Photocurable composition for multi-material 3D printing

Abstract

Photocurable compositions are described herein. The photocurable composition includes a hybrid monomer, a photoradical generator, and a photoacid generator. The hybrid monomer includes a free radically polymerizable group and a cationically polymerizable group. The photoradical generator and the photoacid generator are selected such that at least one of the photoradical generator and the photoacid generator absorbs a wavelength of light which the other does not. The photocurable composition is particularly useful for providing cured products. A method for the manufacture of a multi-material cured composition derived from the photocurable composition is also described.

Description

PHOTOCURABLE COMPOSITION FOR MULTI-MATERIAL 3D PRINTINGCROSS-REFERENCE TO RELATED APPLICATIONThis application claims priority to and the benefit of U.S. Provisional Application No. 63 / 529,534, filed on July 28, 2023, the contents of which is hereby incorporated by reference in its entirety.FEDERAL RESEARCH STATEMENT

[0001] This invention was made with government support under Grant no. DGE1610403 awarded by the National Science Foundation and Grant no. W911NF-22-1-0115 awarded by the Army Research Office. The government has certain rights in the invention.BACKGROUND

[0002] Multi-material three-dimensional (3D) printing is an attractive tool for the expansion of the utility of additive nanomanufacturing. When compared to single material methods, it offers the ability to reduce printing time for complicated structures. It also gives access to metamaterials in a single step, not feasible from single material printing without complicated and specialized printing equipment. Recent demonstrations of multi-material printing through multi-nozzle extrusion-based methods demonstrate the utility, however suffer from a lack of both resolution and speed offered by photolithography-based printing. However, the use of single resin feedstocks to produce multi-materials is a challenge as careful control over multiple chemistries simultaneously is needed.

[0003] Accordingly, it would be advantageous to provide new materials for multi-material 3D printing that can overcome the above-described technical limitations of existing processes. It would be particularly useful to provide a method for wavelength- selective photopolymerization of a single resin for multi-material printing in one pot.SUMMARY

[0004] An aspect of the present disclosure is a photocurable composition comprising: a hybrid monomer comprising a free radically polymerizable group and a cationically polymerizable group; a photoradical generator; and a photoacid generator; wherein the photoradical generator absorbs light in at least one spectral region that does not substantially overlap with an absorption of the photoacid generator; or the photoacid generator absorbs light in at least one spectral region that does not substantially overlap with an absorption of thephotoradical generator; or both the photoradical generator and the photoacid generator absorb light in spectral regions that do not substantially overlap.

[0005] Another aspect is a cured product provided by polymerization of the photocurable composition.

[0006] Another aspect is a method for the manufacture of a multi-material composition, the method comprising: irradiating the photocurable composition with a first wavelength of light, wherein the first wavelength of light is selected to activate the photoradical generator to initiate polymerization of the free radically polymerizable group of the hybrid monomer and to activate the photoacid generator to initiate polymerization of the cationically polymerizable group to provide a first domain; and irradiating the photocurable composition with a second wavelength of light, wherein the second wavelength of light is selected to activate the photoradical generator to initiate polymerization of the free radically polymerizable group of the hybrid monomer to provide a second domain; wherein the first domain is coupled to the second domain at an interface between the first domain and the second domain; wherein the first domain has an elastic modulus that is greater than an elastic modulus of the second domain; and wherein the second domain has a strain at break that is greater than a strain at break for the first domain.

[0007] The above described and other features are exemplified by the following figures and detailed description.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The following figures are exemplary embodiments.

[0009] FIG. 1 is a schematic illustration of a two color resin printer for use with the photocurable composition described herein.

[0010] FIG. 2 shows illustrative chemical structures of monomers and schematic illustrations showing the formation of disparate networks upon exposure to UV and violet LEDs according to an aspect of the disclosure.

[0011] FIG. 3 shows chemical structures of an exemplary radical initiator, photoacid generator, and photosensitizer and normalized absorbance profiles for photosystem components (solid black lines) and LED emission profiles (dashed lines), with shaded spectral regions showing overlap between them.

[0012] FIG. 4 shows real-time Fourier transform infrared (RT-FTIR) characterization of acrylate (C=C, 3100 cm ) conversion for hybrid resin using the following composition: (3,4- epoxycyclohexyl)methyl acrylate (ECA) (67.9 mole percent (mol%)), phenylbis(2,4,6- trimethylbenzoyl)phosphine oxide (BAPO) (0.5 mol%), bis [4-(diphenylsulfonio)phenyl] sulfide bis(hexafluoroantimonate) (THS) (1 mol%), 3,6-dimethoxy-9H-thioxanthen-9-one (MeOTX) (0.5mol%), 2-hydroxyethyl acrylate (HEA) (30 mol%), and tetra(ethylene glycol) diacrylate (TEGDA) (0.1 mol%).

[0013] FTG. 5 shows RT-FTIR characterization of epoxy (C-O-C, 3915 cm1) conversion for acrylate-free proxy resin using the following composition: 3,4-epoxycyclohexylmethyl 3,4- epoxycyclohexanecarboxylate (ECC) (58.5 mol%), THS (1 mol%), MeOTX (0.5 mol%), 3-ethyl- 3-oxetanemethanol (OXA) (40 mol%), with resin samples having a 50 pm thickness and beginning irradiation approximately 9 seconds after starting the measurement using an LED intensity of 10 mW / cm2. Dashed lines represent a rolling average.

[0014] FIG. 6 shows representative stress-strain curves for hard (UV light) and soft (violet light) dogbones, with pictures as insets (Ixwxh dimensions = 20x4x0.5 mm3). Soft samples were washed with acetone (solid purple line) and post-irradiated with UV light for 10 minutes (dashed light purple line) to demonstrate photostability.

[0015] FIG. 7 shows three representative stress-strain curves for soft dogbones under cyclic loading, with a plot of hysteresis and elastic recovery for all 500 cycles shown as an inset relative to natural rubber as a control.

[0016] FIG. 8 shows plots of storage modulus and corresponding Tan 5 curves obtained using dynamic mechanical analysis at variable temperature.

[0017] FIG. 9 shows optical images of structures having soft-hard lines of varying width, spring equations for composites with hard and soft segments arranged in series and parallel, and images of samples containing 5 mm lines loaded in a tensile tester. Symbols: Er, composite modulus in series; E\\, composite modulus in parallel; ^365, hard volume fraction; ^9405, soft volume fraction; E365, hard tensile modulus; E405, soft tensile modulus.

[0018] FIG. 10 shows tensile moduli for samples tested in parallel and series, with dashed lines representing theoretical values from the spring model.

[0019] FIG. 11 shows nanoindentation across soft-hard interfaces within a single layer (left) and between layers where hard layers are either printed before (center) or after (right) printing soft layers. Indentations were performed every 50 micrometers (pm). Symbols represent an average of at least 10 measurements with error bars being ±1 standard deviation from the mean.

[0020] FIG. 12 shows nanoindentation data showing soft-hard interfacial gradient control on a bar achieved by overlaying greyscale (dose controlled) UV and violet light projections. Inset is a photograph of the shallow gradient.

[0021] FIG. 13 shows brick-and-mortar architecture akin to nacre in shells to control bulk toughness. Rendering and images of 3D printed structures (left) and stress-strain behavior relative to all-soft and all-hard controls. Solid lines represent pristine samples, dotted lines represent samples with an initial 2 mm defect.

[0022] FIG. 14 shows hard springs in a soft cylinder akin to spines in vertebrates to control compressive (damping) response. Rendering and images of representative 3D printed structures left) and force-displacement behavior relative to soft cylinder and hard spring controls. Inset image shows a hard spring with a 3 mm pitch compressed to 45% global strain.

[0023] FIG. 15 shows front and side-on renderings and representative images of 3D printed knee joint model with hard “bones” connected by soft “ligaments”, showing smooth and reversible motion in one direction.DETAILED DESCRIPTION

[0024] Objects with uniform compositions (i.e., monoliths) are nearly absent in biological structures. Instead, nature brings together multiple materials having disparate mechanical properties (e.g., hard and soft) in a specific spatial arrangement (i.e., architecture). This evolved combination of composition and structure leads to impressive mechanical behavior that cannot be achieved with a single material, including enhancements in toughness, fatigue resistance, and strength. This synergy, that leads to an unparalleled precision in both form and function for natural multi-materials, has sparked a flurry of research efforts to create scalable synthetic analogues using advanced manufacturing processes that offer high dimensional accuracy, resolution, and build speeds (e.g., 3D printing). However, to date, several contemporary hurdles have frustrated this realization, from slow production rates to unstable or mechanically weak products.

[0025] Previous two-step methods for multi-material 3D printing have faced various technical limitations such as monomer injection, required post-processing steps to provide desired properties, presence of unreacted monomer components, and time scales that are not relevant to printing. Here, the present inventors define eight desirable criteria for multi-material 3D printing that if collectively met would enable numerous fundamental studies and potential commercialization: 1) --build speeds >0.1 millimeter per minute (mm / min) (<60 s per 100 micrometer (pm) layer), 2) lack of small molecules in the final parts (e.g., no sol fraction), 3) difference in stiffness (z / Ej between hard and soft materials exceeding three orders of magnitude (>1000x), 4) high hard material strength (>50 megapascals (MPa)), 5) large soft material deformation (>100% strain) and 6) reversible soft material deformation (elastic recovery >95%), 7) good ambient, photo-, and thermal stability, and 8) spatially-programable mechanical properties (i.e., gradients) with high feature resolution (e.g., <500 pm). These eight criteria are based upon properties that can be achieved for single component (monolithic) structures using state-of-the-art 3D printing in addition to properties observed in natural multi-material objects. The predominant strategies that have emerged to meet the demand for high performance multi-material structures are topology optimization, multi-nozzle extrusion, multi-material jetting, multistep direct inkwriting, and multi- vat, -dose, or -color stereolithography (SLA). However, to date, no one strategy has addressed more than five out of the eight above criteria.

[0026] Provided herein is a method for multi-material 3D printing using a digital light processing (DLP) type 3D printer with dual wavelengths of light (e.g., ultraviolet (UV) light at 365 nm, and violet light at 405 nm), for example as shown in FIG. 1. For a facile manufacturing process, a single pot photocurable composition was developed which can provide a printed composition having different mechanical properties in a single step. In a specific example, an epoxide-acrylate hybrid monomer (e.g., 3,4-(epoxycyclohexyl)methyl acrylate (ECA)), enabled two types of reactivity as shown in FIG. 2. The acrylate moiety can undergo a free radical polymerization, and the epoxide moiety can undergo cationic ring-opening polymerization. Since the radical polymerization only requires one unpaired single electron (radical) generation where the cationic polymerization requires radical generation which is followed by acid generation for initiation of photo-polymerization, propagating acrylate groups is much faster and easier than opening the epoxide groups. From the perspective of printing speed, free radical polymerization is favorable, but it is difficult to achieve orthogonal printing with spectral control. Therefore, cationic ring-opening polymerization was adapted for an orthogonal multi -material printing using different wavelengths of light. To compensate for the printing time with epoxy resin, a highly strained cycloaliphatic epoxide (e.g., having a three- membered oxirane ring attached to a cyclohexene) was used. With a well-designed photosystem, a loosely crosslinked acrylate network for one light patterning and a tightly crosslinked acrylate-epoxide network for the other light patterning can be generated. A significant advantage is therefore provided by the present disclosure.

[0027] Accordingly, an aspect of the present disclosure is a photocurable composition. The photocurable composition comprises a hybrid monomer. As used herein, a “hybrid monomer” refers to a polymerizable compound having at least two functional groups which are polymerizable by different mechanisms. The at least two functional groups are covalently bound to the same molecule (i.e., the monomer). The term “hybrid monomer” is therefore distinct from a monomer composition which comprises more than one type of monomer wherein each type of monomer has a single polymerizable group. In an aspect, the hybrid monomer has two functional groups which are polymerizable by different mechanisms. In an aspect, the hybrid monomer has more than two total functional groups, at least two of which are polymerizable by different mechanisms. Specifically, the hybrid monomer can comprise a free radically polymerizable group and a cationically polymerizable group.

[0028] A “free radically polymerizable group” as used herein refers to a chemical moiety that is activated in the presence of a free radical initiator (i.e., an initiator capable of initiating freeradical polymerization) such that it is available for reaction with other compounds bearing free radically polymerizable groups. Suitable free radically polymerizable groups generally comprise ethylenic unsaturation. Exemplary free radically polymerizable groups can include, but are not limited to, acrylates, methacrylates, acrylamides, methacrylamides, alkenyl aromatics (e.g., styrene and derivatives thereof), vinyl groups (e.g., vinyl acetate), or a combination thereof. In an aspect, the hybrid monomer comprises a free radically polymerizable group that is a (meth)acrylate, preferably an acrylate.

[0029] In addition to the free radically polymerizable group, the hybrid monomer comprises a cationically polymerizable group. As used herein, a “cationically polymerizable group” refers to a chemical moiety that is activated in the presence of a cationic initiator (i.e., an initiator capable of initiating cationic polymerization) such that it is available for reaction with other compounds bearing cationically polymerizable groups. Cationic polymerization as used herein can include cationic ring opening polymerization. Exemplary cationically polymerizable groups can include, but are not limited to, a cyclic ether (e.g., an epoxy group, an oxetane group, or the like), a vinyl ether, an oxetane, a spiro-orthocarbonate, a spiro-orthoester, or a combination thereof. In a specific aspect, the cationically polymerizable group can comprise a cycloalkyl ether cationically polymerizable group, preferably an epoxy.

[0030] In a specific aspect, the hybrid monomer may comprise a methacrylate group or an acrylate group and an epoxy group or a vinyl ether group. For example, the hybrid monomer may be of the structurewherein L is a linking group and “CE” is a cyclic alkyl ether group, for example an epoxide (i.e., oxirane), an oxetane, or a moiety including an oxirane or oxetane ring, or a derivative thereof. The linking group can include, for example, a Ci-6 alkylene linking group. In a specific aspect, the linking group can be a methylene (i.e., -CH2-) linking group. In an aspect, CE can be an epoxycycloalkyl group, for example an epoxycyclohexyl group (e.g., a 3, 4-epoxy cyclohexyl group). In a very specific aspect, the hybrid monomer can comprise (3,4-epoxycyclohexyl)methyl acrylate or (3,4-epoxycyclohexyl)methyl methacrylate, for example having the structure

[0031] As will be understood by use of the term “monomer”, the hybrid monomer described herein refers to a compound that is a discrete chemical species with a defined composition and molecular weight. The hybrid monomer is a simple unpolymerized form of a chemical compound having relatively low molecular weight. Stated another way, the term “hybrid monomer” does not include oligomeric or polymeric species which include repeating units and can have a relatively high molecular weight and a molecular weight distribution. In an aspect, the hybrid monomer can have a molecular weight of 1,000 grams per mole (g / mol) or less, for example 750 g / mol or less, or 500 g / mol or less, or 300 g / mol or less, or 250 g / mol or less, or 50 to 750 g / mol, or 75 to 500 g / mol, or 100 to 750 g / mol, or 100 to 500 g / mol.

[0032] The hybrid monomer can be present in the photocurable composition in an amount of 1 to 99.98 weight percent, based on the total weight of the photocurable composition. Within this range, the hybrid monomer can be present in the photocurable composition in an amount of 10 to 99.98 weight percent, or 10 to 99.9 weight percent, or 10 to 95 weight percent, or 10 to 90 weight percent, or 20 to 99.98 weight percent, or 20 to 95 weight percent, or 20 to 90 weight percent, or 30 to 99.98 weight percent, or 30 to 95 weight percent, or 30 to 90 weight percent, or 50 to 99.98 weight percent, or 50 to 98 weight percent, or 50 to 95 weight percent, or 50 to 90 weight percent, or 65 to 99.98 weight percent, or 65 to 95 weight percent, or 65 to 90 weight percent, 70 to 99.98 weight percent, or 70 to 95 weight percent, or 70 to 90 weight percent, or 70 to 85 weight percent, each based on the total weight of the photocurable composition.

[0033] In addition to the hybrid monomer, the photocurable composition comprises a photoradical generator. As used herein, a “photoradical generator” refers to a polymerization initiator that can generate a radical when induced by light (e.g., infrared light, visible light, ultraviolet light, far-ultraviolet light, an X-ray, or a charged particle beam, such as an electron beam). Photoradical generators can therefore generate a radical in a chemical reaction caused by photoirradiation and initiate a radical polymerization. In an aspect, photoradical generators which generate a radical in response ultraviolet (UV), visible, or near infrared light can be preferred (i.e., in a range of 360 to 1000 nanometers). Photoradical generators which generate a radical in response to ultraviolet (UV) light, visible light, or both can be preferred.

[0034] Exemplary photoradical generators can include, but are not limited to, substituted or unsubstituted 2,4,5 -triarylimidazole dimers (e.g., 2-(o-chlorophenyl)-4,5-diphenylimidazole dimer, 2-(o-chlorophenyl)-4,5-di(methoxyphenyl)imidazole dimer, 2-(o-fluorophenyl)-4,5-diphenylimidazole dimer, 2-(o- or p-methoxyphenyl)-4,5-diphenylimidaole dimer, and the like); benzophenone and derivatives thereof (e.g., N,N'-tetramethyl-4,4'-diaminobenzophenone (Michler's ketone), N,N'-tetraethyl-4,4'-diaminobenzophenone, 4-methoxy-4- dimethylaminobenzophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, 4,4'- diaminobenzophenone, and the like); aromatic ketone derivatives (e.g., 2-benzyl-2- dimethylamino-l-(4-morpholinophenyl)-butanone-l,2-methyl-l-4-(methylthio)phenyl-2- morpholino-propanon-l-one); quinones (e.g., 2-ethylanthraquinone, phenanthrenequinone, 2-t- butylanthraquinone, octamethylanthraquinone, 1,2-benzanthraquinone, 2,3-benzanthraquinone, 2-phenylanthraquinone, 2,3-diphenylanthraquinone, 1 -chloroanthraquinone, 2- methylanthraquinone, 1,4-naphthoduinone, 9,10-phenanthrenequinone, 2-methyl-l,4- naphthoduinone, 2,3-dimethylanthraquinone, and the like); benzoin ether derivatives (e.g., benzoin methyl ether, benzoin ethyl ether, benzoin phenyl ether, and the like); benzoin and benzoin derivatives (e.g., methyl benzoin, ethylbenzoin, propylbenzoin, and the like); benzyl derivatives (e.g., benzyl dimethyl ketal); acridine derivatives (e.g., 9-phenylacridine and 1,7- bis(9,9’-acridinyl)heptane); N-phenylglycine and N-phenylglycine derivatives; acetophenone and acetophenone derivatives (e.g., 3-methyl acetophenone, acetophenone benzyl ketal, 1 - hydroxycyclohexyl phenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone); thioxanthone and thioxanthone derivatives (e.g., diethylthioxanthone, 2-isopropylthioxanthone, and 2- chloro thioxanthone); and phosphine oxides (e.g., phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and bis-(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide). Combinations comprising any of the foregoing photoradical generators can be used.

[0035] In an aspect, the photoradical generator can comprise a bis acylphosphine oxide. Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide can be preferred.

[0036] In an aspect, the photoradical generator can absorb light in the range of 300 to 1000 nanometers, or 300 to 700 nanometers, or 300 to 450 nanometers, or 310 to 440 nanometers, or 320 to 430 nanometers.

[0037] The photoradical generator can be present in the photocurable composition in an amount of, for example, 0.01 to 10 weight percent, based on the total weight of the photocurable composition. Within this range, the photoradical generator can be present in the photocurable composition in an amount of 0.01 to 5 weight percent, or 0.1 to 5 weight percent, or 0.1 to 3 weight percent, or 0.5 to 5 weight percent, or 0.5 to 3 weight percent, or 1 to 10 weight percent, or 1 to 5 weight percent, or 1 to 3 weight percent, each based on the total weight of the photocurable composition.

[0038] In addition to the hybrid monomer and the photoradical generator, the photocurable composition further comprises a photoacid generator. As used herein, a “photoacid generator”refers to a polymerization initiator that can generate a cationic species when induced by light (e.g., infrared light, visible light, ultraviolet light, far-ultraviolet light, an X-ray, or a charged particle beam, such as an electron beam). Photoacid generators can therefore generate a cationic species in a chemical reaction caused by photoirradiation and initiate cationic polymerization. In an aspect, photoacid generators which generate a cationic species in response to ultraviolet (UV), visible (Vis), or near infrared (NIR) light can be preferred (i.e., in a range of 360 to 1000 nanometers). Photoacid generators which generate an acidic group in response to ultraviolet (UV) light can be preferred. In an aspect, the photoacid generator may generate a Bronsted acid or a Lewis acid upon irradiation with light. In an aspect, the photoacid generator can be a triarylsulfonium salt, an aryldiazonium salt, a diaryliodonium salt, a dialkylphenacylsulfonium salt, or a sulfonic ester compound.

[0039] In a specific aspect, the photoacid generator comprises a triarylsulfonium salt. Exemplary triarylsulfonium salts can include bis[4-(diphenylsulfonio)phenyl]sulfide bis(hexafluoroantimonate), triphenylsulfonium hexafluoroantimonate, tris(4- methoxyphenyl)sulfonium hexafluorophosphate, diphenyl-4-thiophenoxyphenylsulfonium hexafluoroantimonate, diphenyl-4-thiophenoxyphenylsulfonium hexafluorophosphate, 4,4'- bis(diphenylsulfonio (phenyl sulfide-bis-hexafluoroantimonate, 4,4'-bis[di(P- hydroxyethoxy)phenylsulfonio]phenyl sulfide-bis-hexafluoroantimonate, 4,4'-bis | di( [)- hydroxy ethoxy )phenylsulfonio]phenyl sulfide-bis-hexafluorophosphate, 4- [4'-(benzoyl)phenylthio]phenyl-di-(4-fluorophenyl)sulfonium hexafluoroantimonate, and 4-[4'- (benzoyl)phenylthio]phenyl-di-(4-fluorophenyl)sulfonium hexafluorophosphate. Combinations of photoacid generators can also be used.

[0040] In an aspect, the photoacid generator can comprise bis[4- (diphenylsulfonio)phenyl]sulfide bis(hexafluoroantimonate).

[0041] Exemplary iodonium salts can include 4-octyloxydiphenyliodonium hexafluoroantimonate, isobutylphenyl-4’-methylphenyliodonium hexafluorophosphate, bis(4- tert-butylphenyl)iodonium hexafluorophosphate, and the like, or a combination thereof.

[0042] In an aspect the photoacid generator can absorb light in the range of 300 to 1000 nanometers, or 300 to 700 nanometers, or 300 to 500 nanometers, or 300 to 390 nanometers, or 310 to 380 nanometers, or 320 to 370 nanometers. In an aspect, the photoacid generator does not absorb light at a wavelength of greater than 390 nanometers, or greater than 380 nanometers.

[0043] The photoacid generator can be present in the photocurable composition in an amount of, for example, 0.01 to 20 weight percent, based on the total weight of the photocurable composition. Within this range, the photoacid generator can be present in the photocurable composition in an amount of 0.01 to 15 weight percent, or 0.01 to 10 weight percent, or 0. 1 to 20weight percent, or 0.1 to 15 weight percent, or 0.1 to 10 weight percent, or 1 to 20 weight percent, or 1 to 15 weight percent, or 1 to 10 weight percent, or 2 to 7 weight percent, each based on the total weight of the photocurable composition.

[0044] The photoradical generator and the photoacid generator in the photocurable composition can be selected based on their absorption profiles. For example, the photoradical generator and the photoacid generator should have non-overlapping or selectively overlapping absorption profiles. This is necessary to control the orthogonal chemistries of the hybrid monomer (i.e., the free radical polymerization and the cationic polymerization). Accordingly, in aspect, the photoradical generator can absorb light in at least one spectral region that does not substantially overlap with an absorption of the photoacid generator. In another aspect, the photoacid generator can absorb light in at least one spectral region that does not substantially overlap with an absorption of the photoradical generator. In yet another aspect, both the photoradical generator and the photoacid generator can absorb light in spectral regions that do not substantially overlap. The term “spectral region” as used herein refers a portion of the electromagnetic spectrum. As used herein in reference to the absorption profiles of the photoradical and photoacid generators, the term “substantially” means that the absorption of the photoradical generator and photoacid generator overlap by at most 50%, or 40%, or 30%, or 20%, or 10%, or 5%, or 4%, or 3%, or 2%, or 1%, or 0.5%, or 0.1%, or 0.01%, or 0.001% or less.

[0045] For example, in an aspect, the photoradical generator can absorb light in the range of 320 to 430 nanometers, and the photoacid generator can absorb light in the range of 320 to 370 nanometers. In an aspect, the photoacid generator does not absorb light at a wavelength of greater than 380 nanometers. So, the photoradical generator can absorb light in at least one spectral region that does not overlap with the absorption of the photoacid generator (i.e., at a wavelength of greater than 370 to 430 nanometers).

[0046] It is noted that other wavelength ranges and combinations are also contemplated by the present disclosure, provided that the conditions above are met. The selectively overlapping (or non-overlapping absorption) profiles of the photoradical generator and the photoacid generator are needed to achieve the desired orthogonal chemical reactions.

[0047] In addition to the hybrid monomer, the photoradical generator, and the photoacid generator, the photocurable composition can optionally further comprise a photosensitizer. The photosensitizer can preferably be a visible light or UV light sensitizer or near infrared light sensitizer. In an aspect, the photosensitizer can be a UV photosensitizer. The photosensitizer can be a molecule which is capable of absorbing light having wavelengths in the range of 300 to 1000 nanometers, for example 300 to 500 nanometers, or 300 to 450 nanometers, or 300 to 400 nanometers, or 300 to 390 nanometers. The photosensitizer can have an absorption maximum inthe range of 320 to 400 nanometers, or 320 to 390 nanometers. The photosensitizer is also preferably soluble in the photocurable composition.

[0048] Examples of suitable photosensitizers can include ketones, coumarin dyes (e.g., ketocoumarins), xanthene dyes, xanthone dye, thioxanthone dyes, acridine dyes, thiazole dyes, thiazine dyes, oxazine dyes, azine dyes, aminoketone dyes, porphyrins, aromatic polycyclic hydrocarbons, p-substituted aminostyryl ketone compounds, aminotriaryl methanes, merocyanines, squarylium dyes, pyridinium dyes, boron dipyrromethene (BODIPY), cyanine dyes, and phthalocyanine dyes. In an aspect, the photosensitizer can comprise a thioxanthone, for example according to the general formulawherein each occurrence of R1,R2, R3, R4, Rs, R6, R7, and R8are independently hydrogen, a Ci-6 alkyl group, or a Ci-6 alkoxy group. In a specific aspect, each of R1R2, R4, R5, R6, and R8are hydrogen, and R3and R7are each a Ci-6 alkoxy group, preferably a methoxy group (i.e., the photosensitizer can be 3,6-dimethoxy-9H-thioxanthen-9-one).

[0049] When present, the photosensitizer can be present in the photocurable composition in an amount of, for example, 0.01 to 10 weight percent, based on the total weight of the photocurable composition. Within this range, when present, the photosensitizer can be present in the photocurable composition in an amount of 0.1 to 10 weight percent, or 0.01 to 5 weight percent, or 0.1 to 5 weight percent, or 0.01 to 3 weight percent, or 0.1 to 3 weight percent, each based on the total weight of the photocurable composition.

[0050] The photocurable composition can optionally further comprise a reactive diluent. The reactive diluent comprises a free radically polymerizable group. In a specific aspect, the reactive diluent can comprise an acrylate group. The reactive diluent can optionally further comprise a functional group, preferably a functional group capable of interacting with at least one other component of the composition, wherein the interacting can comprise covalent interactions or noncovalent interactions (e.g., Van der Waals forces, hydrogen bonding, ionic interactions, and the like). In an aspect, a suitable reactive diluent can comprise a free radically polymerizable group and at least one hydroxyl group, or a free radically polymerizable group and an aliphatic Ci-20 alkyl group, or a free radically polymerizable group and a poly(alkylene oxide) group (e.g., a poly(ethylene oxide) group), or a free radically polymerizable group and a Ci-20 alkyl group comprising at least one carbamate linkage. In a specific aspect, the reactive diluent can comprisea free radically polymerizable group and a hydroxyl group (i.e., -OH). Thus, in an aspect, exemplary reactive diluents can be of the general formulawherein L is a linking group and X is a hydroxyl group or a methyl group. Linking groups can include, for example, a Ci-12 alkylene linking group, a Ci-12 alkylene oxide linking group, or a poly(Ci-6 alkylene oxide) linking group. In a specific aspect, L is a C1-12 alkylene linking group, preferably a C2 (i.e., ethylene) linking group and X is a hydroxyl group (i.e., the reactive diluent can comprise 2-hydroxyethyl acrylate).

[0051] When present, the reactive diluent can be included in the photocurable composition in an amount of 0.01 to 99 weight percent, based on the total weight of the photocurable composition. Within this range, when present, the reactive diluent can be included in the photocurable composition in an amount of 1 to 99 weight percent, or 5 to 99 weight percent, or 10 to 99 weight percent, or 10 to 95 weight percent, or 25 to 95 weight percent, or 50 to 99 weight percent, or 50 to 95 weight percent, or 10 to 80 weight percent, or 25 to 80 weight percent, or 5 to 80 weight percent, or 5 to 50 weight percent, or 5 to 45 weight percent, or 10 to 30 weight percent, each based on the total weight of the photocurable composition.

[0052] The photocurable composition can optionally further comprise a crosslinker. The crosslinker is not particularly restricted provided that it contains two or more reactive groups capable of reacting with the free radically polymerizable group of the hybrid monomer, the cationically polymerizable group of the hybrid monomer, or both. For example, a crosslinker can comprise two or more free radically polymerizable groups, two or more cationically polymerizable groups (e.g., epoxy groups), or a combination thereof. The crosslinker may also be considered to be a reactive diluent.

[0053] Preferably, the crosslinker comprises at least two free radically polymerizable groups. In an aspect, the crosslinker can comprise at least two acrylate groups. For example, suitable crosslinkers can include those according to the formulawherein L is a linking group, for example a C1-12 alkylene linking group, a C1-12 alkylene oxide linking group, or a poly(Ci-6 alkylene oxide) linking group.

[0054] When present, the crosslinker can be included in the photocurable composition in an amount of 0.01 to 80 weight percent, based on the total weight of the photocurable composition.Within this range, when present, the crosslinker can be included in the photocurable composition in an amount of 0.01 to 50 weight percent, or 0.01 to 25 weight percent, or 0.01 to 10 weight percent, or 0.01 to 5 weight percent, or 0.01 to 1 weight percent, or 0.01 to 0.5 weight percent, each based on the total weight of the photocurable composition.

[0055] It will be understood that the amount of each component of the composition is selected such that the total amount of the components sums to 100 weight percent.

[0056] In a specific aspect, the photocurable composition can comprise 1 to 99.8 weight percent of the hybrid monomer, 0.01 to 10 weight percent of the photoradical generator, and 0.01 to 20 weight percent of the photoacid generator, wherein weight percent of each component is based on the total weight of the photocurable composition. In another aspect, the photocurable composition can comprise 70 to 99.8 weight percent of the hybrid monomer, 0.01 to 10 weight percent, of the photoradical generator, and 0.01 to 20 weight percent of the photoacid generator, wherein weight percent of each component is based on the total weight of the photocurable composition. In another aspect, the photocurable composition can comprise 1 to 99.95 weight percent of the hybrid monomer, 0.01 to 10 weight percent of the photoradical generator, 0.01 to 20 weight percent of the photoacid generator, optionally 0.01 to 10 weight percent of the sensitizer, optionally 0.01 to 99 weight percent of the reactive diluent, and optionally 0.01 to 80 weight percent of the crosslinker, wherein weight percent of each component is based on the total weight of the photocurable composition.

[0057] In an aspect, the photocurable composition can comprise 50 to 90 weight percent of the hybrid monomer, 1 to 10 weight percent, of the photoradical generator, and 1 to 10 weight percent of the photoacid generator, wherein weight percent of each component is based on the total weight of the photocurable composition. In an aspect, the photocurable composition can comprise 80 to 98 weight percent of the hybrid monomer, 1 to 10 weight percent, of the photoradical generator, and 1 to 10 weight percent of the photoacid generator, wherein weight percent of each component is based on the total weight of the photocurable composition. In another aspect, the photocurable composition can comprise 50 to 90 weight percent of the hybrid monomer, 1 to 10 weight percent of the photoradical generator, 1 to 10 weight percent of the photoacid generator, optionally 0.1 to 5 weight percent of the sensitizer, optionally 5 to 45 weight percent of the reactive diluent, and optionally 0.01 to 5 weight percent of the crosslinker, wherein weight percent of each component is based on the total weight of the photocurable composition. In another aspect, the photocurable composition can comprise 80 to 98 weight percent of the hybrid monomer, 1 to 10 weight percent of the photoradical generator, 1 to 10 weight percent of the photoacid generator, optionally 0.1 to 5 weight percent of the sensitizer, optionally 5 to 45 weight percent of the reactive diluent, and optionally 0.01 to 5 weight percent of the crosslinker,wherein weight percent of each component is based on the total weight of the photocurable composition. In another aspect, the photocurable composition can comprise 75 to 92.89 weight percent of the hybrid monomer, 1 to 10 weight percent of the photoradical generator, 1 to 10 weight percent of the photoacid generator, 0.1 to 5 weight percent of the sensitizer, 5 to 45 weight percent of the reactive diluent, and 0.01 to 5 weight percent of the crosslinker, wherein weight percent of each component is based on the total weight of the photocurable composition. Other combinations based on ranges provided herein and combinations of various optional components are also contemplated by the present disclosure.

[0058] The photocurable composition can exclude or minimize components not explicitly described herein. In an aspect, the photocurable composition can minimize (e.g., less than 5 weight percent, or less than 1 weight percent, or less than 0.1 weight percent) or exclude a filler. In an aspect the photocurable composition can minimize (e.g., less than 5 weight percent, or less than 1 weight percent, or less than 0.1 weight percent) or exclude a solvent. In an aspect, the photocurable composition can minimize (e.g., less than 5 weight percent, or less than 1 weight percent, or less than 0. 1 weight percent) or exclude a polymerizable component other than the hybrid monomer and, when present, the reactive diluent or crosslinker.

[0059] The photocurable composition can optionally further comprise an additive composition, comprising one or more additives selected to achieve a desired property, with the proviso that the additive(s) are also selected so as to not significantly adversely affect a desired property of the photocurable composition (e.g., so as to not significantly adversely affect free radical generation and polymerization, cation generation and polymerization, or use in an additive manufacturing method. The additive composition or individual additives can be mixed with the photocurable composition at any suitable time during the mixing of the components for forming the composition. The additive(s) can be soluble or non-soluble in the photocurable composition. The additive composition can include, for example, a flow modifier, filler (e.g., glass, carbon, mineral, or metal), reinforcing agent (e.g., glass fibers), antioxidant, heat stabilizer, plasticizer, lubricant, release agent (such as a mold release agent), antistatic agent, anti-fog agent, antimicrobial agent, colorant (e.g., a dye or pigment), surface effect additive, radiation stabilizer, flame retardant, anti-drip agent (e.g., a PTFE-encapsulated styrene-acrylonitrile copolymer (TSAN)), opaquing agents, radical inhibitors, or a combination thereof. For example, a colorant, an opaquing agent, a radical inhibitor, a thickening agent, a filler, or a combination thereof can be used. The additives can be used in amounts generally known to be effective. For example, the total amount of the additive composition (other than any filler or reinforcing agent) can be 0.001 to 10.0 weight percent, or 0.01 to 5 weight percent, each based on the total weight of the photocurable composition.

[0060] The photocurable composition is preferably a homogenous liquid. That is, the photoradical generator, the photoacid generator, and, when present, the photosensitizer, and the crosslinker are soluble in the hybrid monomer and, when present, the reactive diluent or crosslinker. The reactive diluent and crosslinker, when present, are miscible with the hybrid monomer. In an aspect, the photocurable composition has a viscosity effective to facilitate three- dimensional printing with the composition. For example, in an aspect, the photocurable composition can have a viscosity of less than 1,000,000 centipoise (cP), for example less than 100,000 cP, or less than 50,000 cP, or less than 25,000 cP, or less than 10,000 cP, or less than 5,000 cP.

[0061] The photocurable composition described herein can be particularly useful for the manufacture of various cured compositions and articles. As described above, due to the careful selection of the photoradical generator, the photoacid generator, and the hybrid monomer, free radical polymerization and cationic polymerization can be carried out orthogonally. In an additional advantageous feature, the photocurable composition can provide cured products having various domains, wherein the chemical composition of each domain can be controlled by the polymerization mechanism employed in that area (i.e., by controlling the wavelength of light used to irradiate particular areas of the resin). Due to the variation in chemical composition in a single cured article, variations in mechanical properties can also be present. In an additional advantageous feature, the present inventors found that the domains can be well-defined, providing the variations in chemical composition in a pre-determined pattern having high resolution.

[0062] Accordingly, a cured product provided by polymerization of the photocurable composition represents another aspect of the present disclosure. The cured product is a multimaterial composition having varying compositions and properties depending on the chemical identity of the components. The cured product can comprise a first domain derived from polymerization of the free radically polymerizable group of the hybrid monomer and the cationically polymerizable group of the hybrid monomer; and a second domain derived from polymerization of the free radically polymerizable group of the hybrid monomer. The first domain is coupled (e.g., covalently bound) to the second domain at an interface between the first domain and the second domain. In an aspect, the first domain can have an elastic modulus that is greater than an elastic modulus of the second domain. Stated another way, the first domain can be a harder or stiffer material relative to the second domain. In an aspect the second domain has a strain at break that is greater than a strain at break for the first domain. In an aspect, the first domain can be a minor phase within the second domain. In an aspect, the cured product can comprise a plurality of first domains, and the first domains can be dispersed in the second domain.

[0063] The cured product can exhibit a desirable combination of properties. For example, the cured product can exhibit one or more of a stiffness disparity AE between the first domain and the second domain that is at least 1000 times, or at least 2000 times; a strength o-maxof at least 50 MPa, or at least 60 MPa, or at least 70 MPa; a strain at failure .-.r of greater than 100%, or greater than 125%; elastic recovery of at least 95%, or at least 99%; and hysteresis loss of less than 5% at 100% strain. In an aspect, the cured product can exhibit two of the foregoing properties, or three of the foregoing properties, or four of the foregoing properties. In an aspect, the cured product can exhibit each of the foregoing properties.

[0064] It will also be recognized that while the cured products described herein are capable of providing high resolution patterns (i.e., with distinct transitions between the first domain and the second domain), in some aspects, it can be desirable to provide a gradient transition between domains, for example to tune the resulting material properties.

[0065] A method for the manufacture of a cured multi-material composition represents another aspect of the present disclosure. The method comprises irradiating the photocurable composition of the present disclosure with light at a wavelength of light effective to polymerize the hybrid monomer. The wavelength of light can be selected to selectively activate the photoradical generator, the photoacid generator, or both to control whether polymerization occurs via the free radically polymerizable group, the cationically polymerizable group, or both. Accordingly, the method described herein used in conjunction with the photocurable composition of the present disclosure can provide a cured multi-material composition having varying compositions and properties (i.e., a “multi-material) depending on the chemical identity of the components and the wavelength selected for irradiation.

[0066] In an aspect, the method comprises irradiating the photocurable composition with a first wavelength of light, wherein the first wavelength of light is selected to activate the photoradical generator to initiate polymerization of the free radically polymerizable group of the hybrid monomer and to activate the photoacid generator to initiate polymerization of the cationically polymerizable group to provide a first domain. The method further comprises irradiating the photocurable composition with a second wavelength of light, wherein the second wavelength of light is selected to activate the photoradical generator to initiate polymerization of the free radically polymerizable group of the hybrid monomer to provide a second domain.

[0067] It is noted that the irradiation with the first wavelength or the second wavelength (i.e., to activate the photoradical generator or the photoacid generator) can be conducted in any order. For example, as an alternative, the method can comprise first irradiating the photocurable composition with a second wavelength of light, wherein the second wavelength of light is selected to activate the photoradical generator to initiate polymerization of the free radically polymerizablegroup of the hybrid monomer to provide a second domain, and subsequently irradiating the photocurable composition with a first wavelength of light, wherein the first wavelength of light is selected to activate the photoradical generator to initiate polymerization of the free radically polymerizable group of the hybrid monomer and to activate the photoacid generator to initiate polymerization of the cationically polymerizable group to provide a first domain.

[0068] Irradiation with the first and second wavelength of light can also be conducted simultaneously, but at different spatial locations in the photocurable composition. It will also be understood that the irradiating with the first or second wavelengths of light can be repeated as needed to provide a desired pattern of the first domain and the second domain in the cured composition.

[0069] In some aspects, the light intensity of one or both of the first and second wavelengths of light can be spatially varied. Spatially varying the wavelengths of light used to provide the cured multi-material composition can provide gradient compositions or transitions between the first and second domains. As such, the material properties of the cured compositions can be tuned based on the light intensity used across an area of the cured composition.

[0070] The first domain and the second domain are coupled (e.g., covalently bound) at an interface between the first domain and the second domain. The first domain and the second domain will differ, specifically with regard to crosslink density, based on the wavelength of light used. For example, when the first domain is provided by irradiating with a wavelength of light effective to activate both the photoradical generator to initiate polymerization of the free radically polymerizable group of the hybrid monomer and to activate the photoacid generator to initiate polymerization of the cationically polymerizable group, a highly crosslinked network will be provided. In contrast, when the second domain is provided by irradiating the photocurable composition with a second wavelength of light effective to activate the only photoradical generator to initiate polymerization of the free radically polymerizable group, the crosslink density will be less relative to the first domain. Thus, in an aspect, the first domain can have an elastic modulus that is greater than the elastic modulus of the second domain. The second domain can also have a strain at break that is greater than a strain at break for the first domain. Accordingly, the present inventors have advantageously discovered a photocurable composition that can provide a multimaterial having varying mechanical properties in a one-pot system.

[0071] In a further advantageous feature, no additional post-treatment steps are needed to obtain the desired multi-material composition or properties. For example, the method of the present disclosure can exclude a thermal post-treatment step or a photo-post-treatment step.

[0072] The first and second wavelengths of light can be selected based on the absorption profiles of the selected photoradical generator, photoacid generator, and when present, thephotosensitizer, as will be readily understood by the person having ordinary skill in the art guided by the present disclosure. For example, in an aspect, the photoradical generator can absorb light in the range of 320 to 430 nanometers, the photoacid generator can absorb light in the range of 320 to 370 nanometers, and the photoacid generator does not absorb light at a wavelength of greater than 380 nanometers. Accordingly, the first wavelength of light can be in the range of 320 to 375 nanometers, and the second wavelength of light can be in the range of 380 to 430 nanometers.

[0073] The method of the present disclosure can be an additive manufacturing method, also referred to in the art as three-dimensional (3D) printing. Suitable additive manufacturing methods can include those which are light based, including stereolithography, digital light processing, computed axial lithography (i.e., volumetric additive manufacturing), or a method using a liquid crystal display equipped with at least two light sources, wherein an emission profile of each light source does not overlap.

[0074] In an aspect, the 3D printing can be accomplished with the present photocurable composition in a digital light processing (DLP) method. In a 3D printer for a DLP method, the photocurable composition in liquid form can be provided in a vat or spread on a sheet. A predetermined area of the photocurable composition can be exposed to the selected wavelength of light (e.g., UV or visible light having a wavelength selected to activate the photoradical generator or the photoacid generator). The irradiation with light can be controlled by a digital micro-mirror device or a rotating mirror. In DLP, additional layers are repeatedly or continuously laid and each layer is cured until the desired 3D article is provided.

[0075] Because of the wavelength selectivity of the photoradical generator and the photoacid generator, 3D articles can be provided having varying compositions and mechanical properties, as described above. The aforementioned first and second domains can be provided in any pattern in the printed article.

[0076] This disclosure is further illustrated by the following examples, which are nonlimiting.EXAMPLES

[0077] For the following examples, a hybrid acrylate-epoxy monomer, (3,4- epoxycyclohexyl)methyl acrylate (ECA), was chosen for wavelength selective radical and cationic photocuring to create mechanically resolved multi-material thermosets (FIG. 2). Efficient Type I photoacid generation was optimized for epoxy curing with UV light exposure only, while a Type I radical photoinitiator was employed to induce acrylate curing upon exposure to either violet or UV light. This cross-reactivity was viewed as favorable given that the persistent acrylatenetwork would tie the two disparate domains together, strengthening the interfaces that are often points of failure in multi-material structures. Additionally, dual curing of hybrid acrylate-epoxy resins allowed for the incorporation of acrylate diluents to tune resin viscosity, photocuring rate, and material properties of the cured parts without leading to high sol fractions. Acrylate diluents incorporated into the present resin in the following examples were 2-hydroxyethyl acrylate (HEA) and tetra(ethylene glycol) diacrylate (TEGDA).

[0078] Photosystem optimization to achieve spectral control within the constraints of the present 3D printing system (<15 milliwatts per square centimeter (mW / cm2) and <80 mW / cm2from 365 nanometer (nm) and 405 nm LEDs, respectively) was accomplished using real-time Fourier transform infrared (RT-FTIR) spectroscopy to monitor monomer-to-polymer conversion ( / ?). Seven industrial photoacid generators (triarylsulfonium and diphenyliodonium salts) were screened with UV (365 nm) light exposure, while phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (B APO) was selected as the violet (405 nm) light reactive Type I radical photoinitiator (FIG. 3). Photoacid generator testing was accomplished using 3,4-epoxycyclohexylmethyl 3,4- epoxycyclohexanecarboxylate (ECC) as a proxy monomer owing to the overlap in epoxy and acrylate IR absorption bands when using ECA. Photoacid generators with ECC alone confirmed that the epoxide polymerization kinetics at ~10 mW / cm2365 nm LED exposure was insufficient for printing (e.g., >60 seconds to completion). However, among those tested, bis[4- (diphenylsulfonio)phenyl]sulfide bis(hexafluoroantimonate) (THS) led to one of the fastest epoxide conversion rates and was thus used going forward. Quantifying the spectral overlap (FIG. 3, shaded regions) between absorbance profiles of each compound and emission profiles of the 365 and 405 nm LEDs provided insight into their potential wavelength selective reactivity. The LED output profiles were collected after a 387 nm longpass dichroic beamsplitter (394 nm reflection cut-off and 375 nm transmission cut-on) to match the DLP setup, which reduces emission overlap to potentially improve spectral control. Average molar absorptivity values across each complete emission profile for the 365 and 405 nm LEDs, respectively, were approximately 930 and 570 M ’-cm1for BAPO and approximately 150 and 12 M ’-cm1for THS. Notably, the weak absorption of THS at 365 nm corresponded with the slow epoxide polymerizations observed.

[0079] To accelerate the cationic polymerizations, the use of photosensitizers exhibiting a stronger 365 nm absorption relative to THS was examined. Specifically, 4-isopropylthioxanthone was considered first given its common utility as an efficient photosensitizer. While this accelerated the cationic polymerization rate, it was not selective due to an appreciable absorption of both the 365 and 405 nm LEDs. Next, 3,6-dimethoxy-9H-thioxanthen-9-one (MeOTX) was used as a blue shifted photosensitizer to impart the desired selectivity, providing average molar absorptivity values of -1920 M^-cm1for the 365 nm LED, approximately 13 times higher than THS, and 17M ’-cm1for the 405 nm LED (FIG. 3). Furthermore, MeOTX increased the absorption contrast of UV vs. violet light relative to THS (contrast » 113 times for MeOTX vs. 12 times for THS).

[0080] Initial resin optimization was accomplished by monitoring acrylate and epoxy conversion during UV and violet irradiation using RT-FTIR (FIG. 4). An exemplary resin providing a good balance of polymerization speed, photosystem component solubility, viscosity, and mechanical properties contained ECA (67.9 mole percent (mol%)), BAPO (0.5 mol%), THS (1 mol%), MeOTX (0.5 mol%), HEA (30 mol%), and TEGDA (0. 1 mol%). Samples for RT-FTIR were placed between IR transparent plates (glass or salt) with a thickness of 50 pm to match printing conditions. The acrylate conversion was determined by tracking the disappearance of the sp2C-H stretch at 3100 cm’1. Upon exposure to either 365 or 405 nm LEDs (10 mW / cm2) acrylate rapidly polymerized (rate = 1.2 ± 0.1 M’s1), consistent with BAPOs non-selective absorption. Furthermore, a conversion of 50% (approximately half max) was reached after approximately 2 seconds of irradiation. This was further supported using photorheology, which provided a time to gelation of approximately 2 seconds using either 365 or 405 nm LEDs (10 mW / cm2), indicating that these conditions were suitable for DLP 3D printing.

[0081] Epoxy polymerization was similarly tracked using the C-O-C overtone stretch at 3915 cm’1and confirmed with the C-O-C stretch at 909 cm’1, which gave consistent results (FIG. 5). In the presence of acrylate functionality, these epoxy signals were convoluted, necessitating the use of a model acrylate-free resin to estimate the reactivity and selectivity of the present photosystem for epoxy polymerizations. Specifically, the proxy resin contained ECC (58.5 mol%), 3-ethyl-3-oxetanemethanol (OXA, 40 mol%), THS (1 mol%), and MeOTX (0.5 mol%). In analogy to HEA in the hybrid resin, OXA severed several roles, such as improving solubility of the photosystem components, lowering resin viscosity, and accelerating epoxy polymerization by providing additional hydroxyl initiation sites. Importantly, this photosystem was selective, initiating epoxy polymerizations upon exposure to the UV LED and not the violet one over the course of the experiment (approximately one minute), each at 10 mW / cm2(FIG. 5). The low maximum epoxy conversion upon exposure to UV light was attributed to early onset vitrification / gelation, which may vary for the hybrid resin given the presence of acrylate diluents. Impressively, the combined incorporation of OXA and MeOTX resulted in an approximately 170 times increase in epoxy polymerization rate upon exposure to UV light (365 nm, 10 mW / cm2). Specifically, the UV light-induced epoxy polymerization rate was 0.16 ± 0.16 M- s’1, reaching 50% of maximum conversion in approximately 4 seconds, indicating that these conditions were suitable for DLP 3D printing.

[0082] The hybrid resins comprising ECA (varied mol%), HEA (varied mol%), TEGDA (0.1 mol%), BAPO (0.5 mol%), THS (1 mol%), and MeOTX (0.5 mol%) were tested with amulticolor DLP 3D printing system equipped with 365 and 405 nm projectors (as shown in FIG. 1). Combining and aligning the two projections through a dichroic filter provided maximum intensities of approximately 15 mW / cm2(UV) and approximately 80 mW / cm2(violet) at the build plane (44 x 25 mm) with a pixel resolution of approximately 25 pm. Given fast acrylate conversion rates relative to epoxy under equivalent lighting conditions, the 365 nm LED was used at full intensity (15 mW / cm2), while the 405 nm LED was operated at partial power (5 or 15 mW / cm2as noted) for all prints. For a set layer thickness of 50 pm, lightly crosslinked acrylics could be 3D printed with 4 seconds of violet light exposure and heavily crosslinked acrylate-epoxy networks with 12 seconds of UV light exposure. These conditions fulfilled the first criterion, with a z-build speed of 0.25 mm / min (12 s / 50 pm layer). Although printing was possible using a 405 nm LED intensity of 5 mW / cm2, the smallest lateral features were approximately 100 pm (~ 4 pixels), while an intensity of 15 mW / cm2provided features <50 pm (approximately 1-2 pixels). Qualitatively, stiction forces were considerably higher when using the higher violet light intensity at equal exposure times. At light intensities of 15 mW / cm2, residual monomer and photosystem components could be efficiently removed by washing with acetone. This was particularly important for the violet light (405 nm) printed objects as it provided final parts that were true elastomers (criterion two), as opposed to organogels, which precluded toxicity concerns from leaching and had the added benefit of improved stability.

[0083] Upon 3D printing dogbone specimens from the hybrid resins for mechanical testing (gauge length = 20 mm, width = 4 mm, thickness = 0.5 mm) a difference in color between those prepared with UV versus violet light was apparent. UV light printed samples were yellow in color, while those prepared with violet light were colorless (FIG. 6, inset). This fortuitously provided visual contrast that facilitated further characterization of resolution. Quantifying the photochromism using UV-vis absorption spectroscopy revealed a 40% increase in total photon absorption after 12 seconds of UV irradiation. While the exact origin of this change in absorption was not determined, its lack of occurrence during violet light exposure suggested that it derived from the photoacid generation process. An added potential benefit of this photo-opacifying effect is improved vertical resolution by reducing exposure of regions past the active layer being cured.

[0084] The mechanical disparity for UV vs. violet light cured objects was subsequently assessed via uniaxial tensile testing of 3D printed dogbone specimens (FIG. 6). Optimization was accomplished by varying both the molar ratio of ECA:HEA and light exposure time per 50 pm layer. Altering the ECA:HEA ratio at a constant UV (365 nm) or violet (405 nm) light dosage per layer revealed that ratios >3:7 had comparable mechanical performance when printed with UV light, with a stark difference in elastic modulus (AE) of approximately 4000 times between samples printed with UV or violet light (criterion three). Increasing the content of HEA beyondthis ratio led to a precipitous drop in E for UV light printed samples, which was attributed to a decrease in crosslink density. Although similar for ECA:HEA ratios >3:7, the optimal difference in mechanical properties occurred at a 7:3 ratio, which was hypothesized to arise from improved dissolution of MeOTX in the resin, leading to increased epoxy conversion. At this 7:3 (ECA:HEA) ratio, samples printed with UV light showed a large increase in stiffness between 5 and 10 seconds of exposure, followed by a plateau. As a result, a UV light exposure time of 12 seconds / 50 pm layer was selected for all future prints. This provided stiff and strong plastics with an average elastic modulus (E) of 1700 ± 70 MPa, maximum strength (<rm) of 76 ± 16 MPa (criterion four), and a strain at break (Ef) of 7 + 1% (FIG. 6). The stiffness of green parts produced with this UV light exposure time proved comparable to samples that received additional UV exposure in a postcuring step (E = 2108 ± 43 MPa), suggesting that the present dosage provided strongly interconnected networks. In stark contrast, samples printed with violet light (then acetone washed and dried) were soft and elastic, irrespective of light intensity (5 or 15 mW / cm2) and exposure time (2-15 seconds, E ~ 0.5-1 MPa. Specifically, an exposure time of 4 seconds / 50 pm layer was selected going forward, where samples printed with 15 mW / cm2violet light provided an E = 0.54 + 0.05 MPa,= 0.6 ± 0.1 MPa, and f = 180 ± 30% (criterion five, FIG. 6, solid line). Furthermore, it was qualitatively noticed that soft samples effectively returned to their original shape post-deformation.

[0085] Elasticity of the soft sample (15 mW / cm2, acetone washed) was quantified using cyclic tensile testing. Specifically, samples were deformed to a strain of 100% and unloaded to zero stress repeatedly over 100 cycles, using a strain rate of 20% / minute (FIG. 7). To remove the Mullins effect (plastic deformation) commonly present in untreated elastomers, all samples were pre-strained over 3 loading and unloading cycles prior to further testing. Impressively, samples 3D printed with violet light showed an elastic recovery >99%, along with a hysteresis loss of ~3- 4% (criterion six). For context, natural rubber, known for its excellent elasticity, was characterized under identical conditions and provided a similar elastic recovery >99%, but it had a hysteresis loss that was >2 times larger (approximately 7-13%) relative to the soft hybrid epoxy-acrylate samples. The reduced hysteresis loss of the present soft network may result from low friction of the bulky cyclohexylepoxide sidechains.

[0086] The stability of violet light printed samples was assessed next, given the presence of unreacted epoxy functionality with the potential for deleterious mechanical instability to occur upon aging (criterion seven). Under standard aging conditions (i.e., not accelerated), acetone washed samples left on the benchtop under ambient conditions for 8 weeks showed no significant change in mechanical performance. Next, samples were tested under accelerated aging conditions with UV light exposure post 3D printing (dosage « 2.7 J / cm2). Samples rinsed only with isopropylalcohol to remove surface resin increased in stiffness by approximately 180 times (E = 362 ± 46 MPa). In contrast, samples washed with acetone showed no significant change in stiffness (E = 0.55 ± 0.06 MPa) post-UV exposure (FIG. 6). This was hypothesized to arise from the effective removal of photoacid generator by washing with acetone. Additionally, post-UV exposure of acetone-washed samples resulted in values for(= 0.89 ± 0.05 MPa) and gf (= 300 ± 60%) that were consistently superior to the corresponding green (and acetone washed) parts. This may arise from the removal of small molecules that can act as plasticizers or a very minor amount of additional crosslinking upon UV-exposure that results in a modest improvement in mechanical performance without altering stiffness. Overall, the lack of significant aging under both standard and UV-accelerated conditions underscores the significance of acetone washing as a simple postprocessing procedure.

[0087] The thermal stability of 3D printed parts produced from the hybrid resin was also characterized given the known susceptibility of strained cyclic ethers (e.g., epoxides) to react upon heating (FIG. 8). Dynamic mechanical analysis (DMA) under uniaxial tension (0.1% strain, 1 Hertz (Hz) frequency) for samples printed with violet light revealed a glass transition temperature (Tg) near ambient (0-50°C) followed by a rubbery storage modulus of 0.5 MPa, in accord with macroscopic tensile data. In contrast, the rubbery modulus of UV light printed samples, without post-treatment, was around 55 MPa (Eg« 120-140°C), which indicates a ~55x increase in crosslinking density relative to violet light prints. For soft (violet light cured) samples, the storage modulus remained relatively constant up to ~190°C, after which it began to increase due presumably to thermal activation and crosslinking of unreacted epoxy functionality. The epoxy activation was corroborated using differential scanning calorimetry (DSC) of liquid monomer, which revealed an exotherm at temperatures > 150°C, notably accelerated in the presence of THS. Furthermore, a thermal soak at 100°C for 10 minutes showed no significant change in storage modulus, emphasizing the thermal stability of soft parts. Overall, the hybrid epoxy-acrylate objects showed good thermal stability despite the presence of unreacted epoxy groups.

[0088] Resolution of multi-material prints was assessed both optically, using the difference in color between UV and violet light exposed regions, and mechanically using tensile testing and nanoindentation. Samples containing lines of alternating violet and UV exposure of equal area were 3D printed with spacings ranging from 5 mm to 0.1 mm (FIG. 9). Light microscopy visually showed sharp features down to 0.25 mm, with apparent blurring of edges occurring for 0.1 mm samples. Applying uniaxial tension to samples with lines parallel (||) or perpendicular (1) to the axis of strain was then used to determine macroscopic moduli and compare the values to an ideal composite spring model (FIG. 10). With a constant 1:1 hard-to-soft ratio, tensile modulus should be independent of feature size, providing theoretical values of 850(Ell) and 0.9 MPa (Ei) for lines in parallel and series, respectively. Experimentally, prints with lines >1 mm were in good agreement with the idealized spring model (FIG. 9 equation and FIG. 10 dashed lines). For example, the parallel and series moduli of 1 mm lines were 956 + 2 MPa and 1.6 + 0.3 MPa, respectively. However, as spacings decreased in size from 1 to 0.1 mm, the series moduli values progressively increased, deviating from the model until 0.1 mm where no apparent difference in modulus between parallel and series was observed. This was hypothesized to arise from slight overcure of the UV-light irradiated regions, which becomes more significant as the soft-hard interfacial area increases.

[0089] To test this conjecture, stiffness was mapped across soft-hard interfaces using nanoindentation. For comparison, samples were printed with both lateral (within a layer; x,y) and vertical (between layers; z) interfaces. In all cases, the contact moduli increased by ~3 orders of magnitude across the interface, in accord with the AE determined using tensile testing. Within a layer (x,y), this transition (or gradient) spanned approximately 200 pm across the soft-hard interface (FIG. 11, left), providing a slope of approximately 8,500 MPa / mm, comparable to recent reports of mechanical patterning in 2D. The transition region was postulated to arise from a combination of acid diffusion, light scattering, and / or exothermic reactions causing epoxy curing in regions adjacent to illuminated areas. A comparable approximately 200 pm gradient was observed for vertical interfaces where the hard (UV light cured) layers were printed first, followed by the soft (violet light cured) layers (FIG. 11, center). In contrast, printing hard layers onto soft ones resulted in a broader approximately 250 pm gradient and an approximately 100 pm overcure of the hard material into the soft layers. This overcure was attributed to transmission of UV light through the layer being actively printed, causing unintentional exposure to previous layers cured with violet light, which in turn induced epoxy crosslinking (FIG. 11, right).

[0090] To emulate structures found in nature requires the ability to program the interfacial gradient (criterion eight) from sharp (e.g., pm scale, as seen in knee entheses) to shallow (e.g., cm scale, as seen in squid beaks). To create shallower soft-hard gradients we developed a method to independently overlay greyscale UV and violet light projections (FIG. 12). In this manner, the dosage of UV and violet light was spatially controlled within each layer of a 3D printed bar (Ixwxh dimensions = 30x20x5 mm3). Tn the center of the bar over a distance of approximately 23 mm, the violet light intensity was varied from 2.5 to 0 mW / cm2(4 s / 50 pm layer), and the UV light intensity from 0 to 7.5 mW / cm2(12 s / 50 pm layer) in the same direction. The light intensity was set to half that of prior values to avoid high stiction forces from the large area projection within each layer. Furthermore, the large area projection was anticipated to accelerate curing due to the exotherm of polymerization and provide an extent of cure necessary for the desired mechanical gradient. Nanoindentation across the surface of this sample provided contact moduli that againspanned approximately 3 orders of magnitude (1 to 2000 MPa), however this time over approximately 20 mm. This provided a gradient of 100 MPa / mm, nearly 2 orders of magnitude shallower than the prior sharp gradient. Thus, multicolor greyscale DLP 3D printing represents a nascent method to program mechanical gradients between disparate domains within multimaterial objects.

[0091] Three proof-of-concept demonstrations were accomplished to highlight the utility of multi -material 3D printing in manufacturing bioinspired mechanical metamaterials (i.e., synthetic structures with unique bulk mechanical behavior) (FIG. 13-15). Specifically, brick- and - mortar architectures to tune tensile toughness (like nacre in shells), hard springs within soft cylinders to tune compressive damping (like spines in vertebrates), and hard “bones” connected by soft “ligaments” to provide smooth joints (like knees in humans). In the first example, a 3D printed structure comprising hard inclusions (“bricks”) from UV light exposure surrounded by a soft and stretchable matrix from violet light exposure resulted in a material with a tunable strain energy density (also referred to as “modulus of toughness”) (FIG. 13). Upon extension, defects in the matrix, such as cracks, were arrested upon encountering a “brick”. This resulted in stark strainhardening followed by the formation of several new cracks within the soft material, which dissipated energy prior to macroscopic failure. This resulted in a composite structure that behaved like the soft component in its ability to deform elastically, yet like the hard component in its resistance to rupture, providing a strain energy density approximately 7 times higher than the pure soft 3D printed analog. In a related effort to tune toughness, a macroscopic double network architecture was printed, where a rigid skeleton was embedded in a soft matrix (like rebar in concrete). In this example, the rigid skeleton contained thin regions that acted as sacrificial “bonds” to dissipate energy upon rupture without leading to macroscopic failure (FIG. 13, right). In both of these examples strain energy density could be tuned by the number, location, and geometry of hard inclusions within a given area of a soft matrix.

[0092] To showcase how compressive behavior could be tailored without altering overall geometry or creating voids, we designed a multi-material structure that contained a hard concentric twisted coil (“spring”) of varying pitch (FIG. 14) and diameter within a soft cylinder. Additionally, hard disks were placed at the top and bottom of the soft cylinder to qualitatively showcase interfacial strength given a lack of delamination at high stress and strain. As controls, a hard-only spring and soft-only cylinder (with hard top and bottom disks) were also prepared. Compressing samples of varying spring pitch from 4 to 3 to 2 mm at a rate of 0.01 mm / s (= 0.1% / s) resulted in distinct mechanical responses, with stiffness values increasing by ~4x. Moreover, at an ultimate force of 50 N the global compressive strains were 28%, 18%, and 8% for pitches of 4, 3, and 2 mm, respectively. In contrast, the soft cylinder control (no spring) reached 44% strain ata force of 50 N, while a hard spring alone having a 3 mm pitch compressed to 65% strain upon applying only ~l-2 N of force. Thus, the multi-material structures displayed a non-linear combination of properties, which showcases the rich landscape for materials design and testing that this platform offers. Reinforcing this point were an additional set of cylindrical structures having a hole in the center and a layered sandwich paneling architecture with alternating hard and soft disks, reminiscent of the forewing in beetles. Altering the width of the washer-shaped soft rings led to a distinct change in the apparent stiffness by > lOx without needing to change the outer dimensions of the cylinder. These examples highlight how multi-material fabrication can precisely tune bulk mechanical properties without altering surface geometry.

[0093] As a final demonstration, a detailed knee joint was 3D printed (FIG. 15). Using a scaled down model of a human knee, a rigid femur, patella, and tibia were produced using UV light, while soft and stretchable connective tissue (e.g., tendons and ligaments) were simultaneously printed using violet light. The entire structure was approximately 46.5 mm tall and approximately 17.5 mm wide at the knee, with the smallest portions (ligaments / tendons) being approximately 0.6 mm in diameter. Despite the small soft features and their proximity to larger hard domains during the print, each feature remained intact and free at every point between their intended top and bottom junctions. The excellent print fidelity enabled ease of unidirectional bending upon applying a weak force by hand, followed by an elastic retraction upon removing the force (FIG. 15). Therefore, multi-material 3D printing using the present hybrid resins enabled the production of lifelike joints with smooth motion.

[0094] Rapid and high-resolution wavelength-selective 3D printing of multi-material structures with biomimetic mechanical properties was demonstrated herein. The present paradigm leverages resins comprising hybrid epoxy-acrylate monomers together with a highly efficient photosystem to selectively induce cationic and radical polymerizations. This facilitated fast (0.25 mm / min) manufacturing of high fidelity (~200 pm) multi-material objects with an unprecedented combination of stiffness disparity between soft and hard domains ( E ~ 4000 times), strength ( Jmax ~ 76 MPa), stretchability (ey > 150%), elasticity (<5% hysteresis loss and >99% recovery), and stability under ambient (>8 weeks) and accelerated UV light and high temperature (>100°C) aging conditions. Furthermore, greyscale multicolor projection was demonstrated for the first time to controllably program mechanical gradients at soft-hard interfaces from 0.2 to 20 mm. This precision manufacturing of multi-material structures is anticipated to enable applications requiring conformal contact between hard and soft surfaces, such as soft robotics, sealants, and medical devices (e.g., prosthetics and wearable health monitors). Moreover, the process and materials will provide access to more accurate biological models for both educational and research purposes. A significant improvement is therefore provided by the present disclosure.

[0095] This disclosure further encompasses the following aspects.

[0096] Aspect 1: A photocurable composition comprising: a hybrid monomer comprising a free radically polymerizable group and a cationically polymerizable group; a photoradical generator; and a photoacid generator; wherein the photoradical generator absorbs light in at least one spectral region that does not substantially overlap with an absorption of the photoacid generator; or the photoacid generator absorbs light in at least one spectral region that does not substantially overlap with an absorption of the photoradical generator; or both the photoradical generator and the photoacid generator absorb light in spectral regions that do not substantially overlap.

[0097] Aspect 2: The photocurable composition of aspect 1, wherein the free radically polymerizable group comprises a (meth) acrylate group.

[0098] Aspect 3: The photocurable composition of aspect 1 or 2, wherein the cationically polymerizable group comprises an epoxy group, a vinyl ether, an oxetane, a spiro-orthocarbonate, or a spiro-orthoester, preferably wherein the cationically polymerizable group comprises an epoxy group.

[0099] Aspect 4: The photocurable composition of any of aspects 1 to 3, wherein the hybrid monomer comprises an acrylate group and an epoxy group.

[0100] Aspect 5: The photocurable composition of any of aspects 1 to 4, wherein the photoradical generator absorbs light in the range of 300 to 1000 nanometers, preferably 320 to 430 nanometers.

[0101] Aspect 6: The photocurable composition of any of aspects 1 to 5, wherein the photoradical generator comprises a bisacylaphosphine oxide, preferably phenylbis(2,4,6- trimethylbenzoyl)phosphine oxide.

[0102] Aspect 7: The photocurable composition of any of aspects 1 to 6, wherein the photoacid generator absorbs light in the range of in the range of 300 to 1000 nanometers, preferably in the range of 320 to 370 nanometers wherein the photoacid generator does not absorb light at a wavelength of greater than 380 nanometers.

[0103] Aspect 8: The photocurable composition of any of aspects 1 to 7, wherein the photoacid generator comprises a triarylsulfonium salt or an iodonium salt, preferably 4- octyloxydiphenyliodonium hexafluoroantimonate, isobutylphenyl-4'-methylphenyliodonium hexafluorophosphate, bis(4-tert-butylphenyl)iodonium hexafluorophosphate, bis(4- (diphenylsulfonio)phenyl)sulfide bis(hexafluoroantimonate), diphenyl(4-(phenylthio)phenyl)sulfonium hexafluoroantimonate, or 4-thiophenyl phenyl diphenyl sulfonium hexafluoroantimonate, preferably bis[4-(diphenylsulfonio)phenyl]sulfide bis (hexafluoroantimonate) .

[0104] Aspect 9: The photocurable composition of any of aspects 1 to 8, further comprising a photosensitizer.

[0105] Aspect 10: The photocurable composition of aspect 9, wherein the photosensitizer has an absorption maximum in the range of 300 to 1000 nanometers, preferably 320 to 400 nanometers.

[0106] Aspect 11: The photocurable composition of aspect 9 or 10, wherein the photosensitizer comprises a thioxanthone, preferably 3,6-dimethoxy-9H-thioxanthen-9-one.

[0107] Aspect 12: The photocurable composition of any of aspects 1 to 11, further comprises a reactive diluent comprising a free radically polymerizable group, preferably an acrylate group.

[0108] Aspect 13: The photocurable composition of aspect 12, wherein the reactive diluent further comprises a hydroxyl group.

[0109] Aspect 14: The photocurable composition of any of aspects 1 to 13, further comprising a crosslinker.

[0110] Aspect 15: The photocurable composition of any of claims 1 to 14, comprising: 1 to 99.98 weight percent of the hybrid monomer; 0.01 to 10 weight percent of the photoradical generator; 0.01 to 20 weight percent of the photoacid generator; and optionally, 0.01 to 10 weight percent of a photosensitizer; wherein weight percent of each component is based on the total weight of the photocurable composition.

[0111] Aspect 16: The photocurable composition of any of claims 1 to 15, comprising: 50 to 98 weight percent of the hybrid monomer; 1 to 10 weight percent of the photoradical generator; 1 to 10 weight percent of the photoacid generator; and optionally, 0.01 to 3 weight percent of a photosensitizer; wherein weight percent of each component is based on the total weight of the photocurable composition.

[0112] Aspect 17: The photocurable composition of claim 15 or 16, wherein the hybrid monomer comprise (3,4-epoxycyclohexyl)methyl acrylate or (3,4-epoxycyclohexyl)methyl methacrylate; the photoradical generator comprises a bisacylaphosphine oxide; the photoacid generator comprises a triarylsulfonium salt; and the photosensitizer comprises a thioxanthone.

[0113] Aspect 18: A cured product provided by polymerization of the photocurable composition of any of aspects 1 to 17.

[0114] Apsect 19: The cured product of aspect 18, wherein the cured product comprises: a first domain derived from polymerization of the free radically polymerizable group of the hybrid monomer and the cationically polymerizable group of the hybrid monomer; and a second domain derived from polymerization of the free radically polymerizable group of the hybrid monomer; wherein the first domain is coupled to the second domain at an interface between the first domainand the second domain; wherein the first domain has an elastic modulus that is greater than an elastic modulus of the second domain; and wherein the second domain has a strain at break that is greater than a strain at break for the first domain.

[0115] Aspect 20: The cured product of aspect 18 or 19, wherein the cured product exhibits one or more of: a stiffness disparity AE between the first domain and the second domain that is at least 1000 times, or at least 2000 times; a strength o-max of at least 50 MPa, or at least 60 MPa, or at least 70 MPa; a strain at failure ci- of greater than 100%, or greater than 125%; elastic recovery of at least 95%, or at least 99%; and hysteresis loss of less than 5% at 100% strain.

[0116] Aspect 21: A method for the manufacture of a multi-material composition, the method comprising: irradiating the photocurable composition of any of aspects 1 to 17 with a first wavelength of light, wherein the first wavelength of light is selected to activate the photoradical generator to initiate polymerization of the free radically polymerizable group of the hybrid monomer and to activate the photoacid generator to initiate polymerization of the cationically polymerizable group to provide a first domain; and irradiating the photocurable composition of any of aspects 1 to 17 with a second wavelength of light, wherein the second wavelength of light is selected to activate the photoradical generator to initiate polymerization of the free radically polymerizable group of the hybrid monomer to provide a second domain; wherein the first domain is coupled to the second domain at an interface between the first domain and the second domain; wherein the first domain has an elastic modulus that is greater than an elastic modulus of the second domain; and wherein the second domain has a strain at break that is greater than a strain at break for the first domain.

[0117] Aspect 22: The method of aspect 21, comprising irradiating the photocurable composition with the first wavelength of light and subsequently irradiating the photocurable composition with the second wavelength of light, or irradiating the photocurable composition with the second wavelength of light and subsequently irradiating the photocurable composition with the first wavelength of light.

[0118] Aspect 23: The method of aspect 21, comprising simultaneously irradiating the photocurable composition with the first wavelength of light and the second wavelength of light

[0119] Aspect 24: The method of any of aspects 21 to 23, wherein the first wavelength of light is 320 to 375 nanometers and the second wavelength of light is 380 to 430 nanometers.

[0120] Aspect 25: The method of any of aspects 21 to 24, wherein the method is an additive manufacture method, preferably a light-based additive manufacturing method, more preferably digital light processing, stereolithography, computed axial lithography, or a method using a liquid crystal display equipped with at least two light sources, wherein an emission profile of each light source does not overlap.

[0121] The compositions, methods, and articles can alternatively comprise, consist of, or consist essentially of, any appropriate materials, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any materials (or species), steps, or components, that are otherwise not necessary to the achievement of the function or objectives of the compositions, methods, and articles.

[0122] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. “Combinations” is inclusive of blends, mixtures, alloys, reaction products, and the like. The terms “first,” “second,” and the like, do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The terms “a” and “an” and “the” do not denote a limitation of quantity, and are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. “Or” means “and / or” unless clearly stated otherwise. Reference throughout the specification to “an aspect” means that a particular element described in connection with the aspect is included in at least one aspect described herein, and may or may not be present in other aspects. The term “combination thereof’ as used herein includes one or more of the listed elements, and is open, allowing the presence of one or more like elements not named. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various aspects.

[0123] Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears.

[0124] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which this application belongs. All cited patents, patent applications, and other references are incorporated herein by reference in their entirety. However, if a term in the present application contradicts or conflicts with a term in the incorporated reference, the term from the present application takes precedence over the conflicting term from the incorporated reference.

[0125] Compounds are described using standard nomenclature. For example, any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom. A dashthat is not between two letters or symbols is used to indicate a point of attachment for a substituent. For example, -CHO is attached through carbon of the carbonyl group.

[0126] Unless substituents are otherwise specifically indicated, each of the foregoing groups can be unsubstituted or substituted, provided that the substitution does not significantlyadversely affect synthesis, stability, or use of the compound. “Substituted” means that the compound, group, or atom is substituted with at least one (e.g., 1, 2, 3, or 4) substituents instead of hydrogen, where each substituent is independently nitro (-NO2), cyano (-CN), hydroxy (-OH), halogen, thiol (-SH), thiocyano (-SCN), C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, C1-6 haloalkyl, C1-9 alkoxy, C1-6 haloalkoxy, C3-12 cycloalkyl, C5-18 cycloalkenyl, C6-12 aryl, C7-13 arylalkylene (e.g., benzyl), C7-12 alkylarylene (e.g, toluyl), C4-12 heterocycloalkyl, C3-12 heteroaryl, C1-6 alkyl sulfonyl (-S(=O)2-alkyl), C6-12 arylsulfonyl (-S(=O)2-aryl), or tosyl (CH3C6H4SO2-), provided that the substituted atom’s normal valence is not exceeded, and that the substitution does not significantly adversely affect the manufacture, stability, or desired property of the compound. When a compound is substituted, the indicated number of carbon atoms is the total number of carbon atoms in the compound or group, including those of any substituents.

[0127] While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantia] equivalents.

Claims

CLAIMS1 . A photocurable composition comprising: a hybrid monomer comprising a free radically polymerizable group and a cationically polymerizable group; a photoradical generator; and a photoacid generator; wherein the photoradical generator absorbs light in at least one spectral region that does not substantially overlap with an absorption of the photoacid generator; or the photoacid generator absorbs light in at least one spectral region that does not substantially overlap with an absorption of the photoradical generator; or both the photoradical generator and the photoacid generator absorb light in spectral regions that do not substantially overlap.

2. The photocurable composition of claim 1 , wherein the free radically polymerizable group comprises a (meth)acrylate group.

3. The photocurable composition of claim 1, wherein the cationically polymerizable group comprises an epoxy group, a vinyl ether, an oxetane, a spiro-orthocarbonate, or a spiro- orthoester, preferably wherein the cationically polymerizable group comprises an epoxy group.

4. The photocurable composition of claim 1, wherein the hybrid monomer comprises an acrylate group and an epoxy group.

5. The photocurable composition of claim 1, wherein the photoradical generator absorbs light in the range of 300 to 1000 nanometers, preferably 320 to 430 nanometers.

6. The photocurable composition of claim 1, wherein the photoradical generator comprises a bisacylaphosphine oxide, preferably phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

7. The photocurable composition of claim 1, wherein the photoacid generator absorbs light in the range of 300 to 1000 nanometers, preferably in the range of 320 to 370 nanometers wherein the photoacid generator does not absorb light at a wavelength of greater than 380 nanometers.

8. The photocurable composition of claim 1, wherein the photoacid generator comprises a triarylsulfonium salt or an iodonium salt, preferably 4-octyloxydiphenyliodonium hexafluoroantimonate, isobutylphenyl-4'-methylphenyliodonium hexafluorophosphate, bis(4- tert-butylphenyl)iodonium hexafluorophosphate, bis(4-(diphenylsulfonio)phenyl)sulfide bis(hexafluoroantimonate), diphenyl(4-(phenylthio)phenyl)sulfonium hexafluoroantimonate, or 4-thiophenyl phenyl diphenyl sulfonium hexafluoroantimonate, preferably bis [4- (diphenylsulfonio)phenyl]sulfide bis(hexafluoroantimonate).

9. The photocurable composition of claim 1, further comprising a photosensitizer.

10. The photocurable composition of claim 9, wherein the photosensitizer has an absorption maximum in the range of 300 to 1000 nanometers, preferably 320 to 400 nanometers.

11. The photocurable composition of claim 9, wherein the photosensitizer comprises a thioxanthone, preferably 3,6-dimethoxy-9H-thioxanthen-9-one.

12. The photocurable composition of claim 1, further comprising a reactive diluent comprising a free radically polymerizable group, preferably an acrylate group.

13. The photocurable composition of claim 12, wherein the reactive diluent further comprises a hydroxyl group.

14. The photocurable composition of claim 1, further comprising a crosslinker.

15. The photocurable composition of claim 1, comprising:1 to 99.98 weight percent of the hybrid monomer;0.01 to 10 weight percent of the photoradical generator;0.01 to 20 weight percent of the photoacid generator; and optionally, 0.01 to 10 weight percent of a photosensitizer; wherein weight percent of each component is based on the total weight of the photocurable composition.

16. The photocurable composition of claim 1, comprising:50 to 98 weight percent of the hybrid monomer;1 to 10 weight percent of the photoradical generator;1 to 10 weight percent of the photoacid generator; and optionally, 0.01 to 3 weight percent of a photosensitizer;wherein weight percent of each component is based on the total weight of the photocurable composition.

17. The photocurable composition of claim 16, wherein the hybrid monomer comprise (3,4-epoxycyclohexyl)methyl acrylate or (3,4- epoxycyclohexyl)methyl methacrylate; the photoradical generator comprises a bisacylaphosphine oxide; the photoacid generator comprises a triarylsulfonium salt; and the photosensitizer comprises a thioxanthone.

18. A cured product provided by polymerization of the photocurable composition of claim 1.

19. The cured product of claim 18, wherein the cured product comprises: a first domain derived from polymerization of the free radically polymerizable group of the hybrid monomer and the cationically polymerizable group of the hybrid monomer; and a second domain derived from polymerization of the free radically polymerizable group of the hybrid monomer; wherein the first domain is coupled to the second domain at an interface between the first domain and the second domain; wherein the first domain has an elastic modulus that is greater than an elastic modulus of the second domain; and wherein the second domain has a strain at break that is greater than a strain at break for the first domain.

20. The cured product of claim 19, wherein the cured product exhibits one or more of: a stiffness disparity AE between the first domain and the second domain that is at least 1000 times, or at least 2000 times; a strength ainax of at least 50 MPa, or at least 60 MPa, or at least 70 MPa; a strain at failure cr of greater than 100%, or greater than 125%; elastic recovery of at least 95%, or at least 99%; and hysteresis loss of less than 5% at 100% strain.

21. A method for the manufacture of a multi-material composition from the photocurable composition of claim 1, the method comprising:irradiating the photocurable composition with a first wavelength of light, wherein the first wavelength of light is selected to activate the photoradical generator to initiate polymerization of the free radically polymerizable group of the hybrid monomer and to activate the photoacid generator to initiate polymerization of the cationically polymerizable group to provide a first domain; and irradiating the photocurable composition with a second wavelength of light, wherein the second wavelength of light is selected to activate the photoradical generator to initiate polymerization of the free radically polymerizable group of the hybrid monomer to provide a second domain; wherein the first domain is coupled to the second domain at an interface between the first domain and the second domain; wherein the first domain has an elastic modulus that is greater than an elastic modulus of the second domain; and wherein the second domain has a strain at break that is greater than a strain at break for the first domain.

22. The method of claim 21, comprising irradiating the photocurable composition with the first wavelength of light and subsequently irradiating the photocurable composition with the second wavelength of light, or irradiating the photocurable composition with the second wavelength of light and subsequently irradiating the photocurable composition with the first wavelength of light.

23. The method of claim 21, comprising simultaneously irradiating the photocurable composition with the first wavelength of light and the second wavelength of light.

24. The method of claim 21, further comprising spatially varying an intensity of the first wavelength of light, spatially varying an intensity of the second wavelength of light, or both to provide a gradient transition between the first domain and the second domain.

25. The method of claim 21, wherein the first wavelength of light is 320 to 375 nanometers and the second wavelength of light is 380 to 430 nanometers.

26. The method of claim 21, wherein the method is an additive manufacture method, preferably a light-based additive manufacturing method, more preferably digital light processing, stereolithography, computed axial lithography, or a method using a liquid crystaldisplay equipped with at least two light sources, wherein an emission profile of each light source does not overlap.

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