyl portion of the arylalkyloxy can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted, and (ix) an alkylaryloxy group, which can be substituted or unsubstituted alkylaryloxy, wherein the alkyl portion of the alkylaryloxy can be linear or branched, saturated or unsaturated, cyclic or acyclic, and substituted or unsubstituted.

2. The crosslinkable hole transport molecule having four radical polymerizable functional groups of claim 1 wherein the radical polymerizable group R¹ is selected from the group consisting of an acrylate group, a methacrylate group, an allylic group, a glycidyl, an ether group and an epoxy group.

3. The crosslinkable hole transport molecule having four radical polymerizable functional groups of claim 2 wherein the radical polymerizable group R¹ is an acrylate group.

4. The crosslinkable hole transport molecule having four radical polymerizable functional groups of claim 1 wherein R² and R⁴ are hydrogen.

5. The crosslinkable hole transport molecule having four radical polymerizable functional groups of claim 1 wherein R³ is a methyl group.

6. A crosslinkable hole transport molecule having four radical polymerizable functional groups having the following structure:

wherein R^l is an acrylate group, R² and R⁴ are hydrogen, and R³ is a methyl group.