CN115667181A

CN115667181A - Pre-ceramic 3D printing monomers and polymer formulations

Info

Publication number: CN115667181A
Application number: CN202080101488.0A
Authority: CN
Inventors: 扎克·埃克尔; 安德鲁·诺瓦克; 阿什利·达斯汀; 阿普里尔·罗德里格斯; 裴芳; 托拜厄斯·舍德勒
Original assignee: HRL Laboratories LLC
Current assignee: HRL Laboratories LLC
Priority date: 2020-05-30
Filing date: 2020-05-31
Publication date: 2023-01-31
Also published as: EP4157806A4; EP4157806A1; WO2021246997A1

Abstract

The present disclosure provides resin formulations that can be used for 3D printing and thermal processing to produce ceramic materials. The present disclosure provides direct, free-form 3D printing of pre-ceramic polymers, followed by conversion of the pre-ceramic polymers into 3D printed ceramic composites having potentially complex 3D shapes. Various chemical compositions are disclosed and several experimental examples are included to demonstrate the practice. For example, the pre-ceramic resin formulation may contain a carbosilane in which at least one functional group selected from the group consisting of: vinyl, allyl, ethynyl, unsubstituted or substituted alkyl, ester, amine, hydroxyl, vinyl ether, vinyl ester, glycidyl ether, vinyl amide, vinyl triazine, vinyl isocyanurate, acrylate, methacrylate, alkyl acrylate, alkyl alkylacrylate, phenyl, halogen, thiol, cyano, cyanate, or thiocyanate. These resin formulations may contain solid phase fillers to provide high thermal stability and mechanical strength (e.g., fracture toughness) in the final ceramic material.

Description

Pre-ceramic 3D printing monomers and polymer formulations

Priority data

This patent application claims priority from U.S. patent application No. 16/888,724, filed on 30/5/2020, which is hereby incorporated by reference.

Technical Field

The present invention generally relates to monomer formulations suitable for preparing pre-ceramic polymers that can be converted into ceramic matrix composites and other ceramic structures.

Background

Ceramic Matrix Composites (CMCs) overcome many of the disadvantages of conventional ceramics, such as brittle failure, low fracture toughness, and limited thermal shock resistance. Applications for ceramic matrix composites include those that require reliability (beyond the capability of metals or polymers) at high temperatures, as well as corrosion and wear resistance.

There is also a high commercial demand for ceramics for additive manufacturing (3D printing) in areas including: industrial filtration (molten metal filters, flow separators); metal working (casting of molds/blanks); implantable dental and medical devices; and semiconductor processing. Additive manufacturing of ceramic materials is also of interest for, for example, propulsion components, thermal protection systems, porous burners, micro-electromechanical systems, and electronic device packaging.

There are no mature methods for 3D printing ceramic matrix composites. Currently, CMC materials are limited to manual layup, molding, or thermoforming. There are also known techniques for sintering ceramic particles or using ceramic particles printed in a binder, both of which typically produce porous ceramics with lower strength than the parent material. Ceramic structures are typically sintered as compacted porous materials, severely limiting the geometries that can be produced.

Formulations have been described for producing ceramic materials that can be printed (additive manufacturing) by various methods such as stereolithography and laser sintering. These are typically unreinforced ceramics that do not contain a second phase and suffer from low fracture toughness. These methods are described in Zocca et al, "Additive Manufacturing of Ceramics: issues, potentialities, and Opportunities [ Additive Manufacturing of Ceramics: problem, potential and opportunity ] ", J.am.Ceram.Soc. [ journal of the American ceramic Association ],98[7] ], 1983-2001 (2015).

Additionally, formulations have been described that can produce 1D or 2D ceramics, or very small 3D structures. See U.S. Pat. No. 4,816,497 issued to Lutz et al, 3/28 1989; U.S. Pat. No. 5,698,485 issued to Bruck et al, 16/12/1997; U.S. Pat. No. 6,573,020 issued on 6/3/2003 to Hanemann et al; U.S. Pat. No. 7,582,685 issued on 9/1 of 2009 to Arney et al; and U.S. patent application publication No. US 2006/0069176A1 to Bowman et al, published on 3/30 2006.

