WO2020131675A1

WO2020131675A1 - Energy absorbing dual cure polyurethane elastomers for additive manufacturing

Info

Publication number: WO2020131675A1
Application number: PCT/US2019/066479
Authority: WO
Inventors: Matthew S. MENYO; R. Nicholas CARMEAN; Leah Marie HEIST; Yongqiang Li; Nickolaus MACKAY; Clarissa GUTIERREZ
Original assignee: Carbon, Inc.
Priority date: 2018-12-21
Filing date: 2019-12-16
Publication date: 2020-06-25

Abstract

Provided herein according to some embodiments is a polymerizable liquid useful for the production of an energy absorbing three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof by additive manufacturing. The polymerizable liquid may include components having soft segments (e.g., polyol/polyamine midblocks, chain extenders) of different number average molecular weights.

Description

ENERGY ABSORBING DUAL CURE POLYURETHANE ELASTOMERS

FOR ADDITIVE MANUFACTURING

BACKGROUND

Some additive manufacturing techniques, particularly bottom-up and top-down stereolithography, make a three-dimensional object by light polymerization of a resin (see, e.g., US Patent No. 5,236,637 to Hull). Unfortunately, such techniques have been generally considered slow, and have typically been limited to resins that produce brittle or fragile objects suitable only as prototypes.

A more recent technique known as continuous liquid interface production (CLIP) allows both more rapid production of objects by stereolithography (see, e.g., J. Tumbleston et al., Continuous liquid interface production of 3D Objects, Science 347, 1349-1352 (2015) and

US Patent Nos. 9,205,601; 9,211,678; 9,216,546; 9,360,757; and 9,498,920 to DeSimone et al.), and the production of parts with isotropic mechanical properties (see R. Janusziewcz et al., Layerless fabrication with continuous liquid interface production, Proc. Natl. Acad. Sci. USA 113, 11703-11708 (2016)).

Still further, the recent introduction of dual cure additive manufacturing resins by Rolland et al. (see, e.g., US Patent Nos. 9,676,963; 9,598,606; and 9,453,142), has additionally made possible the production of a much greater variety of functional and useful objects suitable for real world use.

Together, these developments have created an increased demand for additive manufacturing resins and systems that allow for the production of objects with diverse or finely-tuned mechanical properties.

SUMMARY

Provided herein according to some embodiments is a polymerizable liquid useful for the production of an energy absorbing three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof by additive manufacturing, said polymerizable liquid comprising: (a) a mixture of blocked or reactive blocked prepolymers (e.g., 40-90% by weight of the liquid) (b) a polyol and/or polyamine chain extender (e.g., 5-20% by weight of the liquid) (c) optionally a blocked or reactive blocked diisocyanate, or a blocked or reactive blocked diisocyanate chain extender, (d) optionally a reactive diluent (e.g., 15-35% by weight of the liquid); and (e) a photoinitiator (e.g., 0.5-2% by weight of the liquid), wherein, the mixture of prepolymers comprise prepolymers having soft segments (e.g., polyol/polyamine 5 midblocks) of different number average molecular weights.

In some embodiments, the mixture of prepolymers comprises: (i) prepolymers with soft segments (e.g., a (meth)acrylate blocked polyurethane, or ^MABPU") having a lower number average molecular weight of 200-900 Da, such as 250-700 Da; and (ii) prepolymers with soft segments (e.g., an ABPU) having a higher number average molecular weight of 1000-10,000 Da, such as 1500-5000 Da.

In some embodiments, the prepolymers with soft segments having the lower number average molecular weight is present in the liquid in an amount of from 1 to 20% by weight, such as 2-10% by weight

In some embodiments, the prepolymers with soft segments having the higher number average molecular weight is present in the liquid in an amount of from 15 to 45% by weight, such as 20-40% by weight.

In some embodiments, the higher number average molecular weight ABPU midblock is 2,000 Da poly(tetramethylene oxide) and lower number average molecular weight ABPU midblock is 650 Da poly(tetramethylene oxide).

In some embodiments, the soft segments of the prepolymers comprise polyethers, for example, poly(tetramethylene oxide), polypropylene glycol), polyethylene glycol), poly(trimethylene oxide) and copolymers thereof.

In some embodiments, the isocyanate for one of the blocked prepolymers in the mixture is different from the other, such as in which one is IPDI and one is HMDI.

In some embodiments, the chain extender comprises a rigid chain extender such as MACM (e.g., present at 1-10% by weight).

In some embodiments, the mixture of blocked or reactive blocked prepolymers is a mixture of ABPUs.

Also provided is a polymerizable liquid useful for the production of an energy absorbing three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof by additive manufacturing, said polymerizable liquid comprising a mixture of: (a) a blocked or reactive blocked prepolymer (e.g., ABPU) having a soft segment formed from a polyol/polyamine (i.e., midblock); (b) at least one polyol and/or polyamine chain extender; (c) optionally, a blocked or reactive blocked diisocyanate, or a blocked or reactive blocked diisocyanate chain extender; (d) optionally, a reactive diluent; and (e) a photoinitiator, wherein, one of the midblock and chain extender has a higher soft segment number average molecular weight of from 1000-10,000 Da, more preferably 1500-5000 Da, and the other has a lower soft segment number average molecular weight of from 200-900 Da, more preferably 250-700 Da.

In some embodiments, the chain extender is a polyether di- or triamine, and/or the soft segment of the prepolymer is formed with a polyether di- or triamine.

In some embodiments, the chain extender has the lower number average molecular weight and is present in an amount of 1-30 percent by weight, and the midblock is present in an amount from 15-45 percent by weight

In some embodiments, the midblock of the prepolymer has the lower number average molecular weight and is present in an amount of 5-40 percent by weight and the chain extender is present in an amount of 5-35 percent by weight

In some embodiments, the polyamine chain extender is Jeffamine D230, or T403. In some embodiments, the polyamine chain extender is Jeffamine D2000, T3000 or T5000.

In some embodiments, the lower number average molecular weight soft segment is 650 Da poly(tetramethylene oxide).

In some embodiments, the polymerizable liquid comprises a mixture of 2, 3, 4 or 5 different reactive diluents. In some embodiments, the polymerizable liquid comprises a mixture of 2 or 3 different chain extenders.

In some embodiments, the three-dimensional object has a glass transition temperature in a range of from 0 to 40 degrees Celsius.

Further provided is a polymerizable liquid useful for the production of an energy absorbing three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof by additive manufacturing, said polymerizable liquid comprising a mixture of: (a) at least one constituent selected from the group consisting of (i) a blocked or reactive blocked diisocyanate prepolymer, (ii) a blocked or reactive blocked diisocyanate, and (i) a blocked or reactive blocked diisocyanate chain extender; (b) at least one polyol and/or polyamine chain extender, which is present in an amount that is off-stoichiometry from the reactive functionality of the blocked functional groups (e.g., isocyanates) of (a); (c) optionally a reactive diluent; and (d) a photoinitiator. In some embodiments, the molar ratio of blocked isocyanates to polyol/polyamine is 0.75-1.25, preferably 0.8-0.95 or 1.05-1.2. In some embodiments, the polymerizable liquid comprises a mixture of 2, 3, 4 or 5 different reactive diluents. In some embodiments, the polymerizable liquid comprises a mixture of 2 or 3 different chain extenders.

Also provided is a method of forming an energy absorbing three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof, comprising: (a) providing a polymerizable liquid as taught herein, said liquid comprising: (i) a light polymerizable first component, and (ii) a second solidifiable component that is different from said first component; (b) producing a three-dimensional intermediate from said polymerizable liquid by an additive manufacturing process including irradiating said polymerizable liquid with light to form a solid polymer scaffold from said first component and containing said second solidifiable component carried in said scaffold in unsolidified and/or uncured form, said intermediate having the same shape as, or a shape to be imparted to, said three-dimensional object; (c) optionally cleaning said intermediate (e.g., by washing, wiping (with a blade, absorbent, compressed gas, etc.), gravity draining, centrifugal separation of residual resin therefrom, etc., including combinations thereof); and (d) concurrently with or subsequent to said producing step (b), heating, microwave irradiating, or both, said second solidifiable component in said three-dimensional intermediate, to form said energy absorbing three- dimensional object comprising polyurethane, polyurea, or a copolymer thereof.

In some embodiments, the producing step (b) is carried out by stereolithography (e.g., bottom-up stereolithography such as continuous liquid interface production).

In some embodiments, the producing step (b) is carried out by: (i) providing a carrier and an optically transparent member having a build surface, said carrier and said build surface defining a build region therebetween; (ii) filling said build region with said polymerizable liquid; and (Hi) irradiating said build region with light through said optically transparent member to form said solid polymer scaffold from said first component and also advancing said carrier and said build surface away from one another to form said three- dimensional intermediate.

In some embodiments, step (d) is carried out subsequent to said producing step (b), and optionally but preferably subsequent to said cleaning step (c).

In some embodiments, the three-dimensional object produced is elastomeric.

In some embodiments, the three-dimensional object produced has a Tan Delta (tanD) maximum occurring at a temperature of from 0°C to 40°C, and wherein the tanD maximum is greater than 0.3, when measured on a sample nominally 1 mm thick, 10 mm wide, and 10-15 mm long using a Dynamic Mechanical Analyzer with a Tension Clamp at a strain of 0.1% and at a frequency of lHz and a temperature ramp rate of 3°C/min.

In some embodiments, the three-dimensional object comprises a part of automotive damping and insulation, helmet energy absorption layer, bicycle seat, or a cushioning.

Still further provided is a three-dimensional object produced by a method as taught herein. In some embodiments, the object comprises a UV -polymerized component and a polyurethane/poiyurea component, which are optionally interpenetrating networks, semi- interpenetrating networks, or polymeric blends.

In some embodiments, the UV-polymerized component and the soft segment of the polyurethane/poiyurea component are phase-mixed or partially phase-mixed. In some embodiments, the polyurethane/poiyurea component comprises soft segments and hard segments that are phase-mixed or partially phase-mixed. In some embodiments, the polyurethane/poiyurea component comprises soft segments of low number average molecular weight and high number average molecular weight.

In some embodiments, the polyurethane/poiyurea component comprises hard segments of dissimilar backbone structure (e.g, EPDI and HMDI, IPDI and MACM).

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1-9 present graphs of TanD versus temperature for three-dimensional objects made in accordance with Examples 1-9 herein, as discussed further below.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention is now described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art

As used herein, the term "and/or" includes any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative ("or").

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly-used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and claims and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein. Well- known functions or constructions may not be described in detail for brevity and/or clarity.

"Shape to be imparted to" refers to the case where the shape of the intermediate object slightly changes between formation thereof and forming the subsequent three-dimensional product, typically by shrinkage (e.g., up to 1, 2 or 4 percent by volume), expansion (e.g., up to 1, 2 or 4 percent by volume), removal of support structures, or by intervening forming steps (e.g., intentional bending, stretching, drilling, grinding, cutting, polishing, or other intentional forming after formation of the intermediate product, but before formation of the subsequent three-dimensional product). The three-dimensional intermediate may also be washed, if desired, before further curing, and/or before, during, or after any intervening forming steps.

1. POLYMERIZABLE LIQUIDS (RESINS1.

Polymerizable liquid compositions curable by actinic radiation (typically light, and in some embodiments ultraviolet (UV) light) are provided to enable the present invention. The liquid (sometimes referred to as "liquid resin," "ink," or simply "resin" herein) may include a polymerizable monomer, particularly photopolymerizable and/or free radical polymerizable monomers (e.g., reactive diluents) and/or prepolymers (i.e., reacted or larger monomers capable of further polymerization), and a suitable initiator such as a free radical initiator.

Polyurethane dual cure resins for forming a three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof are described in, for example, Rolland et al., US Patent Nos. 9,676,963, 9,598,606, and 9,453,142, the disclosures of which are incorporated herein by reference. In general, such resins can comprise: (a) light- polymerizable monomers and/or prepolymers that can form an intermediate object (typically in the presence of a photoinitiator); and (b) heat-polymerizable (or otherwise further polymerizable) monomers and/or prepolymers.

Photoinitiators useful in the present invention include, but are not limited to, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), phenylbis(2,4,6- trimethylbenzoyl)phosphine oxide (PPO), 2-isopropylthioxanthone and/or 4- isopropylthioxanthone (ITX), etc. Light-polymerizable monomers and/or prepolymers. Sometimes also referred to as "Part A" of the resin, these are monomers and/or prepolymers that can be polymerized by exposure to actinic radiation or light. This resin can have a functionality of two or higher (though a resin with a functionality of one can also be used when the polymer does not dissolve in its monomer). A purpose of Part A is to "lock" the shape of the object being formed or create a scaffold for the one or more additional components (e.g., Part B). Importantly, Part A is present at or above the minimum quantity needed to maintain the shape of the object being formed after the initial solidification during photolithography. In some embodiments, this amount corresponds to less than ten, twenty, or thirty percent by weight of tiie total resin (polymerizable liquid) composition.

Examples of suitable reactive end groups suitable for Part A constituents, monomers, or prepolymers include, but are not limited to: acrylates, methacrylates, a-olefins, N-vinyls, acrylamides, methacrylamides, styrenics, epoxides, thiols, 1,3-dienes, vinyl halides, acrylonitriles, vinyl esters, maleimides, and vinyl ethers.

An aspect of the solidification of Part A is that it provides a scaffold in which a second reactive resin component, termed "Part B," can solidify during a second step, as discussed further below.

Heat-polymerizable monomers and/or prepolymers. Sometimes also referred to as "Part B," these constituents may comprise, consist of or consist essentially of a mix of monomers and/or prepolymers that possess reactive end groups that participate in a second solidification reaction during or after the Part A solidification reaction. In general, for dual cure resins, examples of methods used to solidify Part B include, but are not limited to, contacting the object or scaffold to heat, water or water vapor, light at a different wavelength than that at which Part A is cured, catalysts, (with or without additional heat), evaporation of a solvent from the polymerizable liquid (e.g., using heat, vacuum, or a combination thereof), microwave irradiation, etc., including combinations thereof. In some embodiments, heat curing of the "Part B" resins is preferred.

In some embodiments, the second component of the dual cure resin comprises precursors to a polyurethane, polyurea, or copolymer thereof (e.g., po ly (urethane-urea)) , and may also comprise a silicone resin, an epoxy resin, a cyanate ester resin, or a natural robber.

Resins may be in any suitable form, including "one pot" resins and "dual precursor" resins (where cross-reactive constituents are packaged separately, and which may be identified, for example, as an "A" precursor resin and a "B" precursor resin). Note that, in some embodiments employing "dual cure" polymerizable resins, the part, following manufacturing, may be contacted with a penetrant liquid, with the penetrant liquid carrying a further constituent of the dual cure system, such as a reactive monomer, into the part for participation in a subsequent cure. Such "partial" resins are intended to be included herein. See, e.g., WO 2018/094131 (Carbon, Inc.), the disclosures of which are incorporated herein by reference.

Examples of dual cure photopolymerizable reactive prepolymers include isocyanate or blocked isocynate-containing prepolymers. A blocked isocyanate is a group that can be deblocked or is otherwise available for reaction as an isocyanate upon heating, such as by a urethane reaction of an isocyanate with alcohol. See, e.g., U.S. Patent No. 3,442,974 to Bremmer; U.S. Patent No. 3,454,621 to Engel; Lee et al., "Thermal Decomposition Behaviour of Blocked Diisocyanates Derived from Mixture of Blocking Agents," Macromolecular Research, 13(5):427-434 (2005).

"Isocyanate" as used herein includes diisocyanate, polyisocyanate, and branched isocyanate.

"Diisocyanate" and "polyisocyanate" are used interchangeably herein and refer to aliphatic, cycloaliphatic, and aromatic isocyanates that have at least two, or in some embodiments more than two, isocyanate (NCO) groups per molecule, on average. In some embodiments, the isocyanates have, on average, 2.1, 2.3, 2.5, 2.8, or 3 isocyanate groups per molecule, up to 6, 8 or 10 or more isocyanate groups per molecule, on average. In some embodiments, the isocyanates may be a hyperbranched or dendrimeric isocyanate (e.g, containing more than 10 isocyanate groups per molecule, on average, up to 100 or 200 more more isocyanate groups per molecule, on average). Common examples of suitable isocyanates include, but are not limited to, methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI)), para-phenyl diisocyanate (PPDI), 4,4'-dicyclohexylmethane- diisocyanate (HMD I), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), triphenylmethane-4,4^,4"-triisocyanate, tolune-2,4,6- triyl triisocyanate, 1, 3, 5-triazine-2, 4,6- triisocyanate, ethyl ester L-lysine triisocyanate, etc., including combinations thereof. Numerous additional examples are known and are described in, for example, US Patent Nos. 9,200,108, 8,378,053, 7,144,955, 4,075,151, 3,932,342, and in US Patent Application

Publication Nos. US 20040067318 and US 20140371406, the disclosures of all of which are incorporated by reference herein in their entirety.

"Branched isocyanate" as used herein refers to diisocyanates or polyisocyanates as described above that have three or more isocyanate groups per molecule, or (with respect to mixtures of different isocyanates) more than two isocyanate groups per molecule, on average. In some embodiments, the branched isocyanates have, on average, 2.1, 2.3, 2.5, 2.8, or 3 isocyanate groups per molecule, up to 6, 8 or 10 or more isocyanate groups per molecule, on average. In some embodiments, the isocyanates may be hyperbranched or dendrimeric isocyanates as discussed above (e.g, containing more than 10 isocyanate groups per molecule, on average, up to 100 or 200 or more isocyanate groups per molecule, on average).

The blocking group may optionally have a reactive terminal group (e.g., a polymerizable end group such as an epoxy, alkene, alkyne, or thiol end group, for example an ethylenically unsaturated end group such as a vinyl ether).

In some embodiments, the dual cure resin includes a UV-curable (meth)acrylate blocked polyurethane/polyurea (ABPU). Such resins are described in, for example, Rolland et al., US Patent Nos. 9,676,963, 9,598,606, and 9,453,142, the disclosures of which are incorporated herein by reference.

An ABPU "midblock" is that section of the prepolymer or ABPU where a polyol or polyamine was reacted with isocyanate and a reactive blocking group (such as TBAEMA) to make an ABPU, including but not limited to poIy(tetramethylene oxide), polypropylene glycol), polyethylene glycol), poly(trimethylene oxide) and copolymers thereof. See US Patent No. 9,598,606 to Rolland et al.

In some embodiments, the isocyanate may be blocked with an amine methacrylate blocking agent (e.g., tertiary-butylaminoethyl methacrylate (TBAEMA), tertiary pentylaminoethyl methacrylate (TPAEMA), tertiary hexylaminoethyl methacrylate (THAEMA), tertiary-butylaminopropyl methacrylate (TBAPMA), maleimide, and mixtures thereof (see, e.g., US Patent Application Publication No. 20130202392)). Note that these could be used as diluents, as well.

Chain extenders. Chain extenders are generally linear compounds having di- or polyfunctional ends that can react with a monomer/prepolymer or crosslinked photopolymerized polymer intermediate as taught herein. Examples include, but are not limited to, diol or amine chain extenders, which can react with isocyanates of a de-blocked diisocyanate-containing polymer.

Examples of diol or polyol chain extenders include, but are not limited to, ethylene glycol, diethylene glycol, triethylene glycol, tetraethyiene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, hydroquinone bis(2- hydroxyethyl) ether (HQEE), glycerol, trimethylolpropane, 1,2,6-hexanetriol, and pentaerythritol. Natural oil polyols (biopolyols) may also be used. Such polyols may be derived, e.g., from vegetable oils (triglycerides), such as soybean oil, by known techniques. See, e.g., U.S. Patent No. 6,433,121 to Petrovic et al.

Examples of diamine or polyamine chain extenders include, but are not limited to, aliphatic, aromatic, and mixed aliphatic and aromatic, polyamines, such as diamines (for example, 4,4'-methylenedicyclohexanamine (PACM), 4,4'-methylenebis(2-methylcyclohexyl- amine) (MACM), ethylene diamine, isophorone diamine, diethyltoluenediamine), and polyetheramines (for example JEFF AMINE® from Huntsman Corporation).

Diluents. Diluents as known in the art are compounds used to reduce viscosity in a resin composition. Reactive diluents undergo reaction to become part of the polymeric network. In some embodiments, the reactive diluent may react at approximately the same rate as other reactive monomers and/or prepolymers in the composition. Reactive diluents may include aliphatic reactive diluents, aromatic reactive diluents, and cycloaliphatic reactive diluents. Examples include, but are not limited to, isobomyl acrylate, isobomyl methacrylate, lauryl acrylate, lauryl methacrylate, 2-ethyl hexyl methacrylate, 2-ethyl hexyl acrylate, di(ethylene glycol) methyl ether methacrylate, phenoxyethyl methacrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, dimethyl(aminoethyl) methacrylate, butyl acrylate, butyl methacrylate, cyclohexyl methacrylate, tetrahydrofurfuryl methacrylate, ethylene glycol dimethacrylate, hexanediol dimethacrylate, and tert-butylaminoethyl methacrylate.

Oxidizable tin salts. Oxidizable tin salts useful for carrying out the present invention include, but are not limited to, stannous butanoate, stannous octoate, stannous hexanoate, stannous heptanoate, stannous linoleate, stannous phenyl butanoate, stannous phenyl stearate, stannous phenyl oleate, stannous nonanoate, stannous decanoate, stannous undecanoate, stannous dodecanoate, stannous stearate, stannous oleate, stannous undecenoate, stannous 2- ethylhexoate, dibutyl tin dilaurate, dibutyl tin dioleate, dibutyi tin distearate, dipropyl tin dilaurate, dipropyl tin dioleate, dipropyl tin distearate, dibutyl tin dihexanoate, and combinations thereof. See also US Patent Nos. 5,298,532, 4,421,822, and 4,389,514, the disclosures of which are incorporated herein by reference. In addition to the foregoing oxidizable tin salts, Lewis acids such as those described in Chu et ai. in Macromolecular Symposia, Volume 95, Issue 1, pages 233-242, June 1995 are known to enhance the polymerization rates of free-radical polymerizations and are included herein by reference.

Fillers. Any suitable filler may be used in connection with the present invention, depending on the properties desired in the part or object to be made. Thus, fillers may be solid or liquid, organic or inorganic, and may include reactive and non-reactive rubbers: siloxanes, acrylonitrile-butadiene rubbers; reactive and non-reactive thermoplastics (including but not limited to: poly(ether imides), maleimide-styrene terpolymers, polyaryl ates, polysulfones and polyethersulfones, etc.) inorganic fillers such as silicates (such as talc, clays, silica, mica), glass, carbon nanotubes, graphene, cellulose nanocrystals, etc., including combinations of all of the foregoing. Suitable fillers include tougheners, such as core-shell rubbers, as discussed below.

Tougkeners. One or more polymeric and/or inorganic tougheners can be used as a filler in the present invention. The toughener may be uniformly distributed in the form of particles in the cured product The particles could be less than 5 microns (pm) in diameter. Such tougheners include, but are not limited to, those formed from elastomers, branched polymers, hyperbranched polymers, dendrimers, rubbery polymers, rubbery copolymers, block copolymers, core-shell particles, oxides or inorganic materials such as clay, polyhedral oligomeric siisesquioxanes (POSS), carbonaceous materials (e.g., carbon black, carbon nanotubes, carbon nanofibers, fullerenes), ceramics and silicon carbides, with or without surface modification or functionalization. Examples of block copolymers include the copolymers whose composition is described in U.S. Pat No. 6,894,113 (Court et al., Atofina, 2005) and include "NANOSTRENTH®" SBM (polystyrene-polybutadiene- polymethacrylate), and AMA (polymethacrylate-polybutylacrylate-polymethacrylate), both produced by Arkema (King of Prussia, Pennsylvania). Other suitable block copolymers include FORTEGRA® and the amphiphilic block copolymers described in U.S. Pat No. 7,820,760B2, assigned to Dow Chemical. Examples of known core-shell particles include the core-shell (dendrimer) particles whose compositions are described in US20100280151A1 (Nguyen et al., Toray Industries, Inc., 2010) for an amine branched polymer as a shell grafted to a core polymer polymerized from polymerizable monomers containing unsaturated carbon- carbon bonds, core-shell rubber particles whose compositions are described in EP 1632533A1 and EP 2123711 Al by Kaneka Corporation, and the "KaneAce MX" product line of such particle/epoxy blends whose particles have a polymeric core polymerized from polymerizable monomers such as butadiene, styrene, other unsaturated carbon-carbon bond monomer, or their combinations, and a polymeric shell compatible with the epoxy, typically polymethylmethacrylate, polyglycidylmethacrylate, polyacrylonitrile or similar polymers, as discussed further below. Also suitable as block copolymers in the present invention are the "JSR SX" series of carboxylated polystyrene/polydivinylbenzenes produced by JSR Corporation; "Kureha Paraloid" EXL-2655 (produced by Kureha Chemical Industry Co., Ltd.), which is a butadiene alkyl methacrylate styrene copolymer, "Stafiloid" AC-3355 and TR-2122 (both produced by Takeda Chemical Industries, Ltd.), each of which are acrylate methacrylate copolymers; and "PARALOIDⁿ EXL-2611 and EXL-3387 (both produced by Rohm & Haas), each of which are butyl acrylate methyl methacrylate copolymers. Examples of suitable oxide particles include NANOPOX® produced by nanoresins AG. This is a master blend of functionalized nanosilica particles and an epoxy.

CoreskeU rubbers . Core-shell rubbers are particulate materials (particles) having a rubbery core. Such materials are known and described in, for example, US Patent Application Publication No. 20150184039, as well as US Patent Application Publication No. 20150240113, and US Patent Nos. 6,861,475, 7,625,977, 7,642,316, 8,088,245, and elsewhere.

In some embodiments, the core-shell rubber particles are nanoparticles (i.e., having an average particle size of less than 1000 nanometers (nm)). Generally, the average particle size of the core-shell rubber nanoparticles is less than 500 nm, e.g., less than 300 nm, less than 200 nm, less than 100 nm, or even less than 50 nm. Typically, such particles are spherical, so the particle size is the diameter, however, if the particles are not spherical, the particle size is defined as the longest dimension of the particle.

In some embodiments, the rubbery core can have a glass transition temperature (Tg) of less than -25 °C, more preferably less than -50 °C, and even more preferably less than -70 °C. The Tg of the rubbery core may be well below -100 °C. The core-shell rubber also has at least one shell portion that preferably has a Tg of at least 50 °C. By "core," it is meant an internal portion of the core-shell rubber. The core may form the center of the core-shell particle, or an internal shell or domain of the core-shell rubber. A shell is a portion of the core-shell rubber that is exterior to the rubbery core. The shell portion (or portions) typically forms the outermost portion of the core-shell rubber particle. The shell material can be grafted onto the core or is cross-linked. The rubbery core may constitute from 50 to 95%, or from 60 to 90%, of the weight of the core-shell rubber particle.

The core of the core-shell rubber may be a polymer or copolymer of a conjugated diene such as butadiene, or a lower alkyl acrylate such as n-butyl-, ethyl-, isobutyl- or 2- ethylhexylacrylate. The core polymer may in addition contain up to 20% by weight of other copolymerized mono-unsaturated monomers such as styrene, vinyl acetate, vinyl chloride, methyl methacrylate, and the like. The core polymer is optionally cross-linked. The core polymer optionally contains up to 5% of a copolymerized graft-linking monomer having two or more sites of unsaturation of unequal reactivity, such as diallyl maleate, monoallyl fumarate, allyl methacrylate, and the like, at least one of the reactive sites being non- conjugated.

The core polymer may also be a silicone rubber. These materials often have glass transition temperatures below -100 °C. Core-shell rubbers having a silicone rubber core include those commercially available from Wacker Chemie, Munich, Germany, under the trade name GENIOPERL®.

The shell polymer, which is optionally chemically grafted or cross-linked to the rubber core, can be polymerized from at least one lower alkyl methacrylate such as methyl methacrylate, ethyl methacrylate or t-butyl methacrylate. Homopolymers of such methacrylate monomers can be used. Further, up to 40% by weight of the shell polymer can be formed from other monovinylidene monomers such as styrene, vinyl acetate, vinyl chloride, methyl acrylate, ethyl acrylate, butyl acrylate, and the like. The molecular weight of the grafted shell polymer can be between 20,000 and 500,000.

One suitable type of core-shell rubber has reactive groups in the shell polymer which can react with an epoxy resin or an epoxy resin hardener. Glycidyl groups are suitable. These can be provided by monomers such as glycidyl methacrylate.

One example of a suitable core-shell rubber is of the type described in US Patent Application Publication No. 2007/0027233 (EP 1 632 533 Al). Core-shell rubber particles as described therein include a cross-linked rubber core, in most cases being a cross-linked copolymer of butadiene, and a shell which is preferably a copolymer of styrene, methyl methacrylate, glycidyl methacrylate and optionally acrylonitrile. The core-shell rubber is preferably dispersed in a polymer or an epoxy resin, also as described in the document.

Suitable core-shell rubbers include, but are not limited to, those sold by Kaneka Corporation under the designation Kaneka Kane Ace, including the Kaneka Kane Ace 15 and 120 series of products, including Kaneka Kane Ace MX 120, Kaneka Kane Ace MX 153,

Kaneka Kane Ace MX 154, Kaneka Kane Ace MX 156, Kaneka Kane Ace MX170, Kaneka Kane Ace MX 257 and Kaneka Kane Ace MX 120 core-shell rubber dispersions, and mixtures thereof.

Additional resin ingredients. The liquid resin or polymerizable material can have solid particles suspended or dispersed therein. Any suitable solid particle can be used, depending upon the end product being fabricated. The particles can be metallic, organic/polymeric, inorganic, or composites or mixtures thereof. The particles can be nonconductive, semi-conductive, or conductive (including metallic and non-metallic or polymer conductors); and the particles can be magnetic, ferromagnetic, paramagnetic, or nonmagnetic. The particles can be of any suitable shape, including spherical, elliptical, cylindrical, etc. The particles can be of any suitable size (for example, ranging from 1 nm to 20 pm average diameter).

The .particles can comprise an active agent or detectable compound as described below, though these may also be provided dissolved solubilized in the liquid resin as also discussed below. For example, magnetic or paramagnetic particles or nanoparticles can be employed.

The liquid resin can have additional ingredients solubilized therein, including pigments, dyes, active compounds or pharmaceutical compounds, detectable compounds (e.g., fluorescent, phosphorescent, radioactive), etc., again depending upon the particular purpose of the product being fabricated. Examples of such additional ingredients include, but are not limited to, proteins, peptides, nucleic acids (DNA, RNA) such as siRNA, sugars, small organic compounds (drugs and drug-like compounds), etc., including combinations thereof.

Non-reactive tight absorbers . In some embodiments, polymerizable liquids for carrying out the present invention include a non-reactive pigment or dye that absorbs light, particularly UV light. Suitable examples of such light absorbers include, but are not limited to: (i) titanium dioxide (e.g., included in an amount of from 0.05 or 0.1 to 1 or 5 percent by weight), (ii) carbon black (e.g., included in an amount of from 0.05 or 0.1 to 1 or 5 percent by weight), and/or (iii) an organic ultraviolet light absorber such as a hydroxybenzophenone, hydroxyphenylbenzotri azole, oxanilide, benzophenone, thioxanthone, hydroxyphenyltriazine, and/or benzotriazole ultraviolet light absorber (e.g., Mayzo BLS1326) (e.g., included in an amount of 0.001 or 0.005 to 1, 2 or 4 percent by weight). Examples of suitable organic ultraviolet light absorbers include, but are not limited to, those described in US Patent Nos. 3,213,058; 6,916,867; 7,157,586; and 7,695,643, the disclosures of which are incorporated herein by reference.

Inhibitors of polymerization. Inhibitors or polymerization inhibitors for use in the present invention may be in the form of a liquid or a gas. hi some embodiments, gas inhibitors are preferred. In some embodiments, liquid inhibitors such as oils or lubricants (e.g., fluorinated oils such as perfluoropolyethers) may be employed, as inhibitors (or as release layers that maintain a liquid interface). The specific inhibitor will depend upon tire monomer being polymerized and the polymerization reaction. For free radical polymerization monomers, the inhibitor can conveniently be oxygen, which can be provided in the form of a gas such as air, a gas enriched in oxygen (optionally but in some embodiments preferably containing additional inert gases to reduce combustibility thereof), or in some embodiments pure oxygen gas. In alternate embodiments, such as where the monomer is polymerized by a photoacid generator initiator, the inhibitor can be a base such as ammonia, trace amines (e.g., methyl amine, ethyl amine, di and trialkyl amines such as dimethyl amine, diethyl amine, trimethyl amine, triethyl amine, etc.), or carbon dioxide, including mixtures or combinations thereof.

Polyurethane segments. In some embodiments, resin compositions of the present invention useful to form an energy absorbing three-dimensional object include components having soft segments of different number average molecular weights. For example, the resin may include components (e.g. , prepolymers and/or chain extenders) having a lower average molecular weight soft segment of 200-900 Da, such as 250-700 Da; and components having a higher average molecular weight of 1000-10,000 Da, such as 1500-5000 Da.

"Soft segment" and "hard segment" as used herein have their usual meaning in the polymer chemistry field and refer to sections of a polymer or prepolymer.

"Soft segment" refers to a typically oligomeric (or repeating low molecular weight) segment of the polyurethane chain that has a glass transition temperature less than room temperature, is generally amorphous or partially crystalline, provides flexibility to the copolymer, and generally has a large number of degrees of freedom. Examples of soft segments include, but are not limited to, polyethers, such as poly(tetramethylene oxide), polypropylene glycol), poly(ethylene glycol), poly(trimethylene oxide) and copolymers thereof.

"Hard segment" as used herein refers to a higher glass transition temperature, generally crystalline, rigid, segment that can provide mechanical integrity or strength to the segmented copolymer. Examples of hard segments include, but are not limited to, those formed from the reaction of isocyanates (such as IPDI, HMDI, HDI) and isocyanate-reactive amines and polyols (such as MACM).

In some preferred embodiments, there is phase mixing of different formulation components in the final article with different glass transition temperatures, such that the glass transition temperature (Tg) of the combined article is in the desired temperature of interest, preferably 0-40°C.

Stoichiometry of Part B components. In some embodiments, resin compositions of the present invention useful to form an energy absorbing three-dimensional object include Part B components present in molar deficiency or excess to the molar amount of blocked reactive groups. For example, the resin composition may include polyol and/or polyamine chain extenders that are present in an amount such that the moles of reactive groups (e.g, active hydrogen of amines or alcohols) are unequal to the moles of blocked functional groups (e.g., diisocyanates). As an example, the molar ratio of blocked isocyanates to polyol/polyamine in the resin may be 0.75-1.25, preferably 0.8-0.95 or 1.05-1.2.

2. ADDITIVE MANUFACTURING METHODS AND APPARATUS.

The polymerizable resins may be used for additive manufacturing, typically bottom- up or top-down additive manufacturing, generally known as stereolithography. Such methods are known and described in, for example, US Patent No. 5,236,637 to Hull, US Patent Nos. 5,391,072 and 5,529,473 to Lawton, US Patent No. 7,438,846 to John, US Patent No. 7,892,474 to Shkolnik, US Patent No. 8,110,135 to El-Siblani, US Patent Application Publication No. 2013/0292862 to Joyce, US Patent Application Publication No. 2013/0295212 to Chen et al., and US Patent Application Publication No. 2018/0290374 to Willis et al. The disclosures of these patents and applications are incorporated by reference herein in their entireties.

In general, top-down three-dimensional fabrication with a dual cure resin is carried out by:

(a) providing a polymerizable liquid reservoir having a polymerizable liquid fill level and a carrier positioned in the reservoir, the carrier and the fill level defining a build region therebetween;

(b) filling tiie build region with a polymerizable liquid (i.e., the resin), said polymerizable liquid comprising a mixture of (i) a light (typically ultraviolet light) polymerizable liquid first component, and (ii) a second solidifiable component of the dual cure system; and then

(c) irradiating the build region with light to form a solid polymer scaffold from the first component and also advancing (typically lowering) the carrier away from the build surface to form a three-dimensional intermediate having the same shape as, or a shape to be imparted to, the three-dimensional object and containing said second solidifiable component (e.g., a second reactive component) carried in the scaffold in unsolidified and/or uncured form.

A wiper blade, doctor blade, or optically transparent (rigid or flexible) window, may optionally be provided at the fill level to facilitate leveling of the polymerizable liquid, in accordance with known techniques. In the case of an optically transparent window, the window provides a build surface against which the three-dimensional intermediate is formed, analogous to the build surface in bottom-up three-dimensional fabrication as discussed below.

In general, bottom-up three-dimensional fabrication with a dual cure resin is earned out by:

(a) providing a carrier and an optically transparent member having a build surface, the carrier and the build surface defining a build region therebetween;

(b) filling the build region with a polymerizable liquid (/.*., the resin), said polymerizable liquid comprising a mixture of (i) a light (typically ultraviolet light) polymerizable liquid first component, and (ii) a second solidifiable component of the dual cure system; and then

(c) irradiating the build region with light through said optically transparent member to form a solid polymer scaffold from the first component and also advancing (typically raising) the carrier away from tike build surface to form a three-dimensional intermediate having the same shape as, or a shape to be imparted to, the three-dimensional object and containing said second solidifiable component (e.g., a second reactive component) carried in the scaffold in unso!idified and/or uncured form.

In some embodiments of bottom-up or top-down three-dimensional fabrication as implemented in the context of the present invention, the build surface is stationary during the formation of the three-dimensional intermediate; in other embodiments of bottom-up three- dimensional fabrication as implemented in the context of the present invention, the build surface is tilted, slid, flexed and/or peeled, and/or otherwise translocated or released from the growing three-dimensional intermediate, usually repeatedly, during formation of the three- dimensional intermediate.

In some embodiments of bottom-up or top-down three-dimensional fabrication as carried out in the context of the present invention, the polymerizable liquid (or resin) is maintained in liquid contact with both the growing three-dimensional intermediate and the build surface during both the filling and irradiating steps, during fabrication of some of, a major portion of, or all of the three-dimensional intermediate.

In some embodiments of bottom-up or top-down three-dimensional fabrication as carried out in the context of the present invention, the growing three-dimensional intermediate is fabricated in a layerless manner (e.g., through multiple exposures or "slices" of patterned actinic radiation or light) during at least a portion of the formation of the three- dimensional intermediate. In some embodiments of bottom-up or top-down three-dimensional fabrication as carried out in the context of the present invention, the growing three-dimensional intermediate is fabricated in a layer-by-layer manner (e.g., through multiple exposures or "slices" of patterned actinic radiation or light), during at least a portion of the formation of the three- dimensional intermediate.

In some embodiments of bottom-up or top-down three-dimensional fabrication employing a rigid or flexible optically transparent window, a lubricant or immiscible liquid may be provided between the window and the polymerizable liquid (e.g., a fluorinated fluid or oil such as a perfluoropolyether oil).

From the foregoing it will be appreciated that, in some embodiments of bottom-up or top-down three-dimensional fabrication as carried out in the context of the present invention, the growing three-dimensional intermediate is fabricated in a layerless manner during the formation of at least one portion thereof, and that same growing three-dimensional intermediate is fabricated in a layer-by-layer manner during the formation of at least one other portion thereof. Thus, operating mode may be changed once, or on multiple occasions, between layerless fabrication and layer-by-layer fabrication, as desired by operating conditions such as part geometry.

In some embodiments, the intermediate is formed by continuous liquid interface production (CLIP). CLIP is known and described in, for example, US Patent Nos. 9,205,601; 9,211,678; 9,216,546; 9,360,757; and 9,498,920 to DeSimone et al. In some embodiments,

CLIP employs features of a bottom-up three-dimensional fabrication as described above, but the irradiating and/or advancing steps are carried out while also concurrently maintaining a stable or persistent liquid interface between the growing object and the build surface or window, such as by: (i) continuously maintaining a dead zone of polymerizable liquid in contact with the build surface, and (ii) continuously maintaining a gradient of polymerization zone (such as an active surface) between the dead zone and the solid polymer and in contact with each thereof, the gradient of polymerization zone comprising the first component in partially-cured form. In some embodiments of CLIP, the optically transparent member comprises a semipermeable member (e.g., a fluoropolymer), and the continuously maintaining a dead zone is carried out by feeding an inhibitor of polymerization through the optically transparent member, thereby creating a gradient of inhibitor in the dead zone and optionally in at least a portion of the gradient of polymerization zone. Other approaches for carrying out CLIP that can be used in the present invention and potentially obviate the need for a semipermeable "window" or window structure include utilizing a liquid interface comprising an immiscible liquid (see L. Robeson et al., WO 2015/164234), generating oxygen as an inhibitor by electrolysis (see I. Craven et al., WO 2016/133759), and incorporating magnetically positionable particles to which the photoactivator is coupled into the polymerizable liquid (see J. Holland, WO 2016/145182), and approaches described in US Patent Application Publication No. 2018/0126630 to Panzer et al., and US Patent Application Publication No.2018/0243976 to Feller.

Further curing may be carried out subsequent to the producing step, such as by heating, microwave irradiating, contacting the object to water, contacting the object to a polymerization catalyst, irradiating the object with light at a different wavelength from that used in the producing step, or a combination thereof. Alternatively, further curing may be carried out concurrently with die producing step, such as by heating, e.g., when die producing step is an exothermic reaction that may generate heat sufficient to carry out a further curing.

Heating may be active heating (e.g., in an oven, such as an electric, gas, or solar oven), or passive heating (e.g., at ambient (room) temperature). Active heating will generally be more rapid than passive heating and in some embodiments is preferred, but passive heating— such as simply maintaining the intermediate at ambient temperature for a sufficient time to effect further cure— is in some embodiments preferred.

3. OBJECTS PRODUCED.

The methods of the present invention can be used to make a variety of useful articles having a variety of mechanical properties, including but not limited to those articles and those properties described in US Patent No. 9,598,606 to Holland et al., the disclosure of which is incorporated herein by reference.

In some embodiments, the three-dimensional (3D) object comprises a polymer blend, interpenetrating polymer network, semi-interpenetrating polymer network, or sequential interpenetrating polymer network formed from said first component and said second component

In some embodiments, the object comprises a UV -polymerized component and a polyurethane/polyurea component which are optionally interpenetrating networks, semi- interpenetrating networks, or polymeric blends.

In some embodiments, the UV -polymerized component and polyurethane/polyurea component are phase-mixed or partially phase-mixed, where these phases consist of a single, combined tanD peak, hi some embodiments, the polyurethane/polyurea component comprises soft segments and hard segments that are phase-mixed or partially phase-mixed. In some embodiments, the polyurethane phase comprises soft segments of low number average molecular weight and high number average molecular weight

In some embodiments, the polyurethane phase comprises hard segments of dissimilar backbone structure (e.g., IPDI and HMDI, IPDI and MACM).

In some embodiments, the three-dimensional object is (i) rigid, 00 semi-rigid and flexible, or (iii) elastomeric.

The three-dimensional object can be 0) uniform or symmetric in shape, or 00 irregular or asymmetric in shape.

The object may be energy absorbing with a maximum Tan Delta occurring between 0- 50°C. and wherein the Tan Delta max is greater than 0.3, when measured on a sample nominally 1 mm thick, 10 mm wide, and 10-15 mm long using a Dynamic Mechanical Analyzer with a Tension Clamp at a strain of 0.1% and at a frequency of lHz and a temperature ramp rate of 3°C/min. See, e.g., US Pat. No. 9,920,192 to Eastman Chemical.

In some preferred embodiments, the object is elastomeric and energy absorbing in nature, in which tanD maximum at lHz is from 0, 5, 10 or 15°C to 30, 35 or 40°C, and with a maximum magnitude greater than 0.3.

A material which shows increased stiffness in response to high strain rates, similar to a non-newtonian dilatant fluid, aids energy absorption/attenuation and provides more efficient energy dissipation across a greater range of impact velocities. Such increased stiffness may be accomplished in some embodiments by inclusion of hard segments in the prepolymer (such as ABPU) and/or imparted by the reacted chain extender (e.g., rigid chain extenders such as MACM, PACM, isophorene diamine, etc.).

Targeting a glass transition temperature (Tg) near the operating range of the material, when measured at 1Hz, can lead to high sensitivity to strain rate. The glass transition temperature may be adjusted, for example, with the use of mixtures in the resin components such as the reactive diluents, chain extenders, and/or prepolymers. In some embodiments, the Tg of the produced article is in a range of from 0 to 40 degrees Celsius.

Increased phase mixing and the use of higher loadings of low molecular weight soft segment (through the prepolymer(s) and/or chain extenders)) also leads to increased stiffness change at high strain rate. Phase mixing from both the UV-polymerized component and polyurethane/polyurea component, such as in an interpenetrating network or semi- interpenetrating network, is beneficial.

Embodiments of the present invention are explained in greater detail in the following non-limiting examples. EXAMPLES

Definitions:

ABPU: reactive blocked (e.g., acrylate blocked) polyurethane prepolymer

DEGMA: (diethylene glycol)methyl ether methacrylate

DUDMA: diurethane dimethacrylate

EGDMA: ethylene glycol dimethacrylate (a reactive diluent)

HDI: hexamethylene diisocyanate

IPDI: isophorone diisocyanate (Covestro Desmodur I)

IBOMA: isobomyl methacrylate

PEG600DMA: polyethylene glycol dimethacrylate with PEG unit MW approx. 600 PTMO: poly(tetramethylene oxide) diol (MW = 2900 Da)

TMP: trimethylolpropane

TBAEMA: 2-(tert-butylamino)ethyl methacrylate

LMA: lauryl methacrylate

MACM: 4,4’-methylenebis(2-methycyclohexyl-amine) (a chain extender)

PPGMA: poIy(propylene glycol) methacrylate

TMPTMA: trimethylolpropane trimethacrylate

TPO: diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (a photoinitiator)

CLIP: continuous liquid interface production

Example 1

Dual Core Resin Formulation and Use in Additive Manufacturing

The components as shown in Table 1, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINKY™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimens for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h or 175 °C for 2h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and heating rate of at a 2 °C/min. Mechanical testing results are shown below in Table 1, and a graph of TanD versus temperature is shown in Figure 1.

Example 2

Dual Cure Resin Formulation and Use in Additive Mannfactnring

The components as shown in Table 2, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINK Y™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x

10 mm x 1 mm specimens for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h or 175 °C for 2h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and heating rate of at a 2 °C/min. Mechanical testing results are shown below in Table 2, and a graph of TanD versus temperature is shown in Figure 2.

Example 3

Dual Cure Resin Formulation and Use in Additive Manufacturing

The components as shown in Table 3, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINKY™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimens for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h or 175 °C for 2h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and heating rate of at a 2 °C/min. Mechanical testing results are shown below in Table 3, and a graph of TanD versus temperature is shown in Figure 3.

Example 4

Two commercially available resins, EPU40 and RPU70 (from Carbon Inc., 10289 Mills Way, Redwood City, CA 94043 USA), were blended to generate a Tan Delta near room temperature. These two resins were dispersed at an 80:20 weight ratio of EPU40 and RPU70 and mixed by an overhead stirrer or centrifugation mixture such as THINK Y™ mixer to obtain and homogeneous resin. The resin was formed by CLIP into D638 Type IV dog-bone- shaped specimens and 35 mm x 10 mm x 1 mm specimens for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h or 175 °C for 2h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and heating rate of at a 2 °C/min. Mechanical testing results are shown below in Table 4, and a graph of TanD versus temperature is shown in Figure 4.

Example 5

Dual Cure Resin Formulation and Use In Additive Manufacturing The components as shown in Table 5, except Chain Extender, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THΊNKU™ mixer) to obtain a homogeneous resin. Then Chain Extender was added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimens for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h or 175 °C for 2h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and heating rate of at a 2 °C/min. Mechanical testing results are shown below in Table 5, and a graph of TanD versus temperature is shown in Figure 5.

Example 6

Dual Cure Resin Formulation and Use in Additive Manufacturing

The components as shown in Table 6, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINK Y™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone- shaped specimens aid 35 mm x 10 mm x 1 mm specimens for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h or 175 °C for 2h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and heating rate of at a 2 °C/min. Mechanical testing results are shown below in Table 6, and a graph of TanD versus temperature is shown in Figure 6.

Example 7

Dual Cure Resin Formulation and Use in Additive Manufacturing

The components as shown in Table 7, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINK Y™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimens for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h or 175 °C for 2h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and heating rate of at a 2 ^eC/min. Mechanical testing results are shown below in Table 7, and a graph of TanD versus temperature is shown in Figure 7.

Example 8

Dual Cure Resin Formulation and Use in Additive Manufacturing

The components as shown in Table 8, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINK Y™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimens for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h or 175 °C for 2h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and heating rate of at a 2 °C/min. Mechanical testing results are shown below in Table 8, and a graph of TanD versus temperature is shown in Figure 8.

Example 9

Dual Cure Resin Formulation and Use in Additive Manufacturing The components as shown in Table 9, except Chain Extenders, were added to a container and thoroughly mixed (either by an overhead stirrer or a centrifugation mixer such as THINK Y™ mixer) to obtain a homogeneous resin. Then Chain Extenders were added to the resin and mixed for another 2-30 min depending on the volume and viscosity of the resin. The resin was formed by CLIP into D638 Type IV dog-bone-shaped specimens and 35 mm x 10 mm x 1 mm specimens for dynamic mechanical analysis followed by thermal curing at 120 °C for 8h or 175 °C for 2h. The cured elastomer specimens were tested following ASTM D412 on an Instron apparatus and with dynamic mechanical analysis at 1 Hz and heating rate of at a 2“C/min. Mechanical testing results are shown below in Table 9, and a graph of TanD versus temperature is shown in Figure 9.

The foregoing is illustrative of the present invention, and is not to be construed as limiting thereof. The invention is defined by the following claims, with equivalents of the claims to be included therein.

Claims

What is claimed is:

1. A polymerizable liquid useful for the production of an energy absorbing three- dimensional object comprising polyurethane, polyurea, or a copolymer thereof by additive manufacturing, said polymerizable liquid comprising:

(a) a mixture of blocked or reactive blocked prepolymers (e.g., 40-90% by weight of the liquid)

(b) a polyol and/or polyamine chain extender (e.g., 5-20% by weight of the liquid)

(c) optionally a blocked or reactive blocked diisocyanate, or a blocked or reactive blocked diisocyanate chain extender,

(d) optionally a reactive diluent (e.g., 15-35% by weight of the liquid); and

(e) a photoinitiator (e.g., 0.5-2% by weight of the liquid),

wherein, the mixture of prepolymers comprise prepolymers having soft segments (e.g., polyol/polyamine midblocks) of different number average molecular weights.

2. The liquid of claim 2, wherein the mixture of prepolymers comprises:

(i) prepolymers with soft segments (e.g., a (meth)acrylate blocked polyurethane, or "ABPU") having a lower number average molecular weight of 200-900 Da; and

(ii) prepolymers with soft segments (e.g., an ABPU) having a higher number average molecular weight of 1000-10,000 Da.

3. The liquid of claim 2, wherein the prepolymers with soft segments having the lower number average molecular weight is present in the liquid in an amount of from 1% to 20% by weight

4. The liquid of claim 3, wherein the prepolymers with soft segments having the higher number average molecular weight is present in the liquid in an amount of from 15% to 45% by weight

5. The liquid of any one of claims 2-4, wherein the higher number average molecular weight ABPU midblock is 2,000 Da poly(tetramethylene oxide) and lower number average molecular weight ABPU midblock is 650 Da poly(tetramethylene oxide).

6. The liquid of any preceding claim, wherein the soft segments of the prepolymers comprise polyethers, for example, poly(tetramethylene oxide), polypropylene glycol), poly(ethylene glycol), poly(trimethylene oxide), or a copolymer of two or more thereof.

7. The liquid of any preceding claim, wherein the isocyanate for one of the blocked prepolymers in the mixture is different from the other, such as in which one is IPDI and one is HMDI.

8. The liquid of any preceding claim, wherein the chain extender comprises MACM (e.g., present at 1-10% by weight).

9. The liquid of any preceding claim, wherein the mixture of blocked or reactive blocked prepolymers is a mixture of ABPUs.

10. A polymerizable liquid useful for the production of an energy absorbing three- dimensional object comprising polyurethane, polyurea, or a copolymer thereof by additive manufacturing, said polymerizable liquid comprising a mixture of:

(a) a blocked or reactive blocked prepolymer (e.g., ABPU) having a soft segment formed from apolyol/polyamine (i.e., midblock);

(b) at least one polyol and/or polyamine chain extender;

(c) optionally, a blocked or reactive blocked diisocyanate, or a blocked or reactive blocked diisocyanate chain extender;

(d) optionally, a reactive diluent; and

(e) a photoinitiator,

wherein, one of the midblock and chain extender has a higher soft segment number average molecular weight of from 1000-10,000 Da, and the other has a lower soft segment number average molecular weight of from 200-900 Da.

11. The liquid of claim 10, wherein the chain extender is a polyether di- or triamine, and/or wherein the soft segment of the prepolymer is formed with a polyether di- or triamine.

12. The liquid of claim 10 or claim 11, wherein the chain extender has the lower number average molecular weight and is present in an amount of 1-30% by weight, and the midblock is present in an amount of 15-45% by weight.

13. The liquid of claim 10 or claim 11, wherein the midblock of the prepolymer has the lower number average molecular weight and is present in an amount of 5-40% by weight, and the chain extender is present in an amount of 5-35% by weight

14. A polymerizable liquid useful for the production of an energy absorbing three- dimensional object comprising polyurethane, polyurea, or a copolymer thereof by additive manufacturing, said polymerizable liquid comprising a mixture of:

(a) at least one constituent selected from the group consisting of: (i) a blocked or reactive blocked diisocyanate prepolymer, (ii) a blocked or reactive blocked diisocyanate, and (i) a blocked or reactive blocked diisocyanate chain extender, said consti tuent(s) comprising blocked isocyanate functional groups;

(b) at least one polyol and/or polyamine chain extender, which is present in an amount that is off-stoichiometry from the blocked isocyanate functional groups of (a);

(c) optionally a reactive diluent; and

(d) a photoinitiator.

15. The liquid of claim 14, wherein the liquid comprises a molar ratio of blocked isocyanates to polyol/polyamine chain extender of 0.75-1.25, preferably 0.8-0.95 or 1.05-1.2.

16. The liquid of any preceding claim, wherein the polymerizable liquid comprises a mixture of 2, 3, 4 or 5 different reactive diluents.

17. The liquid of any preceding claim, wherein the polymerizable liquid comprises a mixture of 2 or 3 different chain extenders.

18. The liquid of any preceding claim, wherein the three-dimensional object has a glass transition temperature in a range of from 0 to 40 degrees Celsius.

19. A method of forming an energy absorbing three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof, comprising: (a) providing a polymerizable liquid of any preceding claim, said liquid comprising: (i) a light polymerizable first component, and (ii) a second solidifiable component that is different from said first component;

(b) producing a three-dimensional intermediate from said polymerizable liquid by an additive manufacturing process including irradiating said polymerizable liquid with light to form a solid polymer scaffold from said first component and containing said second solidifiable component carried in said scaffold in unsolidified and/or uncured form, said intermediate having the same shape as, or a shape to be imparted to, said three-dimensional object;

(c) optionally cleaning said intermediate (e.g., by washing, wiping (with a blade, absorbent, compressed gas, etc.), gravity draining, centrifugal separation of residual resin therefrom, etc., including combinations thereof); and

(d) concurrently with or subsequent to said producing step (b), heating, microwave irradiating, or both, said second solidifiable component in said three-dimensional intermediate, to form said energy absorbing three-dimensional object comprising polyurethane, polyurea, or a copolymer thereof.

20. The method of claim 19, wherein said producing step (b) is carried out by stereolithography (e.g., bottom-up stereolithography such as continuous liquid interface production).

21. The method of claim 19 or 20, wherein said producing step (b) is carried out by: (i) providing a carrier and an optically transparent member having a build surface, said carrier and said build surface defining a build region therebetween; (ii) filling said build region with said polymerizable liquid, and (Hi) irradiating said build region with light through said optically transparent member to form said solid polymer scaffold from said first component and also advancing said carrier and said build surface away from one another to form said three-dimensional intermediate.

22. The method of any one of claims 19-21, wherein said step (d) is carried out subsequent to said producing step (b), and optionally but preferably subsequent to said cleaning step (c).

23. The liquid or method of any preceding claim, wherein the three-dimensional object has a Tan Delta (tanD) maximum occurring at a temperature of from 0°C to 40°C, and wherein the tanD maximum is greater than 0.3, when measured on a sample nominally 1 mm thick, 10 mm wide, and 10-15 mm long using a Dynamic Mechanical Analyzer with a Tension Clamp at a strain of 0.1% and at a frequency of lHz and a temperature ramp rate of 3°C/min.

24. The liquid or method of claim 23, wherein the three-dimensional object comprises a UV-polymerized component and a polyurethane/polyurea component, which are interpenetrating networks or semi-interpenetrating networks, wherein the polyurethane/polyurea component comprises soft segments of low number average molecular weight and high number average molecular weight

25. The liquid or method of claim 24, wherein the UV-polymerized component and a soft segment of the polyurethane/polyurea component are phase-mixed or partially phase-mixed, and wherein the polyurethane/polyurea component comprises soft segments and hard segments that are phase-mixed or partially phase-mixed.

26. The liquid or method of claim 24 or claim 25, wherein the polyurethane/polyurea component comprises hard segments of dissimilar backbone structure (e.g., IPDI and HMDI, IPDI and MACM).

27. The liquid or method of any preceding claim, wherein said three-dimensional object comprises a part of automotive damping and insulation, helmet energy absorption layer, bicycle seat, or a cushioning.

28. A three-dimensional object produced by a method of any one of claims 19-27.