Photoinitiators, compositions, and methods of forming objects

Abstract

A photoconvertible photoinitiator comprising a photochromic molecule comprising one or more substituents wherein at least one substituent comprises a substituted or unsubstituted alpha-diketone moiety represented by the general formula Ar1-C (= O)-C (= O)-Ar2 wherein Ar1 and Ar2 are the same or different and are independently a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group. Preferably, the photochromic molecule comprises a benzo spiropyran molecule, a naphthopyran molecule, or a spironaphthoxazine molecule. Also disclosed are photocurable compositions, curable resin compositions, and methods of forming an object, wherein the photocurable compositions, curable resin compositions, and methods include the photoconvertible photoinitiators described herein.

Description

[0001] Priority claim

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 450,936, filed on March 8, 2023, the entire contents of which are incorporated herein by reference for all purposes. Technical Field

[0003] The present invention relates to the technical field of three-dimensional printing and related compositions, materials, methods and products. Summary of the invention

[0004] The present invention comprises photoconvertible photoinitiators, photohardenable compositions, hardenable resin compositions, and methods of forming objects, wherein the photohardenable compositions, hardenable resin compositions, and methods comprise the photoconvertible photoinitiators described herein.

[0005] According to one aspect of the present invention, a photo-switchable photoinitiator is provided, which comprises a photochromic molecule, wherein the photochromic molecule comprises one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone portion, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule, or a spironaphthooxazine molecule, and wherein the substituted or unsubstituted α-diketone portion is represented by the general formula (I):

[0006] Ar 1 -C(=O)-C(=O)-Ar 2

[0007] (I)

[0008] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

[0009] According to another aspect of the present invention, there is provided a photohardenable composition comprising a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator can be activated by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photochromic molecule, wherein the photochromic molecule comprises one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone portion, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule or a spironaphthooxazine molecule, and wherein the substituted or unsubstituted α-diketone portion is represented by the general formula (I):

[0010] Ar 1-C(=O)-C(=O)-Ar 2

[0011] (I)

[0012] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

[0013] It may be desirable for the photohardenable composition to exhibit non-Newtonian rheological behavior.

[0014] According to another aspect of the present invention, there is provided a hardenable resin composition that can be used to form an object, the composition comprising: (i) a photohardenable composition; and (ii) a resin component that can be hardened by a heat-driven reaction or mechanism, the resin component comprising a monomer, an oligomer, a prepolymer, a polymer, or a mixture comprising at least one of the foregoing, wherein the photohardenable composition comprises a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator can be activated by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photochromic molecule, the photochromic molecule comprises one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule, or a spironaphthooxazine molecule, and wherein the substituted or unsubstituted α-diketone moiety is represented by the general formula (I):

[0015] Ar 1 -C(=O)-C(=O)-Ar 2

[0016] (I)

[0017] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

[0018] It may be desirable for a photohardenable composition to exhibit non-Newtonian rheological behavior to be included in the hardenable resin according to the present invention.

[0019] It may be desirable for the hardenable resin to exhibit non-Newtonian rheological behavior.

[0020] According to another aspect of the present invention, there is provided a method of forming an object, the method comprising:

[0021] (a) providing a volume containing a photohardenable composition, wherein the photohardenable composition comprises a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator is activatable by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photochromic molecule, the photochromic molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule, or a spironaphthooxazine molecule, and wherein the substituted or unsubstituted α-diketone moiety is represented by the general formula (I):

[0022] Ar 1 -C(=O)-C(=O)-Ar 2

[0023] (I)

[0024] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl;

[0025] (b) irradiating one or more selected locations within the volume of the photohardenable composition with light having a first wavelength and light having a second wavelength simultaneously or sequentially, wherein the light having the first wavelength and the light having the second wavelength activate the photoconvertible photoinitiator at the one or more selected locations to induce a crosslinking or polymerization reaction in the photohardenable composition at the intersection of the first and second wavelengths at the one or more selected locations within the volume to at least partially form an object; and

[0026] (c) optionally repeating step b) irradiating the photohardenable composition at one or more of the same or different selected locations in the volume until the object is partially or completely formed.

[0027] It may be desirable for photohardenable compositions to exhibit non-Newtonian rheological behavior in order to be included in the methods according to the present invention.

[0028] According to another aspect of the present invention, there is provided a method of forming an object, comprising:

[0029] (a) providing a volume of a hardenable resin composition, wherein the hardenable resin composition comprises (i) a photohardenable composition; and (ii) a resin component that is hardenable by a heat-driven reaction or mechanism, the resin component comprising a monomer, an oligomer, a prepolymer, a polymer, or a mixture comprising at least one of the foregoing, wherein the photohardenable composition comprises a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator is activatable by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photochromic molecule, the photochromic molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule, or a spironaphthooxazine molecule, and wherein the substituted or unsubstituted α-diketone moiety is represented by the general formula (I):

[0030] Ar 1 -C(=O)-C(=O)-Ar 2

[0031] (I)

[0032] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl;

[0033] (b) forming an intermediate object from the hardenable resin composition, wherein the forming of the intermediate object comprises:

[0034] (i) irradiating one or more selected locations within the volume of the hardenable resin composition with light having a first wavelength and light having a second wavelength simultaneously or sequentially, wherein the light having the first wavelength and the light having the second wavelength activate the photo-switchable photoinitiator at the one or more selected locations to induce a crosslinking or polymerization reaction in the photohardenable composition at the intersection of the first and second wavelengths at the one or more selected locations within the volume to at least partially form an object; and

[0035] (ii) optionally repeating step (i) at one or more of the same or different selected locations within the volume of the hardenable resin composition until an intermediate object is formed; and

[0036] (c) hardening (e.g., further reacting, further polymerizing, further chain extending) the resin components in the intermediate object through a heat-driven reaction or mechanism to form the object.

[0037] It may be desirable for photohardenable compositions to exhibit non-Newtonian rheological behavior in order to be included in the methods according to the present invention.

[0038] It may be desirable for the hardenable resin composition to exhibit non-Newtonian rheological behavior in order to be included in the method according to the present invention.

[0039] It should be understood by those skilled in the art to which the present invention relates that any feature described herein with respect to any specific aspect and / or embodiment of the present invention may be combined with any other feature of any other aspect and / or embodiment of the present invention described herein or more, and appropriate modifications are made to ensure the compatibility of the combination. Such combinations are considered to be part of the present invention contemplated by the present disclosure.

[0040] The foregoing as well as other aspects and embodiments described herein and contemplated by this disclosure all constitute embodiments of the present invention.

[0041] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

[0042] Other embodiments will be apparent to those skilled in the art from consideration of the specification, claims, and practice of the invention disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0044] Various aspects and embodiments of the invention are further described in the following detailed description.

[0045] The present invention includes a photoconvertible photoinitiator comprising a photochromic molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety as described herein, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule, or a spironaphthooxazine molecule. The present invention also includes a photohardenable composition, a hardenable resin composition, and a method of forming an object, the photohardenable composition, the hardenable resin composition, and the method comprising the photoconvertible photoinitiator as described herein.

[0046] The photo-switchable photoinitiator described herein preferably has photochromic properties and can be converted into a second form (or activated form) when irradiated with light of a first wavelength, and the second form can be converted into an excited state when irradiated with light of a second wavelength, and the second state can induce photopolymerization or photocrosslinking reaction.

[0047] While not wishing to be bound by theory, it is believed that the inclusion of substituents comprising a substituted or unsubstituted α-diketone moiety as described herein can advantageously expand the range of spectra over which the photoswitchable photoinitiator can be excited and can also enhance the photoinitiation ability of the photoswitchable photoinitiator.

[0048] According to one aspect of the present invention, a photo-switchable photoinitiator is provided, which comprises a photochromic molecule, wherein the photochromic molecule comprises one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone portion, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule, or a spironaphthooxazine molecule, and wherein the substituted or unsubstituted α-diketone portion is represented by the general formula (I):

[0049] Ar 1 -C(=O)-C(=O)-Ar 2

[0050] (I)

[0051] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

[0052] The α-diketone moiety may be attached to the photochromic molecule directly or indirectly, preferably via a single carbon-carbon bond.

[0053] The aryl group includes substituents or functional groups derived from an aromatic ring, including but not limited to a benzene ring, a naphthalene ring, an anthracene ring, an indene ring, a fluorene ring, etc. The aryl group may be substituted or unsubstituted.

[0054] The heteroaryl group includes a substituent or functional group derived from a heteroaryl ring, including but not limited to a furan ring, a thiophene ring, a pyrrole ring, an oxazole ring, an isoxazole ring, a thiazole ring, an isothiazole ring, an imidazole ring, a pyrazole ring, a pyran ring, a pyridine ring, a pyrazine ring, an indole ring, a quinoline ring, an isoquinoline ring, a xanthene ring, a carbazole ring, an acridine ring, an indoline ring, a julolidine ring, etc. The heteroaryl group may be substituted or unsubstituted.

[0055] Of those mentioned above, Ar 1 and Ar 2 One or both may preferably contain a phenyl group.

[0056] Examples of substituents that may replace the hydrogen atom attached to the aryl or heteroaryl group in the substituted aryl or heteroaryl group include, but are not limited to, halogen atoms, alkyl groups, alkoxy groups, alkylamino groups, dialkylamino groups, alkylthio groups, heterocyclic groups, and more specifically, methyl groups, ethyl groups, isopropyl groups, tert-butyl groups, phenyl groups, trifluoromethyl groups, cyano groups, acetyl groups, ethoxycarbonyl groups, carboxyl groups, carboxyl groups, amino groups, methylamino groups, dimethylamino groups, ethylamino groups, diethylamino groups, isopropylamino groups, diisopropylamino groups, cyclohexylamino groups, dicyclohexylamino groups, acetylamino groups, piperidinyl groups, pyrrolidinyl groups, --PO3 groups, H, methoxy, ethoxy, propoxy, isopropoxy, butoxy, pentyloxy, phenoxy, hydroxyl, acetoxy, methylthio, ethylthio, isopropylthio, mercapto, acetylthio, thiocyano, methylsulfinyl, methylsulfonyl, dimesylsulfonyl, sulfonate or salt group, fluorine atom, chlorine atom, bromine atom, iodine atom, trimethylsilyl, triethylsilyl, furyl, thienyl, pyridyl, piperidyl, morpholino, pyrrolidinyl and the like.

[0057] Specific examples of the α-diketone moiety represented by formula (I) include, but are not limited to, the following compounds represented by formula (IA)-(IK):

[0058]

[0059]

[0060] Optionally, Ar in the general formula (I) 1 and / or Ar 2 And any compound represented by Formula (IA)-(IK) may contain one or more substituents on one or both of the aryl or heteroaryl groups, which substituents may be the same or different. Examples of substituents include, but are not limited to, hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted cycloalkenyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aryl, substituted or unsubstituted aralkyl, substituted or unsubstituted alkylaryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted aryloxy, substituted or unsubstituted alkoxy, substituted or unsubstituted ester, substituted or unsubstituted carbonate, substituted or unsubstituted keto, substituted or unsubstituted aldehyde, substituted or unsubstituted imino, substituted or unsubstituted carboxyl, substituted or unsubstituted amide, substituted or unsubstituted carbamate, substituted or unsubstituted urea, substituted or unsubstituted tetrazine, substituted or unsubstituted amino, iodo, bromo, chloro, fluoro, cyano, nitro, hydroxyl, thiol, alkyl thioether, aryl thioether, substituted or unsubstituted alcohol, and those listed above.

[0061] As described above, the photochromic molecule may comprise a benzospiropyran molecule containing one or more substituents.

[0062] The photoconvertible photoinitiator comprising a benzospiropyran molecule described herein preferably has photochromic properties and can be converted to a second form (or activated form) when irradiated with light of a first wavelength, and the second form can be converted to an excited state when irradiated with light of a second wavelength, and the second state can induce crosslinking or photopolymerization of the photohardenable composition. The conversion (conversion) of the photoconvertible photoinitiator described herein to the second form of the molecule (e.g., its isomer, for example, for a photochromic molecule having a closed ring structure, to a second form as its open ring form) is preferably a reversible photochemical structural change. The preferred photoconvertible photoinitiator according to the present invention undergoes a reversible intramolecular deformation (transformation) by irradiation (photochromism) to form a merocyanine isomer (MC). This preferred photoconvertible photoinitiator can function to form a merocyanine isomer (activated form) by light-activated opening of the benzospiropyran (BSP) ring. The activated form can then absorb light of a different wavelength to form an excited state of the activated form, which can then induce photoinitiation. This preferred photo-switchable photoinitiator can also undergo a reversible intramolecular transformation upon heating to form a MC.

[0063] Preferred benzospiropyran photochromic molecules include benzospiropyran molecules represented by general formula (II):

[0064]

[0065] Where R 1 -R 13 are the same or different, and independently represent, for example, hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkylaryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted ester group, a substituted or unsubstituted carbonate or salt group, a substituted or unsubstituted keto group, a substituted or unsubstituted aldehyde group, a substituted or unsubstituted imino group, a substituted or unsubstituted carboxyl group, a substituted or unsubstituted amide group, a substituted or unsubstituted carbamate group, a substituted or unsubstituted urea group, a substituted or unsubstituted tetrazine group, a substituted or unsubstituted amino group, an iodine group, a bromine group, a chlorine group, a fluorine group, a cyano group, a nitro group, a hydroxyl group, a thiol group, an alkyl thioether group, an aryl thioether group, or a substituted or unsubstituted alcohol group, and

[0066] Where R 1 -R 13 At least one of them contains a substituted or unsubstituted α-diketone moiety represented by the general formula (I):

[0067] Ar 1 -C(=O)-C(=O)-Ar2

[0068] (I)

[0069] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

[0070] The α-diketone moiety may be attached to the photochromic molecule directly or indirectly, preferably via a single carbon-carbon bond.

[0071] For example, a substituted or unsubstituted α-diketone moiety may serve as R 1 To R 13 at least one of which is directly connected to the ring of the benzospiropyran molecule by a bond or which may be indirectly connected to the ring of the benzospiropyran molecule by connection to a substituent or moiety, which serves as R 1 To R 13 One of them is connected to the ring of the benzospiropyran molecule.

[0072] Optionally, any two adjacent R 1 To R 13 The group may contain the atoms necessary to complete the ring structure linking two adjacent groups together, in which case one or more substituted or unsubstituted α-diketone moieties may be attached to the ring structure.

[0073] Examples of substituted or unsubstituted α-diketone moieties for inclusion in the substituents on the photochromic molecule comprising a benzospiropyran molecule include, but are not limited to, those discussed above.

[0074] The photo-switchable photoinitiator described herein comprises a benzospiropyran molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety represented by the general formula (I), which can be prepared using known synthetic techniques. As an example, but not limited to, the substituted or unsubstituted α-diketone moiety represented by the general formula (I) can be used as a substituent to be connected to a bromo- or iodo-substituted benzospiropyran molecule by, for example, a palladium-catalyzed cross-coupling reaction, with high yield, mild conditions, and synthetic versatility.

[0075] As described above, the photochromic molecule may comprise a naphthopyran molecule having one or more substituents.

[0076] The photoconvertible photoinitiator described herein, which contains a photochromic molecule containing a naphthopyran molecule, preferably has a photochromic property and can be converted into a second form (or activated form) when irradiated with light of a first wavelength, and the second form can be converted into an excited state when irradiated with light of a second wavelength, and the second state can induce the hardening of the photohardenable resin component. The conversion (conversion) of the photoconvertible photoinitiator described herein to the second form of the molecule (e.g., its isomer, for example, for a photochromic molecule with a closed ring structure, to a second form as its open ring form) is preferably a reversible photochemical structural change. The preferred photoconvertible photoinitiator according to the present invention undergoes a reversible intramolecular deformation (transformation) by irradiation (photochromism) to form an open isomeric form (activated form). This preferred photoconvertible photoinitiator can function to form an open isomeric form (activated form) by opening the naphthopyran ring with light activation. The activated form can then absorb light of different wavelengths to form an excited state of the activated form, which can then induce photoinitiation. This preferred photo-switchable photoinitiator can also undergo a reversible intramolecular transformation upon heating to form an open isomeric form.

[0077] Examples of the photochromic molecules comprising naphthopyran molecules for inclusion in the photo-switchable photoinitiator according to the present invention include those represented by the general formula (III):

[0078]

[0079] Where R a , R b and R 1 -R 8 are the same or different, and represent, for example, hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkylaryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted ester group, a substituted or unsubstituted carbonate group, a substituted or unsubstituted keto group, a substituted or unsubstituted aldehyde group, a substituted or unsubstituted imino group, a substituted or unsubstituted carboxyl group, a substituted or unsubstituted amide group, a substituted or unsubstituted carbamate group, a substituted or unsubstituted urea group, a substituted or unsubstituted tetrazine group, a substituted or unsubstituted amino group, an iodine group, a bromine group, a chlorine group, a fluorine group, a cyano group, a nitro group, a hydroxyl group, a thiol group, an alkyl thioether group, an aryl thioether group, or a substituted or unsubstituted alcohol group, and

[0080] Where R a , R b and R 1 -R 8At least one of the compounds comprises a substituted or unsubstituted α-diketone moiety represented by the general formula (I):

[0081] Ar 1 -C(=O)-C(=O)-Ar 2

[0082] (I)

[0083] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

[0084] As mentioned above, the α-diketone moiety may be attached to the photochromic molecule directly or indirectly, preferably via a single carbon-carbon bond.

[0085] For example, a substituted or unsubstituted α-diketone moiety may serve as R a , R b and R 1 -R 8 at least one of which is directly connected to the ring of the naphthopyran molecule by a bond or which may be indirectly connected to the ring of the naphthopyran molecule through a bond to a substituent or moiety which is R a , R b and R 1 -R 8 One of them is connected to the ring of the naphthopyran molecule.

[0086] Optionally, any two adjacent R a , R b and R 1 -R 8 The group may contain the atoms necessary to complete the ring structure linking two adjacent groups together, in which case one or more substituted or unsubstituted α-diketone moieties may be attached to the ring structure.

[0087] Preferably R a and R b At least one or both of R and R contain aryl or heteroaryl groups, which may be substituted or unsubstituted. a and R b At least one or both of R comprises a substituted or unsubstituted α-diketone moiety attached thereto. More preferably, R a and R b Each may comprise a phenyl group, wherein each phenyl group has a substituted or unsubstituted α-diketone moiety attached thereto.

[0088] Examples of the photo-switchable photoinitiator according to the present invention comprising a naphthopyran molecule represented by the general formula (III) include those represented by the following formula (III-A):

[0089]

[0090] Unless otherwise indicated, in the formulae contained herein, when a substituent may be indicated at one or more positions but not all positions, the position where a specific substituent is not indicated is occupied by hydrogen.

[0091] Examples of the photochromic molecules comprising naphthopyran molecules for inclusion in the photo-switchable photoinitiator according to the present invention also include those represented by the general formula (IV):

[0092]

[0093] Where R a , R b and R 1 -R 8 are the same or different, and represent, for example, hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkylaryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted ester group, a substituted or unsubstituted carbonate group, a substituted or unsubstituted keto group, a substituted or unsubstituted aldehyde group, a substituted or unsubstituted imino group, a substituted or unsubstituted carboxyl group, a substituted or unsubstituted amide group, a substituted or unsubstituted carbamate group, a substituted or unsubstituted urea group, a substituted or unsubstituted tetrazine group, a substituted or unsubstituted amino group, an iodine group, a bromine group, a chlorine group, a fluorine group, a cyano group, a nitro group, a hydroxyl group, a thiol group, an alkyl thioether group, an aryl thioether group, or a substituted or unsubstituted alcohol group, and

[0094] Where R a , R b and R 1 -R 8 At least one of them contains a substituted or unsubstituted α-diketone moiety represented by the general formula (I):

[0095] Ar 1 -C(=O)-C(=O)-Ar 2

[0096] (I)

[0097] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

[0098] As mentioned above, the α-diketone moiety may be attached to the photochromic molecule directly or indirectly, preferably via a single carbon-carbon bond.

[0099] For example, a substituted or unsubstituted α-diketone moiety may serve as R a , R b and R 1 -R 8 at least one of which is directly connected to the ring of the naphthopyran molecule by a bond or which may be indirectly connected to the ring of the naphthopyran molecule through a bond to a substituent or moiety which is R a , R b and R 1 -R 8 One of them is connected to the ring of the naphthopyran molecule.

[0100] Optionally, any two adjacent R a , R b and R 1 -R 8 The group may contain the atoms necessary to complete the ring structure linking two adjacent groups together, in which case one or more substituted or unsubstituted α-diketone moieties may be attached to the ring structure.

[0101] Preferably R a and R b At least one or both of R and R contain aryl or heteroaryl groups, which may be substituted or unsubstituted. a and R b At least one or both of R comprises a substituted or unsubstituted α-diketone moiety attached thereto. More preferably, R a and R b Each may comprise a phenyl group, wherein each phenyl group has a substituted or unsubstituted α-diketone moiety attached thereto.

[0102] The photoconvertible photoinitiator described herein comprises a naphthopyran molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety represented by the general formula (I), which can be prepared using known synthetic techniques. As an example, but not limited to, the substituted or unsubstituted α-diketone moiety described herein can be connected as a substituent to a bromo- or iodo-substituted naphthopyran molecule by, for example, a palladium-catalyzed cross-coupling reaction, with high yield, mild conditions, and synthetic versatility.

[0103] As described above, the photoswitchable photoinitiators described herein may include photochromic molecules including substituted or unsubstituted spironaphthoxazine molecules.

[0104] The photoconvertible photoinitiator described herein, comprising a photochromic molecule containing a spironaphthooxazine molecule, preferably has photochromic properties and is convertible to a second form (or activated form) when irradiated with light of a first wavelength, the second form being convertible to an excited state when irradiated with light of a second wavelength, the second state being capable of inducing the hardening of a photohardenable resin component. The conversion of the photoconvertible photoinitiator described herein to the second form of the molecule (e.g., an isomer thereof, e.g., for a photochromic molecule having a closed ring structure, to a second form that is an open ring form thereof) is preferably a reversible photochemical structural change. The preferred photoconvertible photoinitiator according to the present invention undergoes a reversible intramolecular deformation (transformation) by irradiation (photochromism) to form an open isomeric form (activated form). This preferred photoconvertible photoinitiator can function to form an open isomeric form (activated form) by photoactivated opening of the spironaphthooxazine ring. The activated form can subsequently absorb light of a different wavelength to form an excited state of the activated form, which can then induce photoinitiation. This preferred photo-switchable photoinitiator can also undergo a reversible intramolecular transformation upon heating to form an open isomeric form.

[0105] Examples of photochromic molecules comprising spironaphthoxazine molecules for inclusion in the photo-switchable photoinitiator according to the present invention also include those represented by general formula (V):

[0106]

[0107] Where R 1 -R 14 are the same or different, and represent, for example, hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkylaryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted ester group, a substituted or unsubstituted carbonate or salt group, a substituted or unsubstituted keto group, a substituted or unsubstituted aldehyde group, a substituted or unsubstituted imino group, a substituted or unsubstituted carboxyl group, a substituted or unsubstituted amide group, a substituted or unsubstituted carbamate group, a substituted or unsubstituted urea group, a substituted or unsubstituted tetrazine group, a substituted or unsubstituted amino group, an iodine group, a bromine group, a chlorine group, a fluorine group, a cyano group, a nitro group, a hydroxyl group, a thiol group, an alkyl thioether group, an aryl thioether group, or a substituted or unsubstituted alcohol group;

[0108] Where R 1 -R 14 At least one of them contains a substituted or unsubstituted α-diketone moiety represented by the general formula (I):

[0109] Ar 1-C(=O)-C(=O)-Ar 2

[0110] (I)

[0111] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

[0112] As mentioned above, the α-diketone moiety may be attached to the photochromic molecule directly or indirectly, preferably via a single carbon-carbon bond.

[0113] For example, a substituted or unsubstituted α-diketone moiety may serve as R 1 To R 14 at least one of which is directly connected to the ring of the spironaphthooxazine molecule by a bond or which may be indirectly connected to the ring of the spironaphthooxazine molecule by connection to a substituent or moiety as R 1 To R 14 One of them is connected to the ring of the spironaphthoxazine molecule.

[0114] Optionally, any two adjacent R 1 To R 14 The group may contain the atoms necessary to complete the ring structure linking two adjacent groups together, in which case one or more substituted or unsubstituted α-diketone moieties may be attached to the ring structure.

[0115] Preferably R 1 To R 14 At least one of the comprises an aryl or heteroaryl group, which may be substituted or unsubstituted. Optionally, in this case, a substituted or unsubstituted α-diketone moiety may be attached thereto.

[0116] It is desirable that R in the general formula (V) 1 Contains substituted or unsubstituted alkyl or aryl groups (eg, benzyl, ie, a benzene ring to which a CH2 group is attached).

[0117] Examples of the photo-switchable photoinitiator according to the present invention comprising the spironaphthoxazine molecule represented by the general formula (V) include those represented by the following formula (VA):

[0118]

[0119] Examples of photochromic molecules comprising spironaphthoxazine molecules for inclusion in the photo-switchable photoinitiator according to the present invention also include those represented by the general formula (VI):

[0120]

[0121] Where R 1 -R 14 are the same or different, and represent, for example, hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkylaryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted ester group, a substituted or unsubstituted carbonate or salt group, a substituted or unsubstituted keto group, a substituted or unsubstituted aldehyde group, a substituted or unsubstituted imino group, a substituted or unsubstituted carboxyl group, a substituted or unsubstituted amide group, a substituted or unsubstituted carbamate group, a substituted or unsubstituted urea group, a substituted or unsubstituted tetrazine group, a substituted or unsubstituted amino group, an iodine group, a bromine group, a chlorine group, a fluorine group, a cyano group, a nitro group, a hydroxyl group, a thiol group, an alkyl thioether group, an aryl thioether group, or a substituted or unsubstituted alcohol group;

[0122] Where R 1 -R 14 At least one of them contains a substituted or unsubstituted α-diketone moiety represented by the general formula (I):

[0123] Ar 1 -C(=O)-C(=O)-Ar 2

[0124] (I)

[0125] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

[0126] As mentioned above, the α-diketone moiety may be attached to the photochromic molecule directly or indirectly, preferably via a single carbon-carbon bond.

[0127] For example, a substituted or unsubstituted α-diketone moiety may serve as R 1 To R 14 at least one of which is directly connected to the ring of the spironaphthooxazine molecule by a bond or which may be indirectly connected to the ring of the spironaphthooxazine molecule by connection to a substituent or moiety as R 1 To R 14 One of them is connected to the ring of the spironaphthoxazine molecule.

[0128] Optionally, any two adjacent R 1 To R 14 The group may contain the atoms necessary to complete the ring structure linking two adjacent groups together, in which case one or more substituted or unsubstituted α-diketone moieties may be attached to the ring structure.

[0129] Preferably R 1 To R 14 At least one of the comprises an aryl or heteroaryl group, which may be substituted or unsubstituted. Optionally, in this case, one or more substituted or unsubstituted α-diketone moieties may be attached thereto.

[0130] It is desirable that R in the general formula (VI) 1 Contains substituted or unsubstituted alkyl or aryl groups (eg, benzyl, ie, a benzene ring to which a CH2 group is attached).

[0131] The photo-switchable photoinitiator described herein comprises a spironaphthooxazine molecule comprising one or more substituents attached thereto, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety represented by general formula (I), which can be prepared using known synthetic techniques. As an example, but not limited to, the substituted or unsubstituted α-diketone moiety described herein can be attached as a substituent to a chlorine-, bromine- or iodine-substituted spironaphthooxazine molecule by, for example, a palladium-catalyzed cross-coupling reaction, with high yield, mild conditions, and synthetic versatility.

[0132] According to another aspect of the present invention, there is provided a photohardenable composition comprising a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator can be activated by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photoconvertible photoinitiator comprising a photochromic molecule, the photochromic molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone portion, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule or a spironaphthooxazine molecule, and wherein the substituted or unsubstituted α-diketone portion is represented by the general formula (I):

[0133] Ar 1 -C(=O)-C(=O)-Ar 2

[0134] (I)

[0135] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

[0136] Preferably, the substituted or unsubstituted α-diketone moiety comprises an α-diketone moiety represented by any of the above formulae (IA) to (IK). As described above, optionally, any hydrogen attached to a ring member in any formula may alternatively comprise a substituent or moiety in its place.

[0137] As described below, photohardenable compositions that exhibit non-Newtonian rheological behavior may be desirable or preferred.

[0138] The photohardenable composition may also optionally contain a co-initiator.

[0139] The photohardenable composition may also optionally contain a sensitizer.

[0140] Optionally, the photohardenable composition may comprise a combination comprising one or more co-initiators and / or one or more sensitizers.

[0141] Several considerations when selecting a particular photoconvertible photoinitiator for inclusion in a photohardenable composition or method according to the present invention include, by way of example but not limitation, the absorption spectrum and Δmax of the molecule and its second form, the solubility of the photoconvertible photoinitiator in the photohardenable resin component, the photosensitivity of the second form of the photoconvertible photoinitiator, the amount of the initial concentration of the second form in the monomer solution, the stability of the photoconvertible photoinitiator, and the reduction potential and oxidation potential of the second form of the photoconvertible photoinitiator.

[0142] The photoconvertible photoinitiators and photohardenable compositions according to the present invention are particularly suitable for use in the methods of the present invention to form three-dimensional objects because the photoconvertible photoinitiator molecules in their closed form and the photoinitiator molecules in their activated second form (e.g., open form) have sufficiently distinct absorption spectra such that once the closed form of the molecule is converted to its open form, the open form absorbs in a wavelength region where the closed form does not substantially absorb. In this way, the open form can be independently excited by the second wavelength without causing the closed form to be undesirably excited by the second wavelength. Once the open form is produced by exposure to the first wavelength, the second wavelength can excite the open form to generate free radicals or otherwise induce a desired crosslinking or polymerization reaction in the photohardenable resin component.

[0143] The photohardenable resin component suitable for use in the photohardenable composition includes any resin (e.g., a monomer, an oligomer, a prepolymer, a polymer, or a mixture comprising at least one of the foregoing), which can be photohardened by exposure to light in the presence of a photoinitiator. Examples of photohardenable resin components that can be used for inclusion in the photohardenable composition according to the present invention include ethylenically unsaturated compounds, and more specifically, polyethylenically unsaturated compounds. These compounds include monomers having one or more ethylenically unsaturated groups, such as vinyl or allyl groups, and polymers having both terminal or side chain unsaturated olefinic bonds. Such compounds are well known in the art and include, but are not limited to, polyols, acrylates and methacrylates such as trimethylolpropane, pentaerythritol, etc.; and acrylate or methacrylate-terminated epoxy resins, acrylate or methacrylate-terminated polyesters, etc. Representative examples include, but are not limited to, ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane triacrylate (TMPTA), pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hydroxypentaacrylate (DPHPA), hexanediol-1,6-dimethacrylate, and diethylene glycol dimethacrylate. Preferred examples include, but are not limited to, urethane acrylates or urethane methacrylates.

[0144] The photohardenable resin component may optionally include one or more multifunctional acrylate monomers. Dipentaerythritol pentaacrylate, a pentafunctional acrylic monomer available from Sartomer as SR399, is an example of a photohardenable resin component that may be desirably included in the hardenable resin composition of the present invention.

[0145] It may be desirable to use an aliphatic urethane acrylate as a photohardenable resin component to be included in the hardenable resin composition described herein.

[0146] Mixtures of multifunctional acrylate monomers such as dipentaerythritol pentaacrylate (eg, SR399 from Sartomer) and aliphatic urethane acrylates may also be used.

[0147] An acrylate monomer or an acrylamide monomer may also be included in the hardenable resin composition to serve as a solvent for mixing the photoinitiator in the first resin component. An acrylate monomer may be preferred.

[0148] Preferably, the photohardenable resin component included in the photohardenable composition is selected to achieve an optionally optically transparent or clear liquid, which is desirable in processes and systems where light (eg, excitation light) is directed into the composition.

[0149] As provided herein, the photohardenable compositions according to the present invention may optionally include one or more co-initiators.

[0150] Suitable co-initiators include co-initiators that are reducing agents, oxidizing agents or hydrogen donating compounds.

[0151] Examples of useful co-initiators may be selected from those known in the art, more particularly tertiary amines and organic borates. Ionium salts may also be used, particularly in combination with borates. In certain embodiments, iodonium salts in combination with tertiary amines may also be included. Examples of other useful electron donating co-initiators are discussed in Eaton, DF, "Dye Sensitized Photopolymerization", Advances in Photochemistry, Vol. 13, pp 427-486.

[0152] Representative examples of N,N-dialkylanilines that can be used as co-initiators in the present invention include 4-cyano-N,N-dimethylaniline, 4-acetyl-N,N-dimethylaniline, 4-bromo-N,N-dimethylaniline, 4-methyl-N,N-dimethylaniline, 4-ethoxy-N,N-dimethylaniline, N,N-dimethylthioanicidine, 4-amino-N,N-dimethylaniline, 3-hydroxy-N,N-dimethylaniline, N,N,N,'N,-tetramethyl-1,4-diphenylamine, 4-acetamido-N,N-dimethylaniline, 2,6-diethyl-N,N-dimethylaniline, N,N,2,4,6-pentaneethylaniline (PMA) and p-tert-butyl-N,N-dimethylaniline.

[0153] Certain other tertiary amines are also useful co-initiators, including triethylamine, triethanolamine, N-methyldiethanolamine, 2-ethyl-4-(dimethylamino)benzoate, 2-ethylhexyl-4-(dimethylamino)benzoate, and the like.

[0154] Another class of useful co-initiators comprises alkyl borate esters (or salts), such as those of the formula BR a R b R c R d The ammonium salt of the borate anion, wherein R a -R d is independently selected from alkyl, aryl, alkaryl, allyl, aralkyl, alkenyl, alkynyl, alicyclic and saturated or unsaturated heterocyclic groups. a -R d Representative examples of alkyl groups represented by are methyl (Me), ethyl, propyl, butyl, pentyl, hexyl, octyl, stearoyl, etc. The alkyl group may be substituted, for example, with one or more halogens, cyano, acyloxy, acyl, alkoxy, or hydroxyl groups. a-R d Representative examples of the aryl group represented by include phenyl, naphthyl and substituted aryl groups such as anisyl and alkylaryl groups such as methylphenyl, dimethylphenyl and the like. a -R d Representative examples of aryl groups represented by include benzyl. Representative alicyclic groups include cyclobutyl, cyclopentyl and cyclohexyl. Examples of alkynyl groups include arylpropynyl and ethynyl, and examples of alkenyl groups include vinyl. Preferably R a , R d , R c and R d At least one but no more than three of R are alkyl groups. a , R d , R c and R d Each of may contain up to 20 carbon atoms, and they typically contain from 1 to 7 carbon atoms. More preferably R a -R d It is a combination of an alkyl group and an aryl group or an aralkyl group, and more preferably a combination of three aryl groups and one alkyl group, ie, an alkyl triphenyl borate, such as but not limited to butyl triphenyl borate.

[0155] As described herein, the photohardenable composition according to the present invention may optionally include a synergist. Non-limiting examples of synergists include amines, thiols, mercaptans, thioethers, silanes, organic borate compounds, diaryliodonium salts, triarylsulfonium salts. A preferred example of a suitable synergist is butyrylcholine butyltriphenylborate. Another preferred example of a suitable synergist is N-methyldiethanolamine. When included in a photohardenable composition, a synergist in combination with a photoconvertible photoinitiator can facilitate photoinitiation by, for example, electron transfer or hydrogen transfer in an activated form of the photoconvertible photoinitiator.

[0156] The photohardenable compositions and methods according to the present invention preferably include photohardenable compositions that exhibit non-Newtonian rheological behavior, advantageously wherein the rheological behavior can facilitate forming an object in a volume of photohardenable composition as described herein upon exposure to at least two different wavelengths of excitation light, wherein the object remains in a fixed position or is minimally displaced in a volume of unhardened photohardenable composition during formation. Minimally displaced refers to the displacement of the object being formed in the volume during its formation in an acceptable manner to accurately produce the desired part geometry.

[0157] Photohardenable compositions and methods according to the present invention may preferably include photohardenable compositions that exhibit non-Newtonian rheological behavior, which may also advantageously facilitate separation of a formed object from an unhardened photohardenable composition upon application of stress. While not wishing to be bound by theory, upon application of stress, the apparent viscosity of a non-Newtonian photohardenable composition may drop to a value (e.g., a steady shear viscosity) lower than a static value (e.g., a zero shear viscosity or a yield stress), allowing the unhardened photohardenable composition to more easily flow out and separate from an object. Examples of such non-Newtonian rheological behavior include, but are not limited to, pseudoplastic fluids, yield pseudoplasticity, Bingham plasticity, or Bingham pseudoplasticity.

[0158] By further including one or more reactive components (e.g., urethane acrylate oligomers, urethane methacrylate oligomers, acrylated or methacrylated polyurethanes, acrylated or methacrylated polyurethane-ureas, acrylated or methacrylated polyesters, acrylated or methacrylated polyamides, acrylate or methacrylate functional block copolymers, alkenyl or alkynyl functional urethane oligomers, alkenyl or Alkynyl-functional polyurethanes, alkenyl or alkynyl-functional polyurethane ureas, alkenyl or alkynyl-functional polyesters, alkenyl or alkynyl-functional polyamides, alkenyl or alkynyl-functional block copolymers, thiol-functional urethane oligomers, thiol-functional polyurethanes, thiol-functional polyurethane ureas, thiol-functional polyesters, thiol-functional polyamides, thiol-functional block copolymers) and / or by further adding one or more non-reactive additives (such as but not limited to one or more thixotropic agents and / or rheology modifiers) to the photohardenable composition, the photohardenable composition can be imparted with non-Newtonian rheological behavior. The selection of one or more reactive components and the amount thereof added to the photohardenable resin component to impart non-Newtonian rheological behavior is within the skill of those skilled in the relevant art without undue experimentation. Similarly, the selection of non-reactive additives and the amount thereof added to the photohardenable composition to impart non-Newtonian rheological behavior is within the skill of those skilled in the relevant art without undue experimentation.

[0159] For the photohardenable composition according to the present invention, preferably the steady shear viscosity is less than 30,000 centipoise, more preferably less than 10,000 centipoise, and most preferably less than 1,000 centipoise. (The steady shear viscosity refers to the viscosity after the thixotropic agent network is broken.)

[0160] filler

[0161] Optionally, the photohardenable composition according to the present invention may further comprise one or more fillers. Fillers may be included in an amount greater than 0 to about 90 weight percent, the amount being determined by the purpose of the filler and the desired end-use properties of the target three-dimensional object. Advantageously, fillers may be selected to maintain the optical clarity of the photohardenable or hardenable composition, for example, by controlling the particle size to be substantially smaller than the excitation wavelength, or by matching the refractive index of the filler and the matrix to reduce light scattering.

[0162] Fillers can be used to modify the properties of the hardened photohardenable composition, such as stiffness, strength, toughness, impact resistance, creep resistance, fatigue resistance, mechanical energy return, mechanical loss tangent, glass transition temperature, thermal degradation temperature, thermal conductivity, thermal resistance, hygroscopicity, electrical conductivity, static dissipation, dielectric constant and loss tangent, density, refractive index, light dispersion, opacity to ionizing radiation, and resistance to ionizing radiation. Fillers can also be used to modify the properties of the liquid photohardenable composition, such as rheological properties (such as viscosity and thixotropy) and optical properties (such as refractive index). Examples of fillers include, but are not limited to, silica, alumina, zirconium oxide; silicate glasses such as soda-lime glass, borosilicate glass, sodium silicate glass, lead glass, aluminosilicate glass, barium glass, thorium glass, glass ceramics; chalcogenide glass; glass microspheres and microbubbles; nanoclays such as laponite, montmorillonite, bentonite, kaolinite, hectorite, and halloysite; calcium phosphate minerals such as hydroxyapatite, mineral fillers such as chalk, rock dust, slag dust, fly ash, hydraulic cement, loess, limestone, kaolin, talc, and wollastonite. Examples of particle size ranges include, but are not limited to, less than 10 microns, less than 1 micron, 10 nm to 500 nm, 10 nm to 90 nm, 40 nm to 70 nm. Smaller particle sizes, particularly particle sizes less than about 100 nm, can be beneficial in providing high optical clarity of the liquid composition to better facilitate printing. Controlling particle size distribution, such as monodisperse, bimodal, or trimodal distribution of sizes, can be beneficial in controlling rheological properties, increasing filler weight percentage, or altering properties of the photohardenable composition.

[0163] Other additives

[0164] As mentioned above, the photohardenable composition according to the present invention may further comprise one or more additives. Examples of additives include, but are not limited to, thixotropic agents / rheology modifiers, defoamers, stabilizers, scavengers, and non-reactive solvent diluents. Any additive may be a single additive or a mixture of additives. For example, the thixotropic agent may comprise a single thixotropic agent or a mixture of two or more thixotropic agents.

[0165] The additive is preferably selected so that it does not react with the hardenable resin component, the photoinitiator, or any other additive that may be included in the photohardenable composition.

[0166] Thixotropic Agents / Rheology Modifiers

[0167] Thixotropic agents and rheology modifiers suitable for inclusion in the photohardenable compositions described herein include, for example and without limitation, urea derivatives; modified urea compounds such as Rheobyk 410 and Rheobyk-D available from BYK-Chemie GmbH (part of the ALTANA Group); 410; fumed metal oxides (also known as pyrogenic metal oxides) include, for example, but not limited to, fumed silica, fumed alumina; zirconium oxide; precipitated metal oxides include, for example, but not limited to, precipitated silica, precipitated alumina; unmodified and organically modified layered silicate clays; dimer and trimer fatty acids; polyether phosphates; oxidized polyolefins; oxidized polyolefins blended with polyamides; alkali-soluble / swellable emulsions; cellulose ethers; hydrophobically modified alkali-soluble emulsions; hydrophobically modified ethylene oxide-based urethanes; sucrose benzoate; ester-terminated polyamides; tertiary amide-terminated polyamides; polyalkylene oxide-terminated polyamides; polyether amides; acrylamidomethyl-substituted cellulose ester polymers; polyethylene imine; polyureas; organoclays; hydrogenated castor oil; organic alkali salts of clay minerals (e.g., montmorillonite) and other silicate-type materials; aluminum, calcium and zinc salts of fatty acids (e.g., lauric acid or stearic acid).

[0168] For information on urea derivatives useful as thixotropic agents, see U.S. Pat. No. 6,548,593 to Merz et al., issued April 15, 2003, and U.S. Pat. No. 9,376,602 to Walther et al., issued June 28, 2016, which are hereby incorporated by reference in their entireties.

[0169] Thermoreversible gelling agents, such as ester-terminated polyamides, tertiary amide-terminated polyamides, polyalkyleneoxy-terminated polyamides and polyetheramides and combinations thereof, may be desirable to us as thixotropic agents. Examples include Crystasense LP1, Crystasense LP2, Crystasense LP3, Crystasense MP, Crystasense HP4, Crystasense HP5, Rheoptima X17, Rheoptima X24, Rheoptima X38, Rheoptima X58, Rheoptima X73 and Rheoptima X84 available from Croda. Crystasense HP-5 is a preferred example of a thixotropic agent.

[0170] Metal oxides that have been surface treated to impart dispersibility characteristics compatible with the hardenable resin component may be desirable for use as thixotropic agents.

[0171] The thixotropic agent can be included in the photohardenable composition described herein in an amount ranging from, for example, about 0.05 weight percent to about 15 weight percent, about 0.5 weight percent to about 15 weight percent, about 0.5 weight percent to about 10 weight percent, about 0.5 weight percent to about 10 weight percent, about 1 weight percent to about 10 weight percent of the photohardenable composition. Other amounts may also be determined to be useful.

[0172] A thixotropic agent is preferably included in the photohardenable composition in an amount effective to at least partially restrict movement of the three-dimensional object, or one or more regions thereof, in the photohardenable composition during formation.

[0173] More preferably, the thixotropic agent is included in the photohardenable composition in an amount effective to at least partially restrict movement of a three-dimensional object suspended in the volume of the photohardenable composition (not in contact with a container surface) during formation. Most preferably, the position of the object in the volume of the photohardenable composition remains a fixed position during formation of the object.

[0174] Defoaming agent

[0175] Defoamers may be included to help remove air bubbles introduced during handling and processing.A preferred defoamer is BYK 1798 (a silicone based defoamer) available from BYK-Chemie GmbH (part of the ALTANA Group).

[0176] Stabilizer

[0177] Stabilizers may be included to improve the shelf life of the photohardenable composition and / or to control the level of cure and / or spatial resolution during printing. An example of a preferred stabilizer is TEMPO (2,2,6,6-tetramethylpiperidinyloxy free radical available from Sigma-Aldrich). Examples of other stabilizers include, but are not limited to, hindered phenols such as butylated hydroxytoluene; hydroquinone and its derivatives such as hydroquinone methyl ether; hindered amine light stabilizers; alkylated diphenylamines; and phosphites.

[0178] Deoxidizer

[0179] Oxygen scavengers may be included to react with oxygen (eg, singlet oxygen, dissolved oxygen) present in the photohardenable composition.

[0180] Non-reactive solvent diluent

[0181] Non-reactive solvent diluents may be included. Examples include, but are not limited to, acetone, amyl acetate, n-butanol, sec-butanol, tert-butanol, butyl acetate, cyclohexanone, decane, dimethylacetamide, dimethylformamide, dimethyl sulfoxide, dipropylene glycol, dipropylene glycol methyl ether, ethanol, ethyl acetate, ethylene glycol, glycerol, heptane, isopropanol, isopropyl acetate, methyl ethyl ketone, N-methylpyrrolidone, propylene carbonate, propylene glycol, propylene glycol diacetate, tetrahydrofuran, tripropylene glycol methyl ether, toluene, water, xylene.

[0182] Thermally activated free radical initiators

[0183] It may also be desirable to include a thermally activated free radical initiator in the photohardenable composition. Examples of thermally activated free radical initiators include, but are not limited to, 2,2'-azobis(2-methylpropionitrile), 1,1'-azobis(cyclohexanecarbonitrile), 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine] n-hydrate, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], organic peroxides, inorganic peroxides, peroxodisulfates.

[0184] Second light activated photoinitiator

[0185] Optionally, the photohardenable composition may further comprise a photoinitiator. Preferably, such photoinitiators do not significantly respond to light of the first wavelength or the second wavelength. It may be desirable to include a photoinitiator in conjunction with an optional post-treatment, including, for example, a post-curing step involving exposing the printed object to light (preferably in the UV range) after printing. A preferred example of a photoinitiator is Omnirad 184 (1-hydroxycyclohexyl-phenyl ketone) available from IGM. (Omnirad 184, IGM resin, CAS No. 947-19-3)

[0186] In the photohardenable compositions according to the present invention, the nature of the monomers, the photoconvertible photoinitiator and, where applicable, the amount of co-initiator and / or sensitizer will vary depending on the specific use of the composition, the emission characteristics of the exposure source, the development procedure, the desired physical properties of the polymerized product and other factors.

[0187] Examples of photohardenable compositions according to certain aspects of the present invention that include one or more co-initiators and / or sensitizers will generally have compositions falling within the following composition ranges in parts by weight [based on 100 parts total]:

[0188] The photohardenable resin component is about 10 to about 99.9999

[0189] The photoconvertible photoinitiator is about 0.0001 to about 0.5, including for example but not limited to about 0.0001 to about 0.1, about 0.0001 to about 0.05, about 0.0001 to about 0.02, about 0.0001 to about 0.01, about 0.0001 to about 0.009, about 0.0001 to about 0.005, about 0.0001 to about 0.0025, etc.

[0190] Coinitiator (optional) about 0.001 to about 10, including for example but not limited to about 0.001 to about 7.5, about 0.001 to about 5, about 0.001 to about 2.5, about 0.001 to about 1, about 0.001 to about 0.5, about 0.001 to about 0.25, and the like.

[0191] Sensitizer (optional) about 0.1 to 1, including, for example but not limited to, about 0.1 to about 0.75, about 0.1 to about 0.5, about 0.1 to about 0.25, etc.

[0192] Examples of photohardenable compositions according to certain aspects of the present invention that do not include one or more co-initiators and / or sensitizers will generally have compositions falling within the following composition ranges in parts by weight [based on 100 parts total]:

[0193] Photocurable resin component about 10 to 99.9999

[0194] The photoconvertible photoinitiator is about 0.0001 to about 0.5, including for example but not limited to about 0.0001 to about 0.1, about 0.0001 to about 0.05, about 0.0001 to about 0.02, about 0.0001 to about 0.01, about 0.0001 to about 0.009, about 0.0001 to about 0.005, about 0.0001 to about 0.0025, etc.

[0195] Coinitiator (optional) about 0.001 to about 10, including for example but not limited to about 0.001 to about 7.5, about 0.001 to about 5, about 0.001 to about 2.5, about 0.001 to about 1, about 0.001 to about 0.5, about 0.001 to about 0.25, and the like.

[0196] When the synergist is optionally further included in the photohardenable composition, it may be included within the above composition range in parts by weight [based on 100 parts in total].

[0197] The weight percent of the photohardenable resin component in the above exemplary compositions may be less than 10 weight percent, for example less than 5 weight percent, less than 3 weight percent, less than 2 weight percent, or 1 weight percent or less, in some cases, such as the case of printing hydrogels, where the remainder of the resin is composed of non-reactive components suspended in the final photohardening resin.

[0198] According to another aspect of the present invention, there is provided a hardenable resin composition useful for forming an object, the composition comprising:

[0199] (i) a photohardenable composition, wherein the photohardenable composition comprises a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator can be activated by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photoconvertible photoinitiator comprising a photochromic molecule, the photochromic molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule, or a spironaphthooxazine molecule, and wherein the substituted or unsubstituted α-diketone moiety is represented by the general formula (I):

[0200] Ar 1 -C(=O)-C(=O)-Ar 2

[0201] (I)

[0202] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl; and

[0203] (ii) a resin component that can be hardened by a heat-driven reaction or mechanism, the resin component comprising a monomer, an oligomer, a prepolymer, a polymer, or a mixture comprising at least one of the foregoing,

[0204] Preferably, the substituted or unsubstituted α-diketone moiety comprises an α-diketone moiety represented by any of the above formulae (IA) to (IK). As described above, optionally, any hydrogen attached to a ring member in any formula may alternatively comprise a substituent or moiety in its place.

[0205] It may be desirable for a photohardenable composition to exhibit non-Newtonian rheological behavior to be included in the hardenable resin according to the present invention.

[0206] It may be desirable for the hardenable resin composition to exhibit non-Newtonian rheological behavior.

[0207] The hardenable resin composition according to the present invention may also optionally contain any one or more of a thixotropic agent; a stabilizer; a light blocker containing a light absorbing pigment or dye; a non-reactive solvent diluent; a filler; a defoamer; an oxygen scavenger; a catalyst; and a thermal free radical initiator. Other additives may be included alternatively or additionally. Additional information about additives is provided above.

[0208] The photohardenable composition contained in the hardenable resin composition according to the present invention preferably includes the photohardenable composition described herein.

[0209] The hardenable resin composition according to the present invention comprises a resin component that can be hardened by a heat-driven reaction or mechanism. Examples of preferred heat-driven reactions or mechanisms include, but are not limited to, heating (e.g., direct or indirect application of heat or thermal energy, irradiation with microwaves, irradiation with UV, visible light or infrared light to achieve the purpose of heating). The resin component may comprise a monomer, an oligomer, a prepolymer, a polymer, or a mixture comprising at least one of the foregoing.

[0210] The inclusion of one or more resin components that can be hardened by a heat-driven reaction or mechanism in the hardenable resin composition described herein can facilitate or enable the formation of an article having characteristics and / or performance properties that can be suitable for end-use applications of articles formed from resins comprising the photohardenable composition, while the absence of the resin component may not be suitable. Examples of additional properties that can be modified by including a second resin component include, for example, but not limited to, mechanical properties, thermal properties, electrical properties, dielectric properties, chemical resistance, moisture resistance, and biocompatibility. Examples include improved mechanical properties, including increased tensile strength and modulus, flexural strength and modulus, compressive strength and modulus, impact strength, hardness, wear resistance, fatigue resistance, fracture toughness; improved thermal properties, including increased glass transition temperature, increased heat deformation temperature, increased thermal degradation temperature, or reduced thermal expansion coefficient; reduced moisture or solvent absorption; improved radiation resistance; improved fire resistance, flame retardancy, or carbon residue; improved dielectric properties (e.g., reduced dielectric constant, reduced dielectric loss constant, or increased breakdown voltage); or improved optical properties (e.g., increased refractive index).

[0211] Possible post-curing treatments for photohardenable compositions include, but are not limited to, application of light, heat, electron beam, time (aging), and humidity, as well as combinations of multiple such treatments in series or sequence. Light-based post-curing treatments for photohardenable compositions for 3D printing are commonly used and involve providing additional light exposure (e.g., LED, sunlight, medium-pressure mercury lamp, or fluorescent lamp) to a "green" (immature) printed object, typically at a slightly elevated temperature (e.g., 45° C. to 80° C.), and typically in a specially constructed apparatus (post-curing chamber) to the green object to reinitiate and further propagate the photoinitiated polymerization reaction (e.g., free radical polymerization of acrylates and methacrylates; cationic ring-opening polymerization of epoxides, oxetanes, and vinyl ethers) to achieve a higher overall conversion of photopolymerizable reactive groups in the post-cured object. Disadvantages of light-based post-curing are: incomplete or uneven penetration of light into the printed object, resulting in uneven curing; little or no effect on non-photocurable reactive groups; and the need for specialized equipment. The requirement for light penetration into the object is particularly problematic in highly pigmented compositions, filled compositions, and compositions where the photoinitiator does not photobleach.

[0212] Examples of suitable resin components include, but are not limited to, polyurethane, polyurethane-urea, and polyurea precursors; epoxy resins and epoxy curing agents; cyanate resins and phthalonitrile resins; maleimide resins, such as bismaleimide resins, alone or with allyl curing agents; polyimide and polyamideimide precursors, including, but not limited to, polyamic acid (e.g., poly(pyromellitic dianhydride-co-4,4'-oxydianiline)amic acid), polyamideamic acid (e.g., Torlon AI-30 and Torlon AI-50 available from Solvay), amines, anhydrides, and isocyanates; norbornene resins, such as nadic anhydride terminated resins; phenolic resins; and benzoxazine resins.

[0213] The hardenable resin composition according to the present invention may include, for example but not limited to, about 0.5 weight percent to about 95 weight percent, preferably about 40 weight percent to about 95 weight percent of a photohardenable resin component; about 0.0001 weight percent to about 0.5 weight percent of a photoconvertible photoinitiator, including but not limited to about 0.0001 weight percent to about 0.05 weight percent, 0.0001 weight percent to about 0.02 weight percent, about 0.0001 weight percent to less than about 0.02 weight percent of a photoconvertible photoinitiator; and about 0.5 weight percent to about 95 weight percent, and preferably about 15 weight percent to about 95 weight percent of a resin component.

[0214] The hardenable resin composition may further include, for example, any one or more of the following:

[0215] about 0.05 weight percent to about 15 weight percent, preferably about 0.5 weight percent to about 10 weight percent of a thixotropic agent,

[0216] From about 0.005 weight percent to about 1 weight percent of a defoaming agent,

[0217] From about 0.005 weight percent to about 10 weight percent of a light retarder,

[0218] From about 0.00005 weight percent to about 5 weight percent of an oxygen scavenger,

[0219] From about 0.05 weight percent to about 95 weight percent of a non-reactive solvent diluent,

[0220] About 0.00005 weight percent to about 10 weight percent of a catalyst

[0221] from about 0.05 weight percent to about 10 weight percent of a thermally activated free radical initiator, and

[0222] From about 0.5 weight percent to about 95 weight percent filler.

[0223] Unless otherwise indicated, amounts specified in weight percent are based on the total weight of the hardenable resin composition.

[0224] According to another aspect of the present invention, there is provided a method of forming an object, the method comprising:

[0225] (a) providing a volume containing a photohardenable composition, wherein the photohardenable composition comprises a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator is activatable by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photochromic molecule, the photochromic molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule, or a spironaphthooxazine molecule, and wherein the substituted or unsubstituted α-diketone moiety is represented by the general formula (I):

[0226] Ar 1 -C(=O)-C(=O)-Ar 2

[0227] (I)

[0228] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl;

[0229] (b) irradiating one or more selected locations within the volume of the photohardenable composition with light having a first wavelength and light having a second wavelength simultaneously or sequentially, wherein the light having the first wavelength and the light having the second wavelength activate the photoconvertible photoinitiator at the one or more selected locations to induce a crosslinking or polymerization reaction in the photohardenable composition at the intersection of the first and second wavelengths at the one or more selected locations within the volume to at least partially form an object; and

[0230] (c) optionally repeating step b) irradiating the photohardenable composition at one or more of the same or different selected locations in the volume until the object is partially or completely formed.

[0231] Preferably, the object at least partially formed in the photohardenable composition remains in a fixed position or is minimally displaced in the unhardened photohardenable composition during formation.

[0232] Preferably, the substituted or unsubstituted α-diketone moiety comprises an α-diketone moiety represented by any of the above formulae (IA) to (IK). As described above, optionally, any hydrogen attached to a ring member in any formula may alternatively comprise a substituent or moiety in its place.

[0233] Preferably, the photohardenable composition comprises the photohardenable composition described herein.

[0234] It may be desirable for photohardenable compositions to exhibit non-Newtonian rheological behavior in order to be included in the methods according to the present invention.

[0235] Preferably a volume of the photohardenable composition is contained within a container wherein at least one or more portions of the container are optically transparent so that light used to illuminate the photohardenable composition can contact the photohardenable composition. It may be desirable that the optically transparent portion of the container is also optically flat.

[0236] Examples of power densities of the first wavelength light include about 0.01 to about 100,000 W / cm 2 An example of a power density of the second wavelength light includes a power density of about 0.01 to about 100,000 W / cm 2 power density in the range.

[0237] Examples of the exposure energy of the first wavelength light include about 0.001 to about 1,000 mJ / cm 2 The exposure energy of the second wavelength light includes an exposure energy of about 0.01 to about 100,000 mJ / cm 2 Exposure energy within the range.

[0238] Methods according to certain aspects of the present invention, which include photohardenable compositions that exhibit non-Newtonian rheological behavior, can facilitate the formation of objects, preferably three-dimensional objects, that are completely suspended in a volume of the photohardenable composition during formation. The ability to completely suspend an object in a volume during formation advantageously eliminates the need to include support structures of the type used in stereolithography to maintain the geometry / shape of the object during formation (sometimes referred to as printing or 3D printing).

[0239] For use in forming objects, such as three-dimensional objects, it is desirable that the photohardenable composition does not harden (e.g., the photohardenable resin component does not undergo polymerization or crosslinking) when the photohardenable composition is exposed to only the first wavelength or only the second wavelength. In other words, the photohardenable composition does not polymerize in a volume that is exposed to two radiations at different or nearly simultaneous times (e.g., due to tightly timed sequential exposures). In particular, in scanning a volume of a photohardenable medium, there will be many such points in the volume, as the light beams pass through previously exposed areas or planes, and the points are scanned successively in an arbitrary order by the first wavelength radiation and the second wavelength radiation as the structure of the object is defined in the volume of the medium by the intersection of the light beams. Some points may also undergo multiple exposures to the first wavelength light and / or the second wavelength light. Preferably, points that receive such multiple consecutive (non-simultaneous) exposures will not polymerize.

[0240] Preferably, the amount of time that one or more selected locations within the volume are simultaneously or sequentially exposed to the first wavelength of light and the second wavelength of light is sufficient to induce the desired cross-linking or polymerization reaction in the photohardenable composition at the one or more selected locations and is insufficient to cause a change or hardening of the photohardenable composition when only one of the first and second wavelengths is present.

[0241] Preferably, light at said first wavelength and light at said second wavelength are projected into said volume as separate optical projections.

[0242] Preferably, the projection direction of the light of the first wavelength is orthogonal to the projection direction of the light of the second wavelength.

[0243] Preferably, the projection of light at the first wavelength comprises a light sheet. It may be desirable for the light sheet to comprise a planar light arrangement having opposing major faces, wherein the major faces are parallel to the direction in which the light sheet is directed into the volume.

[0244] Preferably, the projection of light of the second wavelength comprises the optical image perpendicular to the direction in which the optical image is projected into the volume.Preferably, a digital micromirror device (DMD) is employed in the projection of the optical image.

[0245] Preferably, the light sheet and the optical image intersect in a common plane. Desirably, the intersection of the light sheet and the optical image is coplanar or substantially coplanar.

[0246] The optical image may include any optical projection generated by an optical projection system. Examples of optical images include, but are not limited to, patterned or unpatterned two-dimensional images, light, or single point light. The two-dimensional image may include a cross section of the printed three-dimensional image. The two-dimensional image may represent a cross-sectional slice of the object to be printed. Such cross-sectional slices are typically generated using slicing software, as discussed elsewhere herein.

[0247] Examples of light sources that may be suitable for use with the methods described herein include, by way of example and not limitation, lasers, laser diodes, light emitting diodes, light emitting diodes (LEDs), micro-LED arrays, vertical cavity lasers (VCLs), and filter lamps. Such light sources are commercially available, and one of ordinary skill in the relevant art can readily select a suitable light source. It may be preferred to use a type of LED with the DMD, such as the Phlatlight LED available from Luminus. Other suitable light sources may also be used.

[0248] Optionally, the excitation light may be temporally and / or spatially modulated. Optionally, the intensity of the excitation light may be modulated.

[0249] Examples of projection devices for the methods described herein may include, but are not limited to, laser projection systems, liquid crystal displays (also referred to herein as “LCDs”), spatial light modulators (also referred to herein as “SLMs”) such as, but not limited to, digital micromirror devices (also referred to herein as “DMDs”), micro-LED arrays, vertical cavity laser arrays (also referred to herein as “VCLs”), vertical cavity surface emitting laser arrays (also referred to herein as “VCSELs”), liquid crystal on silicon (also referred to herein as “LCoS”) projectors, and scanning laser systems. (Light emitting diodes are also referred to herein as “LEDs”).

[0250] The optical image projection system may optionally further comprise one or more optical components (eg, projection optics, illumination optics, lenses, lens systems, mirrors, prisms, etc.).

[0251] The methods of the invention described herein may further include post-processing. Examples of post-processing steps that may be further included in the methods according to the invention include, but are not limited to, one or more of the following: separation of the at least partially hardened composition from the unhardened composition, washing, post-curing (e.g., by light, heat, ionizing radiation, pressure or a combination of techniques simultaneously or sequentially), metering, freeze drying, critical point drying and packaging.

[0252] In the method for forming a three-dimensional object according to the present invention, it is desirable to select a photoconvertible photoinitiator molecule whose first excitation wavelength has significant absorption of the first form, and wherein the second form of the photoinitiator has minimal absorption of the first excitation wavelength. This has two advantages, first, it simplifies exposure (exposure), because the activation of the photoconvertible photoinitiator can occur without activating its second form to cause a crosslinking or polymerization reaction in the photohardenable resin component. When there is a large amount of overlap, the intensity of the two radiations must be carefully controlled so that the photoconvertible photoinitiator molecules are activated while minimizing the activation of its second form. Second, it can allow deeper penetration of the volume or layer of the composition, because converting the photoconvertible photoinitiator to its second form has the effect of "bleaching" the photoconvertible photoinitiator molecule or making it transparent with respect to the first wavelength radiation.

[0253] The preparation of the photohardenable composition according to the invention is carried out in a manner known or conventional otherwise, for example, the solvent for the monomers can be used to remove the photohardenable composition in the unexposed areas. The monomers most typically used herein are known in the art, as are their solvents.

[0254] In general, the photoconvertible photoinitiators useful in the photohardenable compositions and methods described herein can absorb at about 300 to 550 nm. Other examples of ranges in which the photoconvertible photoinitiators absorb light include, but are not limited to, about 350 to about 410 nm, about 375 nm ± 10 nm, and about 405 nm ± 10 nm. Depending on the extinction coefficient of the particular photoconvertible photoinitiator, conversion to the second form can be induced by exposure to any source (e.g., laser, light emitting diode, mercury lamp) that emits within this range. Filters can be used to limit the output wavelength. Non-limiting examples of filtered light include filtered emission from a mercury arc lamp, etc.

[0255] The second form of the photoconvertible photoinitiator will preferably absorb in the range of about 450 to 1000 nm and most typically 450 to 850 nm. Other examples of the range that the second form of the photoconvertible photoinitiator preferably absorbs include 450 to about 700 nm. This form can be activated by a second excitation light to directly generate free radicals or generate excitons, which undergo electron transfer or hydrogen abstraction (optionally via electrons, hydrogen or energy to the co-initiator or synergist (one or more) of the aspects of the present invention including one or more co-initiators) by exposure to any second wavelength in the range. For the second excitation, the exposure (exposure) can be completed using a laser source, an LED or LED array, filtered emission from an arc lamp, or other suitable source with emission in the desired wavelength range. Argon ions, He-Ne, laser diodes, krypton, frequency-doubled Nd-YAG, etc. Other light sources can be used, optionally with filters to limit the output wavelength, for example, light emitting diodes, incandescent lamps, halogen lamps, mercury lamps, arc lamps, etc.

[0256] Optionally, the photohardenable composition included in the method according to the present invention may further include a second light-activated photoinitiator, which preferably has no significant response to light of the first wavelength or the second wavelength. It may be desirable to include a second light-activated photoinitiator in connection with an optional post-curing step to be performed, for example, by using UV light as part of any post-treatment of the printed object after printing. If the second light-activated photoinitiator is included in the photohardenable composition for post-curing purposes, the method may further include a post-curing step, the post-curing step comprising exposing the object to light of a third wavelength to further harden the object, the third wavelength being different from the first and second wavelengths. The irradiation with the third wavelength is preferably performed after removing or separating the partially hardened portion from the volume in which it is formed. It may be desirable to wash the separated or removed portion before post-curing irradiation with the third wavelength. When the photoinitiator is UV-activatable, the third wavelength is preferably in the ultraviolet range. A third wavelength in a range of, for example, about 240 to about 455 nm, about 240 nm to about 445 nm, about 240 nm to about 410 nm, or other ranges less than the first and second wavelengths may be used.

[0257] It may be desirable that the photohardenable composition and / or the hardenable resin composition contained in the method according to the present invention further contains a thermally activated free radical initiator.

[0258] According to another aspect of the present invention, there is provided a method of forming an object, comprising:

[0259] (a) providing a volume of a hardenable resin composition, wherein the hardenable resin composition comprises (i) a photohardenable composition; and (ii) a resin component that is hardenable by a heat-driven reaction or mechanism, the resin component comprising a monomer, an oligomer, a prepolymer, a polymer, or a mixture comprising at least one of the foregoing, wherein the photohardenable composition comprises a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator is activatable by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photoconvertible photoinitiator comprising a photochromic molecule, the photochromic molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule, or a spironaphthooxazine molecule, and wherein the substituted or unsubstituted α-diketone moiety is represented by the general formula (I):

[0260] Ar 1 -C(=O)-C(=O)-Ar 2

[0261] (I)

[0262] Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl;

[0263] (b) forming an intermediate object from the hardenable resin composition, wherein the forming of the intermediate object comprises:

[0264] (i) irradiating one or more selected locations within the volume of the hardenable resin composition with light having a first wavelength and light having a second wavelength simultaneously or sequentially, wherein the light having the first wavelength and the light having the second wavelength activate the photo-switchable photoinitiator at the one or more selected locations to induce a crosslinking or polymerization reaction in the photohardenable composition at the intersection of the first and second wavelengths at the one or more selected locations within the volume to at least partially form an object; and

[0265] (ii) optionally repeating step (i) at one or more of the same or different selected locations within the volume of the hardenable resin composition until an intermediate object is formed; and

[0266] (c) hardening (e.g., further reacting, further polymerizing, further chain extending) the resin components in the intermediate object through a heat-driven reaction or mechanism to form the object.

[0267] Preferably, the photo-switchable photoinitiator comprises a benzospiropyran molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety, a naphthopyran molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety, and a spironaphthoxazine molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety.

[0268] Preferably, the substituted or unsubstituted α-diketone moiety comprises an α-diketone moiety represented by any of the above formulae (IA) to (IK). As described above, optionally, any hydrogen attached to a ring member in any formula may alternatively comprise a substituent or moiety in its place.

[0269] Preferably, the photohardenable composition comprises the photohardenable composition described herein.

[0270] It may be desirable for photohardenable compositions to exhibit non-Newtonian rheological behavior in order to be included in the methods according to the present invention.

[0271] It may be desirable for the hardenable resin composition to exhibit non-Newtonian rheological behavior in order to be included in the method according to the present invention.

[0272] The hardenable resin composition for inclusion in the method of the present invention comprises the hardenable resin composition according to the present invention.

[0273] Optionally, the photohardenable composition in the hardenable resin composition or in the hardenable composition in the method according to the present invention may further comprise a second light-activated photoinitiator, which preferably has no significant response to light of the first wavelength or the second wavelength. It may be desirable to include a second light-activated photoinitiator in connection with an optional post-curing step to be performed, for example, by using UV light after printing as part of any post-treatment of the printed object. If the second light-activated photoinitiator is included in the photohardenable composition for post-curing purposes, the method may further comprise a post-curing step, the post-curing step comprising exposing the object to light of a third wavelength to further harden the object, the third wavelength being different from the first and second wavelengths. The irradiation with the third wavelength is preferably performed after removing or separating the partially hardened portion from the volume in which it is formed. It may be desirable to wash the separated or removed portion before post-curing irradiation with the third wavelength. When the photoinitiator is UV-activatable, the third wavelength is preferably in the ultraviolet wavelength range. A third wavelength in a range of, for example, about 240 to about 455 nm, about 240 nm to about 445 nm, about 240 nm to about 410 nm, or other ranges less than the first and second wavelengths can be used.

[0274] If a second light activated photoinitiator is further included in the hardenable resin composition, the intermediate object may be further irradiated with a third wavelength for hardening before, during or after the step including further hardening by a thermally driven reaction or hardening mechanism.

[0275] The photohardenable composition and the hardenable resin composition contained in the method according to the present invention may desirably further contain a thermally activated free radical initiator.

[0276] Preferably, a volume of the hardenable resin composition is contained within a container, wherein at least one or more portions of the container are optically transparent so that light used to illuminate the photohardenable composition contained therein can contact the photohardenable composition. It may be desirable that the optically transparent portion of the container is also optically flat.

[0277] Examples of power densities of the first wavelength light include about 0.01 to about 100,000 W / cm 2 An example of a power density of the second wavelength light includes a power density of about 0.01 to about 100,000 W / cm 2 power density in the range.

[0278] Examples of the exposure energy of the first wavelength light include about 0.001 to about 1,000 mJ / cm 2 The exposure energy of the second wavelength light includes an exposure energy of about 0.01 to about 100,000 mJ / cm 2 Exposure energy within the range.

[0279] Methods according to certain aspects of the present invention, which include a photohardenable composition exhibiting non-Newtonian rheological behavior and a hardenable resin composition, can facilitate forming an object, preferably a three-dimensional object, that is completely suspended in a volume of the photohardenable composition during formation. The ability to completely suspend an object in a volume during formation advantageously eliminates the need for support structures of the type used in stereolithography to maintain the geometry / shape of the object during formation (sometimes referred to as printing or 3D printing).

[0280] For use in forming objects, such as three-dimensional objects, it is desirable that the photohardenable composition does not harden (e.g., the photohardenable resin component does not undergo polymerization or crosslinking) when the photohardenable composition is exposed to only the first wavelength or only the second wavelength. In other words, the photohardenable composition does not polymerize when hardened in a volume that is exposed to two radiations at different or nearly simultaneous times (e.g., due to tightly timed sequential exposures). In particular, in scanning a volume of a photohardenable medium, there will be many such points in the volume that are scanned successively in an arbitrary order by the first wavelength radiation and the second wavelength radiation as the structure of the object is defined in the volume of the medium by the intersection of the beams. Some points may also undergo multiple exposures to the first wavelength light and / or the second wavelength light. It may be desirable to select photoconvertible photoinitiators that reverse when they are not exposed to the first wavelength light.

[0281] Preferably, the amount of time that one or more selected locations within the volume are simultaneously or sequentially exposed to the first wavelength of light and the second wavelength of light is sufficient to induce the desired cross-linking or polymerization reaction in the photohardenable composition at the one or more selected locations, and is insufficient to cause a change or hardening of the photohardenable composition when only one of the first and second wavelengths is present.

[0282] Preferably, light at said first wavelength and light at said second wavelength are projected into said volume as separate optical projections.

[0283] Preferably, the projection direction of the light of the first wavelength is orthogonal to the projection direction of the light of the second wavelength.

[0284] Preferably, the projection of light at the first wavelength comprises a light sheet. It may be desirable for the light sheet to comprise a planar light arrangement having opposing major faces, wherein the major faces are parallel to the direction in which the light sheet is directed into the volume.

[0285] Preferably, the projection of light of the second wavelength comprises the optical image perpendicular to the direction in which the optical image is projected into the volume.Preferably, a digital micromirror device (DMD) is employed in the projection of the optical image.

[0286] Preferably, the light sheet and the optical image intersect in a common plane. Desirably, the intersection of the light sheet and the optical image is coplanar or substantially coplanar.

[0287] The optical image may include any optical projection generated by an optical projection system. Examples of optical images include, but are not limited to, patterned or unpatterned two-dimensional images, light, or single point light. The two-dimensional image may include a cross section of the printed three-dimensional image. The two-dimensional image may represent a cross-sectional slice of the object to be printed. Such cross-sectional slices are typically generated using slicing software, as discussed elsewhere herein.

[0288] Preferably, the projection direction of the light of the first wavelength is orthogonal to the projection direction of the optical image.

[0289] Preferably, the projection of light at the first wavelength comprises a light sheet. It may be desirable for the light sheet to comprise a planar light arrangement having opposing major faces, wherein the major faces are parallel to the direction in which the light sheet is directed into the volume.

[0290] Preferably, the projection of light of the second wavelength comprises the optical image perpendicular to the direction in which the optical image is projected into the volume.Preferably, a digital micromirror device (DMD) is employed in the projection of the optical image.

[0291] Preferably, the light sheet and the optical image intersect in a common plane. Desirably, the intersection of the light sheet and the optical image is coplanar or substantially coplanar.

[0292] Examples of light sources for excitation light that may be suitable for the methods described herein include, by way of example and not limitation, lasers, laser diodes, light emitting diodes, light emitting diodes (LEDs), micro-LED arrays, vertical cavity lasers (VCLs), and filter lamps. Such light sources are commercially available, and one of ordinary skill in the relevant art can readily select a suitable light source. A type of LED such as the Phlatlight LED available from Luminus may preferably be used with a DMD. Other suitable light sources may also be used.

[0293] Optionally, the excitation light may be temporally and / or spatially modulated. Optionally, the intensity of the excitation light may be modulated.

[0294] Examples of projection devices for the methods described herein may include, but are not limited to, laser projection systems, liquid crystal displays (also referred to herein as “LCDs”), spatial light modulators (also referred to herein as “SLMs”) such as, but not limited to, digital micromirror devices (also referred to herein as “DMDs”), micro-LED arrays, vertical cavity laser arrays (also referred to herein as “VCLs”), vertical cavity surface emitting laser arrays (also referred to herein as “VCSELs”), liquid crystal on silicon (also referred to herein as “LCoS”) projectors, and scanning laser systems. (Light emitting diodes are also referred to herein as “LEDs”).

[0295] The optical image projection system may optionally further comprise one or more optical components (eg, projection optics, illumination optics, lenses, lens systems, mirrors, prisms, etc.).

[0296] The methods of the invention described herein may further include post-processing. Examples of post-processing steps that may be further included in the methods according to the invention include, but are not limited to, one or more of the following: separation of the at least partially hardened composition from the unhardened composition, washing, post-curing (e.g., by light, heat, ionizing radiation, pressure or a combination of techniques simultaneously or sequentially), metering, freeze drying, critical point drying and packaging.

[0297] In the method for forming a three-dimensional object according to the present invention, it is desirable to select a photoconvertible photoinitiator molecule whose first excitation wavelength has significant absorption of the first form, and wherein the second form of the photoinitiator has minimal absorption of the first excitation wavelength. This has two advantages, first, it simplifies exposure (exposure), because the activation of the photoconvertible photoinitiator can occur without activating its second form to cause a crosslinking or polymerization reaction in the photohardenable resin component. When there is a large amount of overlap, the intensity of the two radiations must be carefully controlled so that the photoconvertible photoinitiator molecules are activated while minimizing the activation of its second form. Second, it can allow deeper penetration of the volume or layer of the composition, because converting the photoconvertible photoinitiator to its second form has the effect of "bleaching" the photoconvertible photoinitiator molecule or making it transparent with respect to the first wavelength radiation.

[0298] The preparation of the photohardenable composition according to the invention is carried out in a manner known or conventional otherwise, for example, the solvent for the monomers can be used to remove the photohardenable composition in the unexposed areas. The monomers most typically used herein are known in the art, as are their solvents.

[0299] In general, the photoconvertible photoinitiators described herein may be expected to absorb in their first form at about 300 to 550 nm, including, for example, but not limited to, about 350 to about 460 nm, about 350 to about 455 nm, about 350 nm to about 445 nm, about 350 nm to about 410 nm, about 375 to about 455 nm, about 375 to about 445 nm, about 375 nm to about 405 nm. Depending on the extinction coefficient of the particular photoconvertible photoinitiator, conversion to the second form may be induced by exposure to any source (e.g., laser, light emitting diode, mercury lamp) emitting within this range. Filters may be used to limit the output wavelength. Non-limiting examples of filtered light include filtered emission from a mercury arc lamp, etc.

[0300] The second form of the photoconvertible photoinitiator will preferably absorb in the range of about 450 to about 1000 nm and most typically about 450 to about 850 nm. Other examples of the range in which the second form of the photoconvertible photoinitiator preferably absorbs include about 450 to about 700 nm. This form can be activated by a second excitation light to directly generate free radicals or generate excitons, which undergo electron transfer, hydrogen abstraction (optionally via electrons, protons or energy to the co-initiator or synergist (one or more) of the aspects of the present invention including one or more co-initiators) by exposure to any second wavelength in the range. For the second excitation, the exposure (exposure) can be completed using a laser source, an LED or LED array, filtered emission from an arc lamp, or other suitable source with emission in the desired wavelength range. Argon ions, He-Ne, laser diodes, krypton, frequency-doubled Nd-YAG, etc. Other light sources can be used, optionally with filters to limit the output wavelength, for example, light emitting diodes, incandescent lamps, halogen lamps, mercury lamps, arc lamps, etc.

[0301] The photohardenable composition and the hardenable resin composition contained in the method according to the present invention may desirably further contain a thermally activated free radical initiator.

[0302] A printed object prepared from a hardenable resin composition comprising a resin component that can be hardened by a heat-driven reaction or mechanism may be referred to as a "green" object prior to post-curing, which includes a heat-driven reaction or mechanism to harden the thermally hardenable resin component.

[0303] In the methods described herein involving hardenable resin compositions, once the intermediate article is formed, it can be removed from the hardenable resin composition, optionally washed, optionally subjected to any other modifications, and then subjected to a thermally driven reaction or mechanism (e.g., heating and / or microwave irradiation) sufficient to further harden (e.g., by further reaction, further polymerization, further chain extension) the hardenable resin component and form the article. Additional modifications may also be made to the formed article after the heating and / or microwave irradiation steps.

[0304] Separation of the at least partially cured material (ie, the intermediate article) from the unhardened composition can be performed by a variety of means known in the art, such as gravity drainage, screening, air knives, centrifugation, vibration, or ultrasonic agitation.

[0305] Any suitable organic or aqueous washing liquid or combination thereof, including solutions, suspensions, emulsions, microemulsions, etc., may be used for washing. Examples of suitable washing liquids include, but are not limited to, water, alcohols (e.g., methanol, ethanol, isopropanol, etc.), glycol ethers, benzene, toluene, etc. Washing liquids comprising a mixture of two or more liquids (e.g., water and an alcohol (e.g., isopropanol)) may also be suitable. Such washing solutions may optionally contain additional ingredients, such as surfactants, etc.

[0306] As described above, after the intermediate article is formed, optionally washed, etc., it can be further hardened by a heat-driven reaction or mechanism. Hardening can include heating and / or microwave irradiation to further solidify it. Heating can be active heating (e.g., in an oven, such as an electric oven, a gas oven, or a solar oven), or passive heating (e.g., at ambient temperature). Active heating can be faster than passive heating and can be preferred in some embodiments. Passive heating can also be expected, for example, by maintaining the intermediate at ambient temperature for a sufficient time to achieve further curing. Optionally, heating can include heating at a first temperature for a first time period, then heating at a second temperature for a second time period, then heating at a third temperature for a third time period, and so on, for any number of temperatures and time periods. Temperatures and time periods can be selected to facilitate volatiles to evaporate from the article without causing damage (e.g., cracks); to facilitate more complete curing of lower temperature curing components, to stabilize the article shape before subsequent curing of higher temperature curing components; or to develop higher thermomechanical properties. Differential scanning calorimetry can help determine the temperature and time period suitable for curing by indicating the temperature at which the curing reaction begins and reaches its maximum rate (e.g., in experiments with temperature ramps) and indicating how much time is required to complete the curing reaction (e.g., in isothermal experiments). The time periods may be the same length or different lengths. In certain embodiments, the first temperature may be ambient temperature or above ambient temperature, and each subsequent temperature may be higher than the previous temperature. Preferably, the maximum temperature is sufficient to completely or substantially completely harden or cure the hardenable resin composition, but below the degradation temperature, such as the 5% mass loss temperature measured by thermogravimetric analysis. When multiple temperatures are used, the temperature may be ramped, such as increased in a stepwise manner.

[0307] For example, the intermediate can be heated in a stepwise manner at a first temperature in a first range (e.g., from about 70°C to about 150°C), then at a second temperature in a second range (e.g., from about 150°C to 200°C or from about 150°C to about 250°C), wherein the duration of each heating depends on the size and shape of the intermediate article. In another embodiment, the intermediate can be cured by a ramped heating scheme, wherein the temperature is ramped from a first temperature (e.g., ambient temperature or a temperature greater than ambient temperature) through a second temperature (e.g., a temperature in a range greater than the first temperature) such as 150°C, and up to a final temperature (e.g., a temperature greater than the second temperature) to, for example, about 250°C, with a change in heating rate of, for example, 0.5°C per minute to 5°C per minute.

[0308] The objects (which may also be referred to herein as articles or parts) formed by the methods described herein including a hardening step including a heat-driven reaction or mechanism may be the same or different from the intermediate article prior to further hardening including a heat-driven reaction or mechanism. For example, there may be variations between the intermediate article and the article due to, for example, shrinkage (e.g., up to 1%, 2%, 5%, 10%, 25%, or 50% by volume), expansion (e.g., up to 1%, 2%, 5%, 10% by volume), or possible optional intervening forming steps (e.g., intentional bending, stretching, drilling, grinding, cutting, polishing, or other intentional forming after the intermediate product is formed but before subsequent article formation). Preferably, the intermediate article may have the same shape as the article to be formed or may have a shape to be imparted to the article to be formed.

[0309] The method according to various aspects of the present invention may further include post-processing the formed three-dimensional object.

[0310] Examples of post-processing include, but are not limited to, washing, post-curing (e.g., by light, electron beam, heat, non-ionizing radiation, ionizing radiation, time (aging), pressure, humidity, or a simultaneous or sequential combination of techniques), metering, labeling or tracking (e.g., by barcodes, QR codes, or RFID tags), freeze-drying processes, critical point drying, and packaging.

[0311] In the methods described herein including light sheets, the light sheets may be constructed by means known in the art, including but not limited to techniques including lasers and Powell lenses, galvanometers, and / or polygon scanning mirrors. Alternatively, one or more LEDs may be used as the light source.

[0312] Optionally, the methods described herein may further include using a different additional wavelength to force the second form of the photo-switchable photoinitiator to reverse react back to the original / starting form to help avoid hardening of unwanted areas.

[0313] As used herein, the first wavelength, the second wavelength, and the third wavelength may refer to a range of wavelengths.

[0314] In the methods described herein, preferably the first wavelength and the second wavelength are generated by different light sources or different optical projection or other optical systems.

[0315] The method according to the present invention preferably comprises providing a volume of a photohardenable composition as described herein or a hardenable resin composition as described herein, contained in a container, wherein at least a portion of the container is optically transparent so that the photohardenable composition is accessible to the excitation light. Optionally, the entire container is optically transparent.

[0316] The optically transparent portion of the container can be constructed from materials including, for example, but not limited to, glass, quartz, fluoropolymers (e.g., Teflon FEP, Teflon AF, Teflon PFA), cyclic olefin copolymers, polymethyl methacrylate (PMMA), polynorbornene, sapphire, or transparent ceramics.

[0317] Examples of container shapes include, but are not limited to, cylindrical containers with circular or oval cross-sections, containers with straight sides and polygonal cross-sections, or rectangular or square cross-sections.

[0318] Preferably, the optically transparent portion(s) of the container are also optically flat.

[0319] Optionally, one or more filters may be added to at least one surface of any optically transparent portion of the container to block undesirable light, such as room light, to prevent unintended curing.

[0320] Optionally, the photohardenable composition is filtered to remove particles prior to introduction into the container. Optionally, air bubbles are removed from the photohardenable composition prior to or after introduction into the container. Optionally, the photohardenable composition is degassed, purged or sprayed with an inert gas prior to or after introduction into the container. Optionally, the photohardenable composition is maintained under inert conditions during printing, for example, under an inert atmosphere. This prevents oxygen from being introduced into the container while the object is being printed or formed.

[0321] In the methods described herein, the container can be rotated to provide additional angles of illumination or projection of the excitation light into the volume containing the photohardenable composition. This can be helpful in more accurately mapping the volume or surface of an object or it can be used as a means to provide multiple exposures of a given feature from different angles.

[0322] In the methods described herein, the container can be stationary while a beam or optical projection of excitation light is being directed into the photohardenable composition.

[0323] The methods disclosed herein may also include the use of commercially available light projection or filtering techniques and systems that employ two or more light projection methods simultaneously.

[0324] Before printing, a digital file of the object to be printed is obtained. If the digital file is not in a format that can be used to print the object, the digital file is converted into a format that can be used to print the object. Examples of typical formats that can be used for printing include, but are not limited to, STL files. Typically, the STL file is then sliced ​​into two-dimensional layers using three-dimensional slicer software and converted into G-Code or a set of machine commands, which facilitates the construction of the object. See B. Redwood et al., "The 3D Printing Handbook-Technologies, designs applications", 3D HUBSB.V.2018.

[0325] Examples of sources for excitation light sources used in the methods described herein include laser diodes, such as those commercially available, light emitting diodes, DMD projection systems, micro-LED arrays, vertical cavity lasers (VCL). In some embodiments, the excitation radiation source (e.g., light source) is a light emitting diode (LED).

[0326] The excitation light can be directed into the volume of the photohardenable composition in a continuous or intermittent manner. Intermittent excitation can include applying light randomly on and off or applying light periodically. Examples of periodically applying light include pulses. Alternatively, excitation can be applied as a combination of both continuous excitation light and intermittent light, including, for example, irradiating with continuous light before or after applying intermittent excitation light.

[0327] Available information in conjunction with various aspects of the present invention includes International Patent Application No. PCT / US2022 / 052157 filed by Quadratic 3D, Inc. on December 7, 2022 and International Patent Application No. PCT / US2022 / 039766039766 filed by Quadratic 3D, Inc. on August 9, 2022, each of which is hereby incorporated by reference in its entirety.

[0328] Other information on optical systems that may be used in conjunction with various aspects of the present invention includes Texas Instruments Application Report DLPA022-July 2010 entitled "DLP TMSystem Optics”; Texas Instruments “TIDLR Technology for 3D Printing–Design scalable high-speedstereolithography [sic] systems using TIDLP technology” 2016; Texas Instruments “DLP6500 0.65 1018p MVSP Type A DMD”, DLP6500, DLPS040A-October 2014-Revised October 2016; and YH Lee et al., “Fabrication of Periodic 3D Nanostructuration for Optical Surfaces by Holographic Two-Photon-Polymerization”, Int'l Journal of Information and Electronics Engineering, Vol 6, No. 3, May 2016, each of the foregoing is hereby incorporated by reference in its entirety into this article. Example

[0329] The examples provided herein are intended to be illustrative only and not limiting, and various modifications of the exemplary compositions and methods are contemplated and are within the scope of the present invention.

[0330] Example 1 - Preparation of Photoconvertible Photoinitiator

[0331] Synthetic Bpin-Ben:

[0332]

[0333] To a 250 mL round bottom flask was added 1-(4-bromophenyl)-2-phenylethane-1,2-dione (10.0 g, 34.6 mmol, 1.0 equiv), bis(pinacol)diboron (9.66 g, 38 mmol, 1.1 equiv), XPhos Pd G2 (0.82 g, 1.04 mmol, 0.03 equiv, CAS: 1310584-14-5), potassium acetate (8.5 g, 87 mmol, 2.5 equiv) and a magnetic stir bar. The flask was sealed with a rubber septum and placed under N2 atmosphere for three vacuum / N2 cycles. Anhydrous deoxygenated dioxane (36 mL) was added via syringe and the flask was sealed with electrical tape. The mixture was stirred at 90 °C (heat block temperature) for 12 h, then the mixture was warmed to room temperature and diluted with CH2Cl2 (100 mL). The mixture was filtered through a short silica gel column (40 g). The column was flushed with 20% EtOAc / CH2Cl2 (~200 mL) until no further product was observed by thin layer chromatography. The filtrate was concentrated by rotary evaporation and the crude oil was recrystallized from hexanes (200 mL) at -78 °C to give Bpin-Ben (1-phenyl-2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolaborane-2-yl)phenyl)ethane-1,2-dione) (11.0 g, 95%) as a light yellow solid. 1 H NMR (400MHz, C6D6) δ8.05–7.96(m,4H),7.90–7.85(m,2H),7.05–6.99(m,1H),6.94–6.88(m,2H),1.07(s,12H).

[0334] Compound NO17 shown in the synthetic formula IIIA:

[0335]

[0336] To a 40 mL screw-cap amber vial was added compound A (2.06 g, 11.9 mmol, 1.00 equiv), compound B (3.00 g, 11.9 mmol, 1.00 equiv), anhydrous ethanol (12 mL), and a magnetic stir bar. The vial was sealed and the stirred mixture was heated at 90 °C (heat block temperature) for 2 h. The volatiles were removed by rotary evaporation at 35 °C. To ensure the removal of ethanol (small amounts of ethanol can affect subsequent purification), the residue was dissolved in toluene (20-30 mL) and the volatiles were removed by rotary evaporation at 35 °C. The residue was subjected to silica gel chromatography (33–50% CH2Cl2 in hexanes) to give the desired bromospironaphthoxazine intermediate C as a light brown solid. The solid was analyzed by thin layer chromatography (50% CH2Cl2 in hexanes) and used without further purification or characterization.

[0337] To a 20 mL screw-cap amber vial was added bromo-spironaphthoxazine C (50 mg, 0.12 mmol, 1.0 equiv), Bpin-Ben (45 mg, 0.14 mmol, 1.1 equiv), [1,1'-bis(diphenylphosphino)ferrocene]-palladium dichloride (3.0 mg, 0.0037 mmol, 0.03 equiv), potassium carbonate (85 mg, 0.61 mmol, 5.0 equiv) and a magnetic stir bar. The vial was sealed and placed under N2 atmosphere for three vacuum / N2 cycles. A deoxygenated 5 / 1 (v / v) mixture of dioxane / water (3 mL) was added to the vial via syringe and the vial was sealed with electrical tape. The mixture was stirred vigorously at 90°C (heat block temperature) for 2 h and then the volatiles were removed by rotary evaporation at 35°C. The residue was chromatographed on silica gel (100% CH2Cl2) to afford NO17 (45 mg, 68%) as a light green solid. 1 H NMR(400MHz,C6D6)δ9.10(d,J=8.8Hz,1H),8.09–8.05(m,2H),8.05–8.00(m,2 H),7.70(d,J=1.8Hz,1H),7.67(s,1H),7.62(dd,J=8.8,1.9Hz,1H),7.41–7.33 (m,3H),7.12(dd,J=7.5,1.8Hz,1H),7.10–7.04(m,1H),7.01–6.95(m,2H),6. 92–6.83(m,3H),6.35(d,J=7.8Hz,1H),2.47(s,3H),1.27(s,3H),1.10(s,3H).

[0338] Compound NP31 shown in the synthetic formula IIIA:

[0339]

[0340] A dry 250 mL two-necked round bottom flask is placed under a nitrogen atmosphere and bis(4-bromophenyl)methanone (2.50 g, 7.35 mmol, 1.0 equivalent) and dry THF (25 mL) are added. Propynylmagnesium bromide (0.5 M THF solution, 22 mL, 11 mmol, 1.5 equivalents) is then added to the solution via a syringe within 5-10 minutes. The mixture is heated at 50 ° C for 3 hours, after which time TLC shows that the starting material is completely consumed. The mixture is carefully quenched with saturated NH4Cl aqueous solution (100 mL). The mixture is extracted with ethyl acetate (100 mL), and the organic layer is washed with water (100 mL) and saturated NaCl aqueous solution (100 mL), dried over sodium sulfate, and filtered. The filtrate is concentrated by rotary evaporation and the residual solvent is removed under high vacuum to obtain a light yellow oily alkynol D (2.5 g), which is used in the next step without further purification or characterization.

[0341] To a dry 100 mL two-necked flask equipped with an air condenser and a magnetic stirrer was added 4-methoxynaphthalene-1-ol (0.75 g, 4.31 mmol, 1.0 equiv), alkynol D (1.64 g, 4.31 mmol, 1.0 equiv) and pyridinium p-toluenesulfonate (PPTS, 54 mg, 0.05 equiv). The flask was placed under a N2 atmosphere and anhydrous dichloroethane (40 mL) and trimethyl orthoformate (0.914 g, 2.0 equiv) were added. The mixture was heated to 85°C (heating block temperature) and maintained at this temperature until one of the starting materials was consumed as determined by TLC. The reaction mixture was cooled to room temperature, volatiles were removed by rotary evaporation, and the residue was subjected to silica gel chromatography (ethyl acetate / hexane eluent) to afford bromonaphthopyran E (1.7 g, 73%) as a light yellow solid.

[0342] To a 20 mL screw-cap amber vial equipped with a magnetic stir bar was added bromonaphthopyran E (50 mg, 0.09 mmol, 1.0 equiv), Bpin-Ben (69 mg, 0.21 mmol, 2.2 equiv), [1,1'-bis(diphenylphosphino)ferrocene]-palladium dichloride (3.8 mg, 0.05 equiv) and potassium carbonate (103 mg, 0.75 mmol, 8.0 equiv). The vial was sealed and placed under an N2 atmosphere for three vacuum / N2 cycles. A deoxygenated 5 / 1 mixture (v / v) of dioxane / water (4 mL) was then added to the vial via syringe. The stirred mixture was heated at 80°C (heat block temperature) for 2-6 hours (until the reaction was complete as indicated by TLC). The volatiles were removed by rotary evaporation at 35°C and the residue was subjected to silica gel chromatography (CH2Cl2) to afford NP31 as a light yellow solid. 1H NMR (400MHz, C6D6) δ8.66(d,J=8.3Hz,1H),8.44(d,J=8.4Hz,1H),7.99–7.94(m,8H),7.78–7.73(m,4H),7.46–7.41(m,1H),7.35–7.29( m,5H),7.27–7.21(m,4H),7.07–7.01(m,2H),6.98–6.92(m,4H),6.49(s,1H),6.03(q,J=1.7Hz,1H),3.43(s,3H),2.04(d,J=1.5Hz,3H).

[0343] Example 2 - Preparation of base resin

[0344] 12.0g thixotropic agent (Crystasense HP-5, Croda) is weighed into a large plastic weighing boat and then poured into a 100mL 24 / 40 round-bottomed flask containing a magnetic stirring bar. 50.0gN, N-dimethylacrylamide (DMAA, Rahn) is added to the flask by a 24mL syringe with a 4-inch 16G needle. The flask is closed with a rubber septum, a 1-inch 22G needle is inserted through the rubber septum for exhaust, and the flask is placed in an aluminum heating block preheated on a hot plate, set to stir at 105°C and 250-300rpm. After 10-15 minutes, the thixotropic agent is completely dissolved. Next, 50.0g DMAA is added to a 0.6-gallon polypropylene bucket with a polypropylene cap by a syringe. 200.0g PR013443 (Sartomer) is added by a large-bore syringe. 650.0g Genomer4259 (Rahn) is added by a large-bore syringe. The bucket was mixed at 1100 rpm speed (DAC 2800-1000, Flacktek) for 1 minute. The HP-5 solution was poured into the bucket. The bucket was further fast mixed at 1100 rpm for 1 minute.

[0345] Example 3 - Preparation of a base resin formulation containing a photo-switchable photoinitiator

[0346] A stock solution of a photoconvertible photoinitiator is prepared by dissolving the desired photoconversion in a 1:1 v / v mixture of N,N-dimethylacrylamide (DMAA, Rahn) and benzyl acrylate (Beantown chemical) in a 20 mL amber vial so that the final concentration is 1 mg / mL of photoconversion in the solvent. 0.3 mL of this photoconversion stock solution is added to the above 14.7 g base resin to create a resin formulation containing about 20 ppm of photoconversion. At this point, a polymerization enhancer, such as N-methyldiethanolamine, is added at the desired concentration (usually 3 wt %). The resin formulation is rapidly mixed (DAC 2800-1000, Flacktek) at 3000 rpm for 1 minute, twice in total. The formulation is then transferred to a 2.5 mL plastic cuvette (Einmal-Küvetten) and covered with a lid. The sealed cuvette is centrifuged at 4500 rpm for 5 minutes to remove residual bubbles (5804R, Eppendorf).

[0347] Example 4 - Evaluation of Photo-Switchable Photoinitiators in Test Resins

[0348] Formulated under crossed beams of UV and visible illumination

[0349] A centrifuged, bubble-free cuvette containing the resin prepared according to Example 3 and containing 3% N-methyldiethanolamine was placed in a setup featuring two crossed, approximately collimated coherent light sources. In the case of a photo-switchable photoinitiator comprising a naphthopyran molecule or one of its derivatives, the light sources were orthogonal to each other and crossed in the center of a 1 cm x 1 cm square cuvette (405 nm, 170 mW / cm 2 ) and (532nm, 1.6W / cm 2 ) light source. In the case of a photo-switchable photoinitiator comprising a spironaphthoxazine molecule or one of its derivatives, the light source is (405 nm, 0.9 mW / cm 2 ) and (638nm, 2.8W / cm 2 ) light source. The time required for a polymerized spot to form ("voxel time") was recorded and is representative of part formation in the printer. In a separate experiment, the resin was exposed to 405nm light only and the time required for curing ("light sheet time") was recorded. This can be used as a representative of curing from a UV light sheet in the printer. The [voxel / light sheet] times for NO17 and NP31 were [59 seconds / 168 seconds] and [13 seconds / 20 seconds], respectively. Exposure and measurements were performed at room temperature (approximately 22°C).

[0350] In this work, the time difference between voxel formation and photo-sheet curing determined as described in Example 4 is used as a metric for predicting the performance of photo-convertible photo-initiators for volumetric printing in resin formulations, and using wavelengths and power levels that are the same or substantially similar to those described in the Examples. The ratio of (UV light curing time / voxel curing time) is at least 1 (1), where the voxel curing time is 30 seconds or less, and preferably, the ratio of (UV curing time / voxel curing time) is at least 1.2 under the conditions of Example 4 and the voxel curing time is less than 15 seconds, which is useful for screening preferred photo-convertible photo-initiators for volumetric printing.

[0351] Although not wishing to be bound by theory, it is believed that a ratio of (UV light curing time / voxel curing time) of no greater than 1 or a curing time greater than 30 seconds should not be interpreted as indicating that a particular photoconvertible photoinitiator is not suitable for use in volumetric printing. It is expected that such results can be used as an indicator to change one or more printing conditions (e.g., photoconvertible photoinitiator and / or synergist concentration, power level of one or both of the excitation light, printing temperature, and / or one or both of the excitation wavelengths) to obtain better printing suitability. Such adjustments are routine to one of ordinary skill in the art without undue experimentation.

[0352] Example 5 - Example of a procedure for printing an object

[0353] A cuvette of the photohardenable composition (e.g., as described in Example 3) is placed in a plastic holder on a motorized stage. A digital micromirror device (Texas Instruments) is illuminated using a red or green laser (e.g., 638 nm or 532 nm Cw diode laser, 10-40 W operating power) to form a pattern projected into the cuvette along the z-axis to generate approximately 1-10 W / cm 2 UV or ultraviolet light (e.g., 375 nm or 405 nm CW diode laser, 50-300 mW operating power) is used to form a light sheet that passes through the cuvette orthogonally to the projected pattern to illuminate a single xy plane of nominally 100 micron thickness to produce, for example, about 0.1-5 W / cm 2 The stage advances in increments of 1-100 microns at intervals of 50-5000 ms, with the UV or ultraviolet light forming a light sheet and the red or green light pattern changing with each advance, corresponding to a slice of a computer-generated three-dimensional object. In areas exposed to both wavelengths of light simultaneously or nearly simultaneously, the photohardenable composition is hardened. In this way, due to the high zero shear viscosity or yield stress of the non-Newtonian photohardenable composition, a three-dimensional solid object is formed without displacement (e.g., sinking or drifting) and without the need for a support structure or connection to a build platform.

[0354] The light sheet may be constructed by means known in the art, including but not limited to techniques including lasers and Powell lenses, galvanometers, and / or polygon scanning mirrors. Alternatively, one or more LEDs may be used as the light source.

[0355] Information useful in conjunction with the invention disclosed herein includes the x, y, z volume methods described in US Pat. Nos. 4,041,476, 4,078,229, 4,238,840, 4,466,080, 4,471,470, and 4,333,165 to Swainson and US Pat. No. 5,230,986 to Neckers. Other information that may be useful includes International Patent Application No. PCT / US2021 / 035791 filed by Quadratic 3D, Inc. on June 3, 2021, entitled “Volumetric Three-Dimensional Printing Methods Including A Light Sheet And Systems”, and U.S. Patent No. 10,843,410 to Lippert et al., “System And Method For A Three-Dimensional Optical Switch Display (OSD) Device”; and International Patent Application No. PCT / US2022 / 037491 filed by Quadratic 3D, Inc. on July 18, 2022. Each of the foregoing is hereby incorporated herein by reference in its entirety.

[0356] Before forming an object or "printing", a digital file of the object to be printed is obtained. If the digital file is not in a format that can be used to print the object, the digital file is converted into a format that can be used to print the object. An example of a typical format that can be used for printing is an STL file. Typically, the STL file is then sliced ​​into two-dimensional layers using three-dimensional slicer software and converted into G-Code or a set of machine commands, which facilitates the construction of the object. See B. Redwood et al., "The 3D Printing Handbook-Technologies, designs applications", 3D HUBSB.V.2018.

[0357] As used herein, unless otherwise provided, "alkyl" refers to a branched or straight chain fully saturated acyclic aliphatic hydrocarbon group (i.e., composed of carbon and hydrogen, containing no double or triple bonds). Examples include, but are not limited to, alkyl groups having 1 to 20 (more typically 1 to 10) carbon atoms, which may be straight or branched chain alkyl groups.

[0358] As used herein, unless otherwise provided, "alkoxy" refers to a straight or branched chain alkyl moiety covalently bonded to the parent molecule through an -O- linkage. Examples include, but are not limited to, alkoxy groups having 1 to 20 (more typically 1 to 10) carbon atoms, which may be straight chain, branched or cyclic alkoxy groups, examples of which include, but are not limited to, methoxy (MeO), ethoxy (EtO), etc.

[0359] As used herein, unless otherwise provided, "aralkyl" or "arylalkyl" refers to an alkyl moiety substituted with an aryl group. Examples include, but are not limited to, aralkyl groups having 7 to 20 carbon atoms, examples of which include, but are not limited to, benzyl, methylphenyl, ethylphenyl, and the like.

[0360] As used herein, unless otherwise provided, "cycloalkyl" refers to a saturated aliphatic ring system moiety having, for example, 3 to 20 carbon atoms. Examples include, but are not limited to, cyclopropyl, cyclopentyl, cyclohexyl, cycloheptyl, and the like.

[0361] As used herein, unless otherwise provided, "heteroalkyl" refers to an alkyl group containing one or more heteroatoms. When two or more heteroatoms are present, the heteroatoms may be the same or different. Examples of heteroalkyl groups include, but are not limited to, CH2-OH, OC n H .2n+1 , where n is any integer greater than or equal to 1.

[0362] As used herein, unless otherwise provided, "aryloxy" refers to an aryl moiety covalently bonded to the parent molecule through an -O- linkage.

[0363] As used herein, unless otherwise provided, "heteroatom" refers to any atom that is not hydrogen or carbon. Typical heteroatoms include, but are not limited to, S (sulfur), N (nitrogen), O (oxygen), P (phosphorus), Cl (chlorine), Br (bromine), I (iodine), F (fluorine), etc.

[0364] As used herein, unless otherwise provided, "alkenyl" refers to a monovalent straight or branched chain moiety containing a carbon double bond, for example, 2 to 20 carbon atoms. Examples include, but are not limited to, 1-propenyl, 2-propenyl, 2-methyl-1-propenyl, 1-butenyl, 2-butenyl, etc.

[0365] As used herein, unless otherwise provided, "amido" refers to -NRC(=O)R', wherein R and R' may be the same or different, wherein R and R' may independently represent, for example, but not limited to, hydrogen, alkyl, or aryl.

[0366] As used herein, unless otherwise provided, "amino" refers to -NRR', wherein R and R' may independently represent, for example but not limited to, hydrogen, alkyl, or aryl.

[0367] As used herein, unless otherwise provided, "carboxyl ester" refers to -C(=O)O. Examples include groups having a -COOR or -OCOR structure, where R can represent, for example but not limited to, hydrogen, alkyl or aryl.

[0368] As used herein, unless otherwise provided, "carboxy" refers to -COOH.

[0369] As used herein, "carbonyl" refers to C=O, unless otherwise provided.

[0370] As used herein, unless otherwise provided, "aryl" refers to any aromatic carbocyclic or heterocyclic group containing unsaturated C-C bonds conjugated to each other, whether one ring or multiple fused rings. Examples of aryl groups include, but are not limited to, aryl groups containing, for example, 5 to 20 carbon atoms, examples of which include, but are not limited to, phenyl, naphthyl, phenanthrenyl, and the like. Examples of "aryl" substituents include, but are not limited to, phenyl, naphthyl, anthracenyl, indenyl (naphthacenyl), fluorenyl, pyrenyl, and the like, or any aromatic heterocyclic group such as pyridine, pyrazine, indole, purine, furan, thiophene, pyrrole, and the like.

[0371] As used herein, unless otherwise provided, "heteroaryl" may also refer to an aromatic ring system portion in which one or more ring atoms are heteroatoms, whether one ring or multiple fused rings. When there are two or more heteroatoms, the heteroatoms may be the same or different. In a fused ring system, one or more heteroatoms may be present only in one of the rings. Examples of heteroaryl include, but are not limited to, benzothiazolyl, benzoxazolyl, quinazolinyl, quinolyl, isoquinolyl, quinoxalinyl, pyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, pyrrolyl, oxazolyl, indolyl, thiazolyl, etc.

[0372] As used herein, unless otherwise provided, a "substituted" group, part or molecule refers to a group, part or molecule having at least one hydrogen replaced by a group of atoms or non-hydrogen atoms. (A group of atoms or non-hydrogen atoms replacing hydrogen is also generally referred to as a substituent) When substituted, a substituent is one or more groups selected individually and independently. Examples of various substituents include but are not limited to alkyl, cycloalkyl, alkenyl, cycloalkenyl, ether, aryl, heteroaryl, heterocycloalkyl, hydroxyl, oxy, alkoxy, ester, thioester, acyl, carboxyl, carbonyl, cyano, nitro, amino, amide, halogen (e.g., fluorine, chlorine, bromine, iodine) or sulfur. When a substituent includes more than one substituent, the substituent may be bonded to the same atom or two or more different atoms in the group. A substituent comprising a group of atoms may also be optionally substituted.

[0373] When used as a feature of a portion of a container or build chamber, "optically transparent" means having high optical transmittance for the wavelength of light used, and "optically flat" means not distorted (e.g., optical wavefronts entering the portion of the container or build chamber remain largely unaffected).

[0374] As used herein, the singular forms "a", "an" and "the" include pluralities unless the context clearly dictates otherwise. Thus, for example, reference to a light-emitting material includes reference to one or more (one or more) of such materials.

[0375] The applicant has introduced the full content of all patents, patent applications, publications and other references of all quotations or references in the present disclosure in particular. Further, when the list of equivalent, concentration or other values ​​or parameters is provided as scope, preferred range or high preferred value and low preferred value, this should be understood as particularly disclosing all scopes formed from any high range limit or high preferred value and any low range limit or low preferred value, no matter whether scope is disclosed individually. In the case of the scope of numerical value enumerated herein, unless otherwise indicated, the scope is intended to include all integers and fractions in its endpoint and the scope, and the upper limit and lower limit of each scope. It is not expected that the scope of the present invention is limited to the specified value when limiting the scope.

[0376] Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein.It is intended that the specification and examples be considered exemplary only, with the following claims and their equivalents indicating the true scope and spirit of the invention.

Claims

1. A photo-switchable photoinitiator comprising a photochromic benzospiropyran molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety represented by the general formula (I): Ar 1 -C(=O)-C(=O)-Ar 2 (I) Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

2. The photo-switchable photoinitiator according to claim 1, wherein the benzospiropyran molecule is represented by the general formula (II): Where R 1 -R 13 are the same or different, and independently represent, for example, hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkylaryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted ester group, a substituted or unsubstituted carbonate or salt group, a substituted or unsubstituted keto group, a substituted or unsubstituted aldehyde group, a substituted or unsubstituted imino group, a substituted or unsubstituted carboxyl group, a substituted or unsubstituted amide group, a substituted or unsubstituted carbamate group, a substituted or unsubstituted urea group, a substituted or unsubstituted tetrazine group, a substituted or unsubstituted amino group, an iodine group, a bromine group, a chlorine group, a fluorine group, a cyano group, a nitro group, a hydroxyl group, a thiol group, an alkyl thioether group, an aryl thioether group, or a substituted or unsubstituted alcohol group, and Where R 1 -R 13 At least one of the compounds comprises a substituted or unsubstituted α-diketone moiety. 3 . The photo-switchable photoinitiator according to claim 1 , wherein the substituted or unsubstituted α-diketone moiety is linked to the photochromic benzospiropyran molecule through a bond.

4. The photo-switchable photoinitiator of claim 1, wherein the substituted or unsubstituted α-diketone moiety is attached to the photochromic benzospiropyran molecule via a bond to a substituent on the photochromic molecule.

5. The photo-switchable photoinitiator according to claim 1, wherein Ar 1 and Ar 2 The substituted or unsubstituted aryl groups contained in each are the same or different and independently contain an aromatic ring including but not limited to a benzene ring, a naphthalene ring, an anthracene ring, an indene ring, a fluorene ring, etc., wherein the aryl group is substituted or unsubstituted.

6. The photo-switchable photoinitiator according to claim 1, wherein Ar 1 and Ar 2 The substituted or unsubstituted heteroaryl groups contained in each are the same or different and independently contain heteroaryl rings, which include but are not limited to furan rings, thiophene rings, pyrrole rings, oxazole rings, isoxazole rings, thiazole rings, isothiazole rings, imidazole rings, pyrazole rings, pyran rings, pyridine rings, pyrazine rings, indole rings, quinoline rings, isoquinoline rings, xanthene rings, carbazole rings, acridine rings, indoline rings, julolidine rings, etc., wherein the heteroaryl groups are substituted or unsubstituted.

7. The photo-switchable photoinitiator according to claim 1, wherein the substituents on the aryl and / or heteroaryl groups comprise halogen atoms, alkyl groups, alkoxy groups, alkylamino groups, dialkylamino groups, alkylthio groups, heterocyclic groups, more specifically, hydrogen atoms, methyl groups, ethyl groups, isopropyl groups, tert-butyl groups, phenyl groups, trifluoromethyl groups, cyano groups, acetyl groups, ethoxycarbonyl groups, carboxyl groups, carboxyl groups, amino groups, methylamino groups, dimethylamino groups, ethylamino groups, diethylamino groups, isopropylamino groups, diisopropylamino groups, cyclohexylamino groups, dicyclohexylamino groups, acetylamino groups, piperidinyl groups, pyrrolidinyl groups, --PO3 groups H, methoxy, ethoxy, propoxy, isopropoxy, butoxy, pentyloxy, phenoxy, hydroxyl, acetoxy, methylthio, ethylthio, isopropylthio, mercapto, acetylthio, thiocyano, methylsulfinyl, methylsulfonyl, dimesylsulfonyl, sulfonate or salt group, fluorine atom, chlorine atom, bromine atom, iodine atom, trimethylsilyl, triethylsilyl, furyl, thienyl, pyridyl, piperidyl, morpholino, pyrrolidinyl and the like.

8. The photo-switchable photoinitiator of claim 1, wherein the α-diketone moiety comprises a substituted or unsubstituted benzil group.

9. The photo-switchable photoinitiator of claim 2, wherein the α-diketone moiety comprises a substituted or unsubstituted benzil group.

10. The photo-switchable photoinitiator according to claim 2, wherein the α-diketone moiety is contained in R 1 -R 13 At least one of them as its connection.

11. The photo-switchable photoinitiator according to claim 2, wherein any two adjacent R 1 To R 13 The group represents the atoms necessary to complete the ring structure linking together two adjacent groups, the ring structure comprising at least one substituted or unsubstituted α-diketone moiety represented by the general formula (I) linked thereto.

12. A photo-switchable photoinitiator comprising a photochromic naphthopyran molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety represented by the general formula (I): Ar 1 -C(=O)-C(=O)-Ar 2 (I) Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

13. The photo-switchable photoinitiator according to claim 12, wherein the naphthopyran molecule is represented by the general formula (III): Where R a , R b and R 1 -R 8 are the same or different, and represent, for example, hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkylaryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted ester group, a substituted or unsubstituted carbonate group, a substituted or unsubstituted keto group, a substituted or unsubstituted aldehyde group, a substituted or unsubstituted imino group, a substituted or unsubstituted carboxyl group, a substituted or unsubstituted amide group, a substituted or unsubstituted carbamate group, a substituted or unsubstituted urea group, a substituted or unsubstituted tetrazine group, a substituted or unsubstituted amino group, an iodine group, a bromine group, a chlorine group, a fluorine group, a cyano group, a nitro group, a hydroxyl group, a thiol group, an alkyl thioether group, an aryl thioether group, or a substituted or unsubstituted alcohol group, and Where R a , R b and R 1 -R 8 At least one of the compounds comprises a substituted or unsubstituted α-diketone moiety.

14. The photo-switchable photoinitiator according to claim 12, wherein the naphthopyran molecule is represented by the general formula (IV): Where R a , R b and R 1 -R 8 are the same or different, and represent, for example, hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkylaryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted ester group, a substituted or unsubstituted carbonate group, a substituted or unsubstituted keto group, a substituted or unsubstituted aldehyde group, a substituted or unsubstituted imino group, a substituted or unsubstituted carboxyl group, a substituted or unsubstituted amide group, a substituted or unsubstituted carbamate group, a substituted or unsubstituted urea group, a substituted or unsubstituted tetrazine group, a substituted or unsubstituted amino group, an iodine group, a bromine group, a chlorine group, a fluorine group, a cyano group, a nitro group, a hydroxyl group, a thiol group, an alkyl thioether group, an aryl thioether group, or a substituted or unsubstituted alcohol group, and Where R a , R b and R 1 -R 8 At least one of the compounds comprises a substituted or unsubstituted α-diketone moiety.

15. The photo-switchable photoinitiator of claim 12, wherein the substituted or unsubstituted α-diketone moiety is attached to the photochromic naphthopyran molecule through a bond.

16. The photo-switchable photoinitiator of claim 12, wherein the substituted or unsubstituted α-diketone moiety is attached to the photochromic molecule through a bond to a substituent on the photochromic molecule.

17. The photo-switchable photoinitiator according to claim 12, wherein Ar 1 and Ar 2 The substituted or unsubstituted aryl groups contained in each are the same or different and independently contain an aromatic ring including but not limited to a benzene ring, a naphthalene ring, an anthracene ring, an indene ring, a fluorene ring, etc., wherein the aryl group is substituted or unsubstituted.

18. The photo-switchable photoinitiator according to claim 12, wherein Ar 1 and Ar 2 The substituted or unsubstituted heteroaryl groups contained in each are the same or different and independently contain heteroaryl rings, which include but are not limited to furan rings, thiophene rings, pyrrole rings, oxazole rings, isoxazole rings, thiazole rings, isothiazole rings, imidazole rings, pyrazole rings, pyran rings, pyridine rings, pyrazine rings, indole rings, quinoline rings, isoquinoline rings, xanthene rings, carbazole rings, acridine rings, indoline rings, julolidine rings, etc., wherein the heteroaryl groups are substituted or unsubstituted.

19. The photo-switchable photoinitiator according to claim 12, wherein the substituents on the aryl and / or heteroaryl groups comprise halogen atoms, alkyl groups, alkoxy groups, alkylamino groups, dialkylamino groups, alkylthio groups, heterocyclic groups, more specifically, hydrogen atoms, methyl groups, ethyl groups, isopropyl groups, tert-butyl groups, phenyl groups, trifluoromethyl groups, cyano groups, acetyl groups, ethoxycarbonyl groups, carboxyl groups, carboxyl groups, amino groups, methylamino groups, dimethylamino groups, ethylamino groups, diethylamino groups, isopropylamino groups, diisopropylamino groups, cyclohexylamino groups, dicyclohexylamino groups, acetylamino groups, piperidinyl groups, pyrrolidinyl groups, --PO3 groups H, methoxy, ethoxy, propoxy, isopropoxy, butoxy, pentyloxy, phenoxy, hydroxyl, acetoxy, methylthio, ethylthio, isopropylthio, mercapto, acetylthio, thiocyano, methylsulfinyl, methylsulfonyl, dimesylsulfonyl, sulfonate or salt group, fluorine atom, chlorine atom, bromine atom, iodine atom, trimethylsilyl, triethylsilyl, furyl, thienyl, pyridyl, piperidyl, morpholino, pyrrolidinyl and the like.

20. The photo-switchable photoinitiator of claim 12, wherein the α-diketone moiety comprises a substituted or unsubstituted benzil group.

21. The photo-switchable photoinitiator according to claim 13 or 14, wherein the substituted or unsubstituted α-diketone moiety is attached to an atom contained in the naphthopyran molecule through a bond.

22. The photo-switchable photoinitiator according to claim 13 or 14, wherein the substituted or unsubstituted α-diketone moiety is contained in R a , R b and R 1 -R 8 At least one of them as its connection.

23. The photo-switchable photoinitiator according to claim 13 or 14, wherein the substituted or unsubstituted α-diketone moiety comprises a substituted or unsubstituted benzil group.

24. The photo-switchable photoinitiator according to claim 13 or 14, wherein R a and R b At least one of contains an aryl group or a heteroaryl group.

25. The photo-switchable photoinitiator according to claim 13 or 14, wherein R a and R b At least one of the moieties comprises a phenyl group having attached thereto a substituted or unsubstituted α-diketone moiety.

26. The photo-switchable photoinitiator according to claim 13 or 14, wherein any two adjacent R a , R b , R 1 To R 8 The radical represents the atoms necessary to complete a ring structure linking two adjacent radicals together, said ring structure comprising one or more substituted or unsubstituted α-diketone moieties attached thereto.

27. The photo-switchable photoinitiator according to claim 12 or 13, which is represented by the general formula IIIA:

28. A photo-switchable photoinitiator comprising a photochromic spironaphthoxazine molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety represented by the general formula (I): Ar 1 -C(=O)-C(=O)-Ar 2 (I) Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

29. The photo-switchable photoinitiator according to claim 28, wherein the spironaphthoxazine molecule is represented by the general formula (V): Where R 1 -R 14 are the same or different, and represent, for example, hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkylaryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted ester group, a substituted or unsubstituted carbonate or salt group, a substituted or unsubstituted keto group, a substituted or unsubstituted aldehyde group, a substituted or unsubstituted imino group, a substituted or unsubstituted carboxyl group, a substituted or unsubstituted amide group, a substituted or unsubstituted carbamate group, a substituted or unsubstituted urea group, a substituted or unsubstituted tetrazine group, a substituted or unsubstituted amino group, an iodine group, a bromine group, a chlorine group, a fluorine group, a cyano group, a nitro group, a hydroxyl group, a thiol group, an alkyl thioether group, an aryl thioether group, or a substituted or unsubstituted alcohol group; Where R 1 -R 14 At least one of the compounds comprises a substituted or unsubstituted α-diketone moiety.

30. The photo-switchable photoinitiator according to claim 28, wherein the spironaphthoxazine molecule is represented by the general formula (VI): Where R 1 -R 14 are the same or different, and represent, for example, hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a substituted or unsubstituted alkylaryl group, a substituted or unsubstituted heteroaryl group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted ester group, a substituted or unsubstituted carbonate or salt group, a substituted or unsubstituted keto group, a substituted or unsubstituted aldehyde group, a substituted or unsubstituted imino group, a substituted or unsubstituted carboxyl group, a substituted or unsubstituted amide group, a substituted or unsubstituted carbamate group, a substituted or unsubstituted urea group, a substituted or unsubstituted tetrazine group, a substituted or unsubstituted amino group, an iodine group, a bromine group, a chlorine group, a fluorine group, a cyano group, a nitro group, a hydroxyl group, a thiol group, an alkyl thioether group, an aryl thioether group, or a substituted or unsubstituted alcohol group; Where R 1 -R 14 At least one of the compounds comprises a substituted or unsubstituted α-diketone moiety.

31. The photo-switchable photoinitiator of claim 28, wherein the substituted or unsubstituted α-diketone moiety is attached to the photochromic molecule through a bond.

32. The photo-switchable photoinitiator of claim 28, wherein the substituted or unsubstituted α-diketone moiety is attached to the photochromic molecule through a bond to a substituent on the photochromic molecule.

33. The photo-switchable photoinitiator according to claim 28, wherein Ar 1 and Ar 2 The substituted or unsubstituted aryl groups contained in each are the same or different and independently contain an aromatic ring including but not limited to a benzene ring, a naphthalene ring, an anthracene ring, an indene ring, a fluorene ring, etc., wherein the aryl group is substituted or unsubstituted.

34. The photo-switchable photoinitiator according to claim 28, wherein Ar 1 and Ar 2 The substituted or unsubstituted heteroaryl groups contained in each are the same or different and independently contain heteroaryl rings, which include but are not limited to furan rings, thiophene rings, pyrrole rings, oxazole rings, isoxazole rings, thiazole rings, isothiazole rings, imidazole rings, pyrazole rings, pyran rings, pyridine rings, pyrazine rings, indole rings, quinoline rings, isoquinoline rings, xanthene rings, carbazole rings, acridine rings, indoline rings, julolidine rings, etc., wherein the heteroaryl groups are substituted or unsubstituted.

35. The photo-switchable photoinitiator according to claim 28, wherein the substituents on the aryl and / or heteroaryl groups comprise halogen atoms, alkyl groups, alkoxy groups, alkylamino groups, dialkylamino groups, alkylthio groups, heterocyclic groups, more specifically, hydrogen atoms, methyl groups, ethyl groups, isopropyl groups, tert-butyl groups, phenyl groups, trifluoromethyl groups, cyano groups, acetyl groups, ethoxycarbonyl groups, carboxyl groups, carboxyl groups, amino groups, methylamino groups, dimethylamino groups, ethylamino groups, diethylamino groups, isopropylamino groups, diisopropylamino groups, cyclohexylamino groups, dicyclohexylamino groups, acetylamino groups, piperidinyl groups, pyrrolidinyl groups, --PO3 groups H, methoxy, ethoxy, propoxy, isopropoxy, butoxy, pentyloxy, phenoxy, hydroxyl, acetoxy, methylthio, ethylthio, isopropylthio, mercapto, acetylthio, thiocyano, methylsulfinyl, methylsulfonyl, dimesylsulfonyl, sulfonate or salt group, fluorine atom, chlorine atom, bromine atom, iodine atom, trimethylsilyl, triethylsilyl, furyl, thienyl, pyridyl, piperidyl, morpholino, pyrrolidinyl and the like.

36. The photo-switchable photoinitiator of claim 28, wherein the α-diketone moiety comprises a substituted or unsubstituted benzil group.

37. The photo-switchable photoinitiator according to claim 29 or 30, wherein the substituted or unsubstituted α-diketone moiety is attached to an atom contained in the spironaphthoxazine molecule through a bond.

38. The photo-switchable photoinitiator according to claim 29 or 30, wherein the substituted or unsubstituted α-diketone moiety is contained in R 1 -R 14 At least one of them as its connection.

39. The photo-switchable photoinitiator of claim 29 or 30, wherein the substituted or unsubstituted α-diketone moiety comprises a substituted or unsubstituted benzil group.

40. The photo-switchable photoinitiator according to claim 29 or 30, wherein R 1 -R 14 At least one of contains an aryl group or a heteroaryl group.

41. The photo-switchable photoinitiator according to claim 29 or 30, wherein R 1 -R 14 At least one of the groups comprises a phenyl group.

42. The photo-switchable photoinitiator according to claim 29 or 30, wherein R 1 -R 14 At least one of the moieties comprises a phenyl group having attached thereto a substituted or unsubstituted α-diketone moiety.

43. The photo-switchable photoinitiator according to claim 29 or 30, wherein any two adjacent R 1 -R 14 The radical represents the atoms necessary to complete a ring structure linking two adjacent radicals together, said ring structure comprising one or more substituted or unsubstituted α-diketone moieties attached thereto.

44. The photo-switchable photoinitiator according to claim 28 or 29, which is represented by formula VA:

45. The photo-switchable photoinitiator according to claim 29, wherein R 1 represents a substituted or unsubstituted alkyl or aryl group (eg, benzyl, ie, a benzene ring with an attached CH2 group).

46. ​​The photo-switchable photoinitiator according to claim 29, wherein R 7 represents a substituted or unsubstituted α-diketone moiety.

47. The photo-switchable photoinitiator according to claim 45, wherein R 7 represents a substituted or unsubstituted α-diketone moiety.

48. The photo-switchable photoinitiator according to claim 30, wherein R 1 represents a substituted or unsubstituted alkyl or aryl group (eg, benzyl, ie, a benzene ring with an attached CH2 group).

49. The photo-switchable photoinitiator according to claim 30, wherein R 7 represents a substituted or unsubstituted α-diketone moiety.

50. The photo-switchable photoinitiator of claim 48, wherein R 7 represents a substituted or unsubstituted α-diketone moiety.

51. A photohardenable composition comprising a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator can be activated by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component at the intersection of the two wavelengths of light, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photochromic molecule, the photochromic molecule comprises a benzospiropyran molecule, the benzospiropyran molecule comprises one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety represented by the general formula (I): Ar 1 -C(=O)-C(=O)-Ar 2 (I) Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

52. A photohardenable composition comprising a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator can be activated by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component at the intersection of the two wavelengths of light, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photochromic molecule, the photochromic molecule comprises a naphthopyran molecule, the naphthopyran molecule comprises one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety represented by the general formula (I): Ar 1 -C(=O)-C(=O)-Ar 2 (I) Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

53. A photohardenable composition comprising a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator is activatable by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component at the intersection of the two wavelengths of light, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photochromic molecule comprising a spironaphthooxazine molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety represented by the general formula (I): Ar 1 -C(=O)-C(=O)-Ar 2 (I) Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

54. The photohardenable composition of any one of claims 51-53, further comprising one or more co-initiators.

55. The photohardenable composition of any one of claims 51-53, further comprising one or more sensitizers.

56. The photohardenable composition of claim 54, further comprising one or more sensitizers.

57. The photohardenable composition of any one of claims 51-53, wherein the photohardenable resin component exhibits non-Newtonian rheological behavior.

58. The photohardenable composition of claim 54, wherein the co-initiator comprises a tertiary amine.

59. The photohardenable composition of claim 54, wherein the co-initiator comprises a borate.

60. The photohardenable composition of claim 54, wherein the co-initiator comprises an iodonium salt.

61. The photohardenable composition of claim 54, wherein the co-initiator comprises a combination of a borate and an iodonium salt.

62. The photohardenable composition of claim 54, wherein the co-initiator comprises a combination of a tertiary amine and an iodonium salt.

63. The photohardenable composition of claim 55, wherein the sensitizer comprises isopropylthioxanthone or Esacure 3644.

64. The photohardenable composition of any one of claims 51-53, wherein the composition further comprises a thermally activated free radical initiator.

65. The photohardenable composition of any one of claims 51-53, further comprising a second light-activated photoinitiator, wherein the photoinitiator is not significantly activated by light of the first and second wavelengths.

66. The photohardenable composition of any one of claims 51-53, wherein the photohardenable composition exhibits non-Newtonian rheological behavior.

67. A hardenable resin composition useful for forming an object, the hardenable resin composition comprising: (i) the photohardenable composition of any one of claims 51-53; and (ii) a resin component hardenable by a thermally driven reaction or mechanism, the resin component comprising a monomer, an oligomer, a prepolymer, a polymer, or a mixture comprising at least one of the foregoing, wherein the photohardenable composition comprises a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator is activatable by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component at the intersection of the two wavelengths of light, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photochromic molecule, the photochromic molecule comprising one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule, or a spironaphthooxazine molecule, and wherein the substituted or unsubstituted α-diketone moiety is represented by the general formula (I): Ar 1 -C(=O)-C(=O)-Ar 2 (I) Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl.

68. The hardenable resin composition of claim 67, wherein the hardenable resin composition exhibits non-Newtonian rheological behavior.

69. The hardenable resin composition of claim 67, wherein the composition further comprises a thermally activated free radical initiator.

70. The hardenable resin composition of claim 67, wherein the composition further comprises a thermally activated free radical initiator.

71. A method of forming an object, comprising: (a) providing a volume containing a photohardenable composition, wherein the photohardenable composition comprises a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator is activatable by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component at the intersection of the two wavelengths of light, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photochromic molecule, wherein the photochromic molecule comprises a benzospiropyran molecule, wherein the benzospiropyran molecule comprises one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety represented by the general formula (I): Ar 1 -C(=O)-C(=O)-Ar 2 (I) Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl; (b) irradiating one or more selected locations within the volume of the photohardenable composition with light having a first wavelength and light having a second wavelength simultaneously or sequentially, wherein the light having the first wavelength and the light having the second wavelength activate the photoconvertible photoinitiator at the one or more selected locations to induce a crosslinking or polymerization reaction in the photohardenable composition at the intersection of the first and second wavelengths at the one or more selected locations within the volume to at least partially form an object; and (c) optionally repeating step b) irradiating the photohardenable composition at one or more of the same or different selected locations in the volume until the object is partially or completely formed.

72. A method of forming an object, comprising: (a) providing a volume of a hardenable resin composition, wherein the hardenable resin comprises (i) a photohardenable composition; and (ii) a resin component that can be hardened by a heat-driven reaction or mechanism, the resin component comprising a monomer, an oligomer, a prepolymer, a polymer, or a mixture comprising at least one of the foregoing, wherein the photohardenable composition comprises a photohardenable resin component and a photoconvertible photoinitiator, wherein the photoconvertible photoinitiator can be activated by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component at the intersection of the two wavelengths of light, wherein the first wavelength and the second wavelength are different, and wherein the photoconvertible photoinitiator comprises a photochromic molecule, the photochromic molecule comprises one or more substituents, wherein at least one substituent comprises a substituted or unsubstituted α-diketone moiety, wherein the photochromic molecule comprises a benzospiropyran molecule, a naphthopyran molecule, or a spironaphthooxazine molecule, and wherein the substituted or unsubstituted α-diketone moiety is represented by the general formula (I): Ar 1 -C(=O)-C(=O)-Ar 2 (I) Among them, Ar 1 and Ar 2 are the same or different and are independently substituted or unsubstituted aryl or substituted or unsubstituted heteroaryl; (b) forming an intermediate object from the hardenable resin composition, wherein the forming of the intermediate object comprises: (i) irradiating one or more selected locations within the volume of the hardenable resin composition with light having a first wavelength and light having a second wavelength simultaneously or sequentially, wherein the light having the first wavelength and the light having the second wavelength activate the photo-switchable photoinitiator at the one or more selected locations to induce a crosslinking or polymerization reaction in the photohardenable composition at the intersection of the first and second wavelengths at the one or more selected locations within the volume to at least partially form an object; and (ii) optionally repeating step (i) at one or more of the same or different selected locations within the volume of the hardenable resin composition until an intermediate object is formed; and (c) hardening (e.g., further reacting, further polymerizing, further chain extending) the resin components in the intermediate object through a heat-driven reaction or mechanism to form the object.

73. The method of claim 71, wherein the photohardenable composition exhibits non-Newtonian rheological behavior.

74. The method of claim 71, wherein the photohardenable composition further comprises a thermally activated free radical initiator.

75. The method of claim 72, wherein the hardenable resin composition exhibits non-Newtonian rheological behavior.

76. The method of claim 72, wherein the hardenable resin composition further comprises a thermally activated free radical initiator.

77. A method according to claim 71, wherein the photohardenable composition further comprises a photoinitiator, wherein the photoinitiator is not significantly activated by light of the first wavelength and the second wavelength, and wherein the method further comprises a post-curing step, the post-curing step comprising exposing the object to light of a third wavelength to further harden the object, the third wavelength being different from the first and second wavelengths.

78. A method according to claim 72, wherein the photohardenable composition further comprises a photoinitiator, wherein the photoinitiator is not significantly activated by light of the first wavelength and the second wavelength, and wherein the method further comprises a post-curing step, the post-curing step comprising exposing the object to light of a third wavelength to further harden the object, the third wavelength being different from the first and second wavelengths.

79. The method of claim 71, wherein the third wavelength is in the ultraviolet wavelength range.

80. The method of claim 72, wherein the third wavelength is in the ultraviolet wavelength range.

81. A method according to claim 71, wherein the photoconvertible photoinitiator can be activated by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component, wherein the first and second wavelengths are different, and wherein the first wavelength is in the range of about 300 to about 550 nm and the second wavelength is in the range of about 450 to about 1000 nm.

82. A method according to claim 72, wherein the photoconvertible photoinitiator can be activated by exposure to light having a first wavelength and light having a second wavelength to induce a crosslinking or polymerization reaction in the photohardenable resin component, wherein the first and second wavelengths are different, and wherein the first wavelength is in the range of about 300 to about 550 nm and the second wavelength is in the range of about 450 to about 1000 nm.

83. The method of claim 81, wherein the first wavelength is in the range of about 350 to about 460 nm and the second wavelength is in the range of about 450 to about 700 nm.

84. The method of claim 82, wherein the first wavelength is in the range of about 350 to about 460 nm and the second wavelength is in the range of about 450 to about 700 nm.

85. The method of claim 81, wherein the first wavelength is in the range of about 350 to about 410 nm and the second wavelength is in the range of about 450 to about 700 nm.

86. The method of claim 82, wherein the first wavelength is in the range of about 350 to about 410 nm and the second wavelength is in the range of about 450 to about 700 nm.

87. The method of claim 71, wherein the power density of the first wavelength light at the one or more selected locations is between about 0.01 and about 100,000 W / cm 2 and the power density of the second wavelength light at the one or more selected locations is between about 0.01 and about 100,000 W / cm 2 within the range.

88. The method of claim 72, wherein the power density of the first wavelength light at the one or more selected locations is between about 0.01 and about 100,000 W / cm 2 and the power density of the second wavelength light at the one or more selected locations is between about 0.01 and about 100,000 W / cm 2 within the range.

89. The method of claim 71, wherein the exposure energy of the first wavelength light at the one or more selected locations is between about 0.001 and about 1,000 mJ / cm 2 and the exposure energy of the second wavelength light at the one or more selected locations is between about 0.01 and about 100,000 mJ / cm 2 within the range.

90. The method of claim 72, wherein the exposure energy of the first wavelength light at the one or more selected locations is between about 0.001 and about 1,000 mJ / cm 2 and the exposure energy of the second wavelength light at the one or more selected locations is between about 0.01 and about 100,000 mJ / cm 2 within the range.

91. A method according to claim 71, wherein the amount of time for which one or more selected locations within the volume are simultaneously or sequentially exposed to the first wavelength of light and the second wavelength of light to induce crosslinking or polymerization of the photohardenable composition at the one or more selected locations is insufficient to cause hardening of the photohardenable composition when only one of the first and second wavelengths is present.

92. A method according to claim 72, wherein the amount of time for which one or more selected locations within the volume are simultaneously or sequentially exposed to the first wavelength of light and the second wavelength of light to induce crosslinking or polymerization of the photohardenable composition at the one or more selected locations is insufficient to cause hardening of the photohardenable composition when only one of the first and second wavelengths is present.

93. The method of claim 71 , wherein the first wavelength of light and the second wavelength of light are projected into the volume as separate optical projections.

94. The method of claim 72, wherein the first wavelength of light and the second wavelength of light are projected into the volume as separate optical projections.

95. The method of claim 93, wherein the projecting of the first wavelength of light comprises a light sheet.

96. The method of claim 94, wherein the projecting of the first wavelength of light comprises a light sheet.

97. The method of claim 93, wherein the projection of light at the second wavelength comprises an optical image.

98. The method of claim 94, wherein the projection of light at the second wavelength comprises an optical image.

99. The method of claim 97, wherein the projection of light at the second wavelength comprises an optical image.

100. The method of claim 98, wherein the projection of light at the second wavelength comprises an optical image.

101. The method of claim 99, wherein a projection direction of the light sheet is orthogonal to a projection direction of the optical image, which is orthogonal to the projection direction thereof such that the light sheet and the optical image intersect in a common plane.

102. The method of claim 100, wherein a projection direction of the light sheet is orthogonal to a projection direction of the optical image, which is orthogonal to the projection direction thereof such that the light sheet and the optical image intersect in a common plane.

103. The method of claim 71, wherein the object at least partially formed in the photohardenable composition is maintained in a fixed position or minimally displaced in the unhardened photohardenable composition during formation.

104. The method of claim 72, wherein the object at least partially formed in the photohardenable composition is maintained in a fixed position or minimally displaced in the unhardened photohardenable composition during formation.

105. New, useful and non-obvious processes, machines, articles of manufacture and compositions of matter as herein shown and described.

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