Ceramics are difficult to process, particularly into complex shapes, compared to metals and polymers. Because they cannot be easily cast or machined, ceramics are typically consolidated from powders or deposited as thin films by sintering. Defects introduced during processing (such as porosity and inhomogeneity) determine the strength, since these defects initiate cracks and-compared to metal-brittle ceramics-have a low ability to resist fracture. This processing challenge limits the ability to take advantage of the attractive properties of ceramics, including high temperature capability, environmental resistance, and high strength. Recent advances in additive manufacturing have produced a large number of different techniques, but all additive manufacturing techniques developed for ceramic materials process only unreinforced ceramics and not ceramic matrix composites. Only a few commercially available three-dimensional (3D) printing systems provide for the printing of ceramics by selective curing of photosensitive resins containing ceramic particles, selective deposition of liquid binders onto ceramic particles (binder jetting), or selective fusing of powder beds with lasers. All of these techniques are limited by slow manufacturing rates and in many cases by time consuming adhesive removal processes. By starting with powders that need to be consolidated into dense parts, adding reinforcement without fusing or reacting the matrix and second phases, losing reinforcement capacity, and producing ceramic matrix composites is a nearly insurmountable challenge. In addition, many additive processes introduce large thermal gradients that tend to cause cracks in the ceramic. Pores, cracks, and inhomogeneities are often responsible for the low strength and poor reliability of additively manufactured ceramic parts.

Pre-ceramic polymers are a class of polymers that allow the conversion of polymeric parts into ceramic materials via heat treatment. Typically, these preceramic polymers contain silicon (Si) in the molecular backbone, where the resulting material contains Si. There are a wide variety of known pre-ceramic polymers. Examples include polysilazanes, borazine-modified hydrogenated polysilazanes, polysilanes, polycarbosilanes, silicone resins, polyvinylborazine, polyborazine (polyborazylene), and decaborane-based polymers. These preceramic polymers have been used to form specific polymer-based structures that can be subsequently heat treated (pyrolyzed or sintered) to produce near net-shape ceramic structures.

Stereolithography provides a method of building 3D polymer microstructures in a layer-by-layer process. This process typically involves a platform (e.g., substrate) lowered into the photo-monomer bath in discrete steps. At each layer, a laser is used to scan over the area of the photo-monomer to be cured (i.e., polymerized) for that particular layer. Once the layer is cured, the platform lowers a certain amount, determined by the processing parameters and the desired feature/surface resolution, and the process is repeated until a complete 3D structure is produced. An example of such stereolithography is disclosed in U.S. Pat. No. 4,575,330 issued on 11/3 1986 to Hull et al.

Improvements to the stereolithography techniques described above have been developed to improve polymer resolution through the use of laser optics and special resin formulations. In addition, improvements have been made to reduce the fabrication time of 3D polymer structures by curing the entire layer at once using a dynamic pattern generator. An example of such an improvement is disclosed in Bertsch et al, "Microterro-graphics: A Review [ Microstereolithography: review ], "Materials Research Society Symposium Proceedings," journal of the Society for Materials Research ", volume 758, 2003. Another advance in standard stereolithography techniques includes Two-Photon Polymerization methods, as disclosed in Sun et al, "Two-Photon Polymerization And 3D lithographical Microlithography [ Two-Photon Polymerization And 3D Lithographic Microfabrication ]," Advances in Polymer Science [ Polymer Science Advances ], vol.170, 169-273,2004.

There is a need for producing ceramic parts with various dimensions by 3D printing for engineering and other applications. Low cost structures that are lightweight, strong, and rigid, but can withstand high temperature oxidizing environments are sought. There is a need for a method of direct 3D printing with particle, whisker, or fiber reinforced ceramics (also referred to as ceramic matrix composite structures).

Summary of The Invention

The present invention addresses the foregoing needs in the art as will now be summarized and then further described in detail below.

Some variations provide a pre-ceramic resin formulation for 3D printing and free radical or cationic polymerization, the pre-ceramic resin formulation comprising:

(a) A functionalized carbosilane having the following chemical structure:

wherein:

R ¹ selected from the group consisting of: hydrogen, vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, alkylacrylate groups, phenyl groups, halogen groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, and combinations thereof;

R ² selected from the group consisting of: hydrogen (except when R is ¹ When hydrogen), vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, alkylacrylate groups, phenyl groups, halogen groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, and combinations thereof; and is

n =1 to 100;

(b) A photoinitiator;

(c) Optionally, a free radical inhibitor; and

(d) Optionally, 3D printing a resolution agent.

In some embodiments of the preceramic resin formulation, R ¹ Or R ² One of which is hydrogen. In some embodiments, R ¹ Or R ² Is a vinyl group or an allyl group. In some embodiments, R ¹ Or R ² Is an acrylate group or a methacrylate group (or other alkyl acrylate group). In some embodiments, R ¹ Or R ² Is a thiol group or a thiol-containing group.

The preceramic resin formulation may contain at least two different functionalized carbosilanes, each conforming to the above chemical structure, wherein R ¹ 、R ² And n is independently selected for different functionalized carbosilanes.

The photoinitiator may be present in the preceramic monomer formulation, for example, at a concentration of from about 0.001 weight percent to about 10 weight percent.

In some embodiments, upon exposure to light having a wavelength from about 200nm to about 500nm, the photoinitiator generates free radicals by intramolecular bond cleavage or intermolecular hydrogen abstraction.

For example, the photoinitiator may be selected from the group consisting of: 2, 2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methylpropiophenone, camphorquinone, bis (2, 4, 6-trimethylbenzoyl) -phenylphosphine oxide, benzophenone, benzoyl peroxide, and combinations thereof.

The free radical inhibitor may be present in the pre-ceramic monomer formulation, for example, at a concentration of from about 0.001 wt% to about 10 wt%.

For example, the free radical inhibitor may be selected from the group consisting of: hydroquinone, methylhydroquinone, ethylhydroquinone, methoxyhydroquinone, ethoxyhydroquinone, monomethyl ether hydroquinone, propylhydroquinone, propoxyhydroquinone, tert-butylhydroquinone, n-butylhydroquinone, and combinations thereof.

The 3D printing resolution agent may be present in the pre-ceramic resin formulation, for example, at a concentration of from about 0.001 wt% to about 10 wt%.

For example, the 3D printing resolution agent may be selected from the group consisting of: 2- (2-hydroxyphenyl) -benzotriazoles, 2-hydroxyphenyl-benzophenones, 2-hydroxyphenyl-s-triazines, 2'- (2, 5-thiophenediyl) bis (5-tert-butylbenzooxazoles), 2' - (1, 2-ethenediyl) bis (4, 1-phenylene) bisbenzoxazoles, and combinations thereof.

In some embodiments, the pre-ceramic monomer formulation further comprises a thermal radical initiator, such as (but not limited to) a thermal radical initiator selected from the group consisting of: benzoyl peroxide, dicumyl peroxide, 2' -azobisisobutyronitrile, and combinations thereof.

In certain embodiments, the preceramic monomer formulation further comprises a radiation triggered free radical initiator that is active at a second wavelength that is substantially different from the first wavelength at which the photoinitiator is active.

The preceramic resin formulation may further contain a cross-linking agent such as, but not limited to, a silazane.

In some embodiments, the preceramic monomer formulation further comprises from about 0.1% to about 70% by volume of a solid phase filler. Exemplary solid phase fillers include, but are not limited to, si, siC, siOC, siCN, siCBN, siOCN, siAlON, si ₃ N ₄ 、SiO ₂ Silicate glass, zirconium hydride, and combinations thereof.

Some variations of the invention provide a preceramic polymer composition comprising a functionalized polycarbosilane having the following polymer structure:

wherein:

R ¹ selected from the group consisting of: hydrogen, vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, BAn alkenyl ether group, a vinyl ester group, a glycidyl ether group, a vinyl amide group, a vinyl triazine group, a vinyl isocyanurate group, an acrylate group, an alkylacrylate group, a phenyl group, a halogen group, a thiol-containing group, a cyano group, a cyanate group, a thiocyanate group, and combinations thereof;

n =2 to 200, for example 5 to 100.

In some embodiments of the preceramic polymer composition, R ¹ Or R ² One of which is hydrogen.

The preceramic polymer composition may contain at least two different functionalized polycarbosilanes, each conforming to the above polymer structure, wherein R ¹ 、R ² And n is independently selected for different functionalized polycarbosilanes.

In some embodiments, the preceramic polymer composition comprises a functionalized polycarbosilane copolymer having the following copolymer structure:

wherein:

R ¹ 、R ² 、R ³ and R ⁴ Independent of each otherIs selected from the group consisting of: hydrogen, vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, alkylacrylate groups, phenyl groups, halogen groups, thiol groups, alkylthiol groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, mercaptopropionate groups, thioglycolate groups, aromatic groups, and combinations thereof;

R ³ and R ⁴ Is different from R ¹ Or R ² ；

n =1 to 200; and is

m =1 to 200.

In certain embodiments, the preceramic polymer composition comprises a functionalized polycarbosilane copolymer having the following copolymer structure:

wherein R is ¹ Is hydrogen, R ² Is an allyl radical, R ³ Is hydrogen, and R ⁴ Is a vinyl group. For example, the ratio of m to n may be from about 2 to about 20.

wherein R is ¹ Is hydrogen, R ² Is an allyl radical, R ³ Is an acrylate group, and R ⁴ Is hydrogen. For example, the ratio of m to n may be from about 0.1 to about 10.

wherein R is ³ May be selected from C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups. For example, the ratio of m to n can be from about 0.1 to about 10.

wherein R is ³ May be selected from C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups. For example, the ratio of m to n may be from about 0.1 to about 10.

The preceramic polymer composition may further contain a crosslinking agent such as, but not limited to, a silazane. In some embodiments, the crosslinking agent may be a monomer or oligomer of a silane having UV reactive functional groups (e.g., vinyl ether, acrylate, methacrylate, glycidyl, and/or glycidyl ether). Crosslinking agents may be used to increase the crosslink density of the polymer. In some cases, the crosslinking agent reduces the resin viscosity.

In some embodiments, the pre-ceramicThe polymer composition comprises copolymer repeat units different from polycarbosilane repeat units. For example, the copolymer repeat units may be polycarbonitrosilane (polycarbonisilane) repeat units containing nitrogen bonded to silicon and/or carbon. In certain embodiments, the nitrogen is bonded to a functional group selected from the group consisting of: hydrogen, vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, alkyl acrylate groups, phenyl groups, halogen groups, thiol groups, alkyl thiol groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, mercaptopropionate groups, thioglycolate groups, aromatic groups, and combinations thereof.

In some embodiments, the pre-ceramic polymer composition further comprises from about 0.1% to about 70% by volume of a solid phase filler. Exemplary solid phase fillers may be selected from the group consisting of: si, siC, siOC, siCN, siCBN, siOCN, siAlON, si ₃ N ₄ 、SiO ₂ Silicate glass, zirconium hydride, and combinations thereof.

The pre-ceramic polymer composition may be a 3D printed polymer, which may be heat treated to produce a 3D printed ceramic part.

Drawings

Fig. 1A is an optical microscope image (scale bar 500 μm) of the solid phase filler of SiC dispersed in the pre-ceramic silicone monomer of example 1.

Fig. 1B is an optical microscope image (scale bar 200 μm) of the solid phase filler of SiC dispersed in the pre-ceramic silicone monomer of example 1.

Fig. 2 is a photograph of the pre-ceramic polymer (right side) and the pyrolyzed ceramic part (left side) in example 2.

Fig. 3 is a graph of thermogravimetric analysis of example 2 for the pyrolysis of UV-cured preceramic polymer into pyrolyzed ceramic material, which measures the loss of sample mass over time as the pyrolysis temperature increases.

Fig. 4 is a photograph of a 3D printed polymer plate and 3D printed polymer strip of example 9.

Fig. 5 is a photograph of an amorphous SiC plate and an amorphous SiC strip in example 9.

Fig. 6 is a photograph of 3D printed polymer strips, amorphous SiC strips, and SiC strips crystallized at 1500 ℃ and 1600 ℃ in example 9.

FIG. 7 is a graph of the thermal weight loss associated with the pre-ceramic polymer when it was pyrolyzed up to 1000 ℃ in example 9.

FIG. 8 is a graph of Thermogravimetric (TG) weight loss and Differential Scanning Calorimetry (DSC) associated with preceramic polymers when pyrolyzed up to 1000 ℃ and then further heat treated to 1500 ℃ in example 9.

Fig. 9 shows the X-ray powder diffraction pattern of the ceramic material obtained from high temperature treatment at 1600 ℃ for 4 hours in argon in example 9, revealing the β -SiC phase in the crystalline ceramic material.

Detailed Description

The compositions (also known as formulations), structures, systems, and methods of the present invention will be described in detail with reference to various non-limiting examples.

This description will enable one skilled in the art to make and use the invention, and describes several embodiments, adaptations, variations, alternatives, and uses of the invention. These and other embodiments, features and advantages of the present invention will become more apparent to those skilled in the art when the following detailed description of the present invention is taken in conjunction with the accompanying drawings.

As used in this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. Unless defined otherwise, all 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.

Unless otherwise indicated, all numbers expressing conditions, concentrations, dimensions, and so forth, used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon, at least, the particular analytical technique.

The term "comprising" synonymous with "including", "containing", or "characterized by" is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. "comprising" is a term of art used in claim language that means that the specified claim element is essential, but that other claim elements can be added and still constitute a concept within the scope of the claims.

As used herein, the phrase "consisting of 8230 \8230composition does not include any elements, steps or ingredients not specified in the claims. When the phrase "consisting of (8230) \8230; composition of (or variants thereof) appears in the clause of the claim body and does not immediately follow the preamble, that phrase only limits the elements set forth in that clause; other elements are not excluded from the claims as a whole. As used herein, the phrase "consisting essentially of" \8230: "8230"; "limits the scope of the claims to specified elements or method steps, plus those that do not materially affect the basic and novel characteristics of the claimed subject matter.

With respect to the terms "comprising," consisting of, "" 8230, "" consisting of, "and" consisting essentially of, "\8230," "8230," "consisting of," when one of these three terms is used herein, the presently disclosed and claimed subject matter may include the use of either of the other two terms. Thus, in some embodiments not explicitly recited otherwise, any instance of "comprising" may be replaced by "consisting of 8230; …" consisting of "or alternatively" consisting essentially of 8230; \8230; composition of ".

Variations of the present invention provide resin formulations that can be used for 3D printing (e.g., by stereolithography) of intermediate structures followed by thermal treatment (e.g., by firing or pyrolysis) to convert the 3D intermediate structures into 3D ceramic structures. Monomer and polymer systems can be printed into potentially complex 3D shapes with high thermal stability and mechanical strength.

"Pre-ceramic" in this disclosure refers only to the ability to be ultimately converted to a ceramic material. It should be noted that the disclosed pre-ceramic resin formulations are precursors to pre-ceramic polymers, which are themselves precursors to ceramic materials. As contemplated herein, "resin" means a composition capable of polymerization or curing, further polymerization or curing, or crosslinking. The resin may include monomers, oligomers, prepolymers, or mixtures thereof.

The extremely high melting points of many ceramics, as compared to metals and polymers, pose challenges to additive manufacturing to fabricate 3D parts. Ceramics cannot be easily cast or machined. In contrast, the method of the present invention enables geometric flexibility. As described herein, pre-ceramic resins cured with Ultraviolet (UV) light in a stereolithography 3D printer or through a patterned mask, for example, form 1D, 2D, or 3D polymer structures that can have complex shapes and porous architectures. These polymer structures can then be thermally converted into corresponding 1D, 2D, or 3D ceramic parts, preferably with low shrinkage, or at least uniform shrinkage.

Some variants of the invention are based on direct, free-form 3D printing of a pre-ceramic polymer optionally loaded with a solid phase filler, followed by conversion of the pre-ceramic polymer into a 3D printed ceramic matrix composite. The monomer and polymer systems are selected to have specific properties such that they can be printed into complex 3D shapes using 3D printing methods, including stereolithography. Some embodiments provide free-form ceramic matrix composite parts containing UV-cured, 3D-printed (e.g., stereolithographically), solid-filled pre-ceramic Si-containing polymer resins, or related monomer formulations. As used herein, "polymeric resin" means a monomer, oligomer, prepolymer, or other molecule that is converted to a polymer.

The preceramic monomer formulation is designed to allow the formation of ceramic structures with preferably high thermal stability (such as chemical and physical stability at temperatures greater than 1200 ℃) and good mechanical strength (including stiffness, flexural strength, hardness, and/or fracture toughness). Among other benefits, solid phase fillers can improve mechanical properties, especially the fracture toughness of (inherently) brittle ceramic materials.

In various embodiments, the present invention is applicable to components that are additively manufactured in order to reduce part count, scrap, or non-repetitive engineering. Some embodiments are suitable for high wear or high temperature applications requiring ceramic materials. Specific applications of interest include, for example, propulsion structures (blades, impellers, nacelles, and propellers), control surfaces (fins and leading edges), hypersonic structures (thermal protection systems and heat shields), high wear parts (brakes, clutches, and rotors), catalyst support structures (e.g., catalytic converters), pump components, filters, brakes, clutches, and space probes and vehicles.

The present disclosure describes a family of resin formulations and methods for 3D printing pre-ceramic polymer parts with optional solid phase fillers, and then firing or pyrolyzing the parts into ceramic. These ceramic materials can be prepared from a wide variety of pre-ceramic monomer formulations that can be used for UV-curing based 3D printing. Stereolithography, laser rastering, digital light processing, liquid crystal device projection, two-photon lithography, or other techniques may be used for 3D printing monomer formulations.

In some variations, the monomer formulation is a mixture of a liquid pre-ceramic monomer resin and a solid phase filler. The liquid resin is preferably UV curable so as to be able to define a three dimensional shape via a 3D printing method.

It should be noted that in this disclosure, all references to "UV," "UV curable," "UV curing based," and the like shall include references not only to ultraviolet radiation, but also other bands of electromagnetic radiation that may be effective in various embodiments, including microwave radiation, terahertz radiation, infrared radiation, visible radiation (light), ultraviolet radiation, and X-rays.

(a) A functionalized carbosilane having the following chemical structure:

wherein:

R ¹ selected from the group consisting of: hydrogen, vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, methacrylate groups, alkylacrylate alkyl ester groups, phenyl groups, halogen groups, thiol groups, alkylthiol groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, mercaptopropionate groups, thioglycolate groups, aromatic groups, and combinations thereof;

R ² selected from the group consisting of: hydrogen (except when R is ¹ When hydrogen), vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, methacrylate groups, alkylacrylate groups, phenyl groups, halogen groups, thiol groups, alkylthiol groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, mercaptopropionate groups, thioglycolate groups, aromatic groups, and combinations thereof; and is

n =1 to 100;

(b) Photoinitiators (e.g., photoinitiators that generate free radicals when exposed to light and/or cationic photoinitiators);

(c) Optionally, a free radical inhibitor; and

(d) Optionally, 3D printing a resolution agent.

Typically, R ¹ And R ² Is not hydrogen, in which case the carbosilane is referred to as a "functionalized carbosilane". In a preferred embodiment, R ¹ And R ² Are not hydrogen. In some embodiments of the preceramic resin formulation, R ¹ Or R ² One of which is hydrogen. In some embodiments, R ¹ Or R ² Is a vinyl group or an allyl group. In some embodiments, R ¹ Or R ² Is an acrylate group or a methacrylate group (or other alkyl acrylate group). In some embodiments, R ¹ Or R ² Is a thiol group or a thiol-containing group.

It should be noted that no R may be present throughout the carbosilane structure ¹ Some of the repeating units of (A), do not contain R ² Or do not contain R ¹ Or R ² Some of the repeat units of (a). In various embodiments, containing R ¹ And R ² The fraction of repeating units of (a) may be at least 50%, 60%, 70%, 80%, 90%, 95%, 99%, or 100%.

When R is ¹ Or R ² One is C ₂ -C ₁₈ Unsubstituted or substituted radicals, one or more C = C bonds and/or one or more C ≡ C bonds may be present within the radical. When one C = C bond is present, the R group is a diene; when two C = C bonds are present, the R group is a triene or the like. When R is ¹ Or R ² Is a C wherein a terminal C.ident.C bond is present ₃ -C ₁₈ When unsubstituted or substituted, a propargyl group may be present. Aromatic moieties may be present, for example the R group may be or include a phenyl group (e.g., phenylvinyl, phenylallyl, etc.). C ₁ Or C ₂ Unsubstituted or substituted radicals being structurally relatedIs straight-chain, and C ₃ -C ₁₈ The unsubstituted or substituted group may be linear, cyclic, or branched.

The repeating units of the above carbosilanes can be arranged as linear repeating units, cyclic repeating units, branched repeating units, or combinations thereof. The branched repeat units themselves may be linear or cyclic. For convenience, the molecules are depicted in a linear arrangement, but are not so limited. In some embodiments, all of the n repeat units are linked in a linear chain. In some embodiments, where n.gtoreq.3, n repeating units are linked within the cyclic molecule. As contemplated herein, a "cyclic molecule" is a molecule in which at least one ring of atoms containing at least two Si-C bonds is present. In certain embodiments, some of the n repeat units are attached within a cyclic portion of the molecule and others of the n repeat units are attached within a linear portion of the molecule.

In some embodiments, R ¹ Or R ² Is a UV active functional group. As used herein, a "UV-active functional group" is a chemical group in the form of a plurality of atoms bonded together in a functional group that has absorption in the UV or visible region of electromagnetic radiation (wavelengths from about 100nm to about 700 nm). Absorption occurs when the UV active molecules absorb ultraviolet or visible light of an excited valence electron (UV activity), causing an electronic transition from the ground state to the excited state. UV absorption can be measured by a UV-visible spectrophotometer, which provides a spectrum of absorption versus wavelength. In some embodiments, the UV active functional group is selected from the group consisting of: ethynyl, vinyl, allyl, acrylate, methacrylate, vinyl ether, epoxide, oxetane, thiol, thione, isothiocyanate, and combinations, analogs, or derivatives thereof that maintain UV activity.

The preceramic resin formulation may contain at least two different carbosilanes, each conforming to the above chemical structure, wherein R ¹ 、R ² And n is independently selected for different carbosilanes.

In some embodiments, the photoinitiator is a cationic photoinitiator, such as (but not limited to) a sulfonium, iodonium, and/or ferrocenium cation paired with a non-nucleophilic anion. For example, the UV curable resin may contain a salt that generates an acid (e.g., a bronsted acid) upon light exposure by cleavage of a sulfonium, iodonium, and/or ferrocenium cation of an onium salt paired with a proton donor. Cationic photoinitiators are typically active at light wavelengths from 200nm to 350 nm. Initiators active at lower or higher wavelengths are also suitable for use in the monomer formulations. When the polymerization is or includes cationic polymerization, cationic photoinitiators can be used. Different cationic photoinitiators or photoacid generators will generally produce different polymerization rates. Combinations of different types of cationic photoinitiators, including ionic and nonionic photoacid generators, can be used in the polymerization process.

Exemplary cationic photoinitiators include, but are not limited to, sulfonium, iodonium, and ferrocenium salts; cyclopentadienyl cumene-iron hexafluorophosphate; diphenyliodonium phosphate; triarylsulfonium hexafluoroantimonate; or a combination thereof. When present, the cationic photoinitiator may be up to about 10wt% of the monomer formulation. In various embodiments, the cationic photoinitiator is about 0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1,2, 5, or 10 weight percent of the monomer formulation.

For example, the free radical inhibitor may be selected from the group consisting of: hydroquinone, methylhydroquinone, ethylhydroquinone, methoxyhydroquinone, ethoxyhydroquinone, monomethyl ether hydroquinone, propylhydroquinone, propoxyphydroquinone, tert-butylhydroquinone, n-butylhydroquinone, and combinations thereof.

The preceramic resin formulation may further contain a cross-linking agent such as (but not limited to) a silazane. In various embodiments, the crosslinking agent may be selected from the group consisting of: monovinyl silane, divinyl silane, trivinyl silane, tetravinyl silane, (meth) acryloxypropyldimethylmethoxy silane, (meth) acryloxypropylmethyldimethoxy silane, dimethyldivinyl silane, 1, 3-divinyl-1, 3-tetramethyldisilazane, 1,3,5, 7-tetravinyl-1, 3,5, 7-tetramethylcyclotetrasilazane, 1,2,3,4,5,6,7, 8-octamethylcyclotetrasilazane, and combinations thereof. In certain embodiments, the crosslinking agent is a silane and/or hydrocarbon monomer or oligomer having a UV reactive functional group (e.g., vinyl ether, (meth) acrylate, glycidyl, or glycidyl ether).

The pre-ceramic monomer formulations may be loaded with different solid materials, or multiple solid materials as solid phase fillers to form polymer composite parts that may be directly converted to Ceramic Matrix Composites (CMCs) via pyrolysis or other thermal treatments. These solid phase fillers may include fibers, whiskers, platelets, particles, nanoparticles, nanotubes, or other forms of materials that may at least partially withstand pyrolysis conditions. Exemplary solid phase fillers include, but are not limited to, carbides, oxides, nitrides, or carbon (e.g., diamond). Certain exemplary solid phase fillers include, but are not limited to, si, siC, C, al ₂ O ₃ 、SiO ₂ Mullite (Al) ₂ O ₃ -SiO ₂ )、Si ₃ N ₄ SiAlON, BN, and/or YAG (Y) ₃ Al ₅ O ₁₂ )。

In some embodiments, the preceramic monomer formulation comprises from about 0.1% to about 70% by volume of the solid phase filler. Exemplary solid phase fillers include, but are not limited to, si, siC, siOC, siCN, siCBN, siOCN, siAlON, si ₃ N ₄ 、SiO ₂ Silicate glass, zirconium hydride, and combinations thereof.

The preceramic monomer formulation may further comprise one or more surface-active agents in the form of surfactants, such as dispersing agents, emulsifiers, or wetting agents, which reduce the interfacial tension between the optional solid filler and the liquid resin, thereby facilitating mixing and dispersion of the solids within the resin matrix. The surfactant may reduce settling and aggregation of the (optional) solid filler to improve the uniformity, stability, and shelf life of the UV curable resin.

Surfactants contain a mixture of hydrophobic and hydrophilic functional groups that provide simultaneous adsorption onto multiple types of surfaces. The hydrophobic functional group may include, but is not limited to, a hydrocarbon chain, a fluorocarbon chain, a siloxane, or a carbosilane. The hydrophilic functional groups can have a range of compositions based on polarity (e.g., nonionic, anionic, cationic, or zwitterionic). Examples of surfactants include, but are not limited to, carboxylates, sulfates, sulfonates, phosphates, quaternary ammonium salts, betaines, sulfobetaines, ethoxylates, methoxysilanes, or combinations thereof. Various types of surfactants may be present.

When included in the preceramic monomer formulation, the surfactant may be present in the preceramic monomer formulation at a concentration of from about 0.001 weight percent to about 15 weight percent. In various embodiments, the surfactant is at a concentration of about 0.005 wt%, 0.01 wt%, 0.1 wt%, 0.5 wt%, 1wt%, 2 wt%, 5wt%, or 10wt% of the preceramic monomer formulation.

Some variations of the invention provide a pre-ceramic polymer composition comprising a functionalized polycarbosilane having the following polymer structure:

wherein:

R ¹ selected from the group consisting of: hydrogen, vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, alkyl acrylate groups (e.g., methacrylate, ethyl acrylate, and the like), alkyl acrylate groups, phenyl groups, halogen groups, thiol groups, alkyl thiol groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, mercaptopropionate groups, thioglycolate groups, aromatic groups, and combinations thereof;

R ² selected from the group consisting of: hydrogen (except when R is ¹ When hydrogen), vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxy groupsA group, a vinyl ether group, a vinyl ester group, a glycidyl ether group, a vinyl amide group, a vinyl triazine group, a vinyl isocyanurate group, an acrylate group, a methacrylate group, an alkylacrylate group, a phenyl group, a halogen group, a thiol group, an alkylthiol group, a thiol-containing group, a cyano group, a cyanate group, a thiocyanate group, a mercaptopropionate group, a thioglycolate group, an aromatic group, and combinations thereof; and is provided with

n =2 to 200, for example 5 to 100.

The repeating units of the above polycarbosilanes may be arranged as linear repeating units, cyclic repeating units, branched repeating units, or combinations thereof. The branched repeating units themselves may be linear or cyclic. For convenience, the polymers are depicted in a linear arrangement, but are not so limited. In some embodiments, all of the n repeat units are linked in a linear chain. In some embodiments where n ≧ 3, n repeating units are linked within the cyclic polymer. In certain embodiments, some of the n repeat units are attached within a cyclic portion of the polymer and others of the n repeat units are attached within a linear portion of the polymer.

Typically, R ¹ And R ² Is not hydrogen. In a preferred embodiment, R ¹ And R ² Are not hydrogen. In some embodiments of the preceramic polymer composition, R ¹ Or R ² One of which is hydrogen.

It should be noted that no R may be present throughout the polycarbosilane structure ¹ Some of the repeating units of (A), do not contain R ² Or do not contain R ¹ Or R ² Some of the repeat units of (a). In various embodiments, containing R ¹ And R ² The fraction of repeating units of (a) may be at least 50%, 60%, 70%, 80%, 90%, 95%, 99%, or 100%.

The preceramic polymer composition may contain at least two different polycarbosilane repeat units, each corresponding to the aboveA polymer structure wherein R ¹ 、R ² And n is independently selected for different polycarbosilane repeat units.

In some embodiments, the preceramic polymer composition comprises a polycarbosilane copolymer having the following copolymer structure:

wherein:

R ¹ 、R ² 、R ³ and R ⁴ Independently selected from the group consisting of: hydrogen, vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, alkylacrylate groups, phenyl groups, halogen groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, and combinations thereof;

R ³ and R ⁴ Is different from R ¹ Or R ² ；

n =1 to 200; and is

m =1 to 200.

For convenience, the copolymers are depicted in a linear arrangement, but are not so limited. In some embodiments, the n repeating units and the m repeating units are all linked in a linear chain. In some embodiments where n + m.gtoreq.3, there are repeat units linked within the cyclic copolymer. In certain embodiments, some of these repeat units are linked within the cyclic portion of the copolymer while other repeat units are linked within the linear portion of the copolymer.

In addition, the copolymers are depicted as block copolymers; it is to be understood that the copolymer can be, for example, an alternating copolymer or a random copolymer. For example, the alternating copolymer may containHas R ¹ And R ² And contain R ³ And R ⁴ Or may comprise a single repeat unit comprising R ¹ And R ² With a short block of repeating units containing R ³ And R ⁴ Alternating short blocks of repeating units of (a).

Since the allyl groups are vinyl-containing groups, carbosilane polymers modified with vinyl groups and/or allyl groups may be referred to as vinyl-functional polycarbosilanes. In monomeric form, carbosilane molecules modified with vinyl and/or allyl groups may be referred to as vinyl-functional carbosilanes. An exemplary synthetic route for preparing vinyl-functional carbosilanes or polycarbosilanes includes the reaction of a halosilane with a vinyl grignard reagent, an allyl grignard reagent, or a blend thereof, followed by reduction. See U.S. Pat. No. 5,153,295 issued to Whitmarsh et al, 10, 6, 1992, which is incorporated herein by reference.

wherein R is ¹ Is hydrogen, R ² Is an allyl radical, R ³ Is an acrylate group, and R ⁴ Is hydrogen. For example, the ratio of m to n can be from about 0.1 to about 10.

Carbosilane polymers modified with acrylate groups and/or alkyl acrylate groups may be referred to as acrylate-functionalized polycarbosilanes. In monomeric form, carbosilane molecules modified with acrylate and/or alkylacrylate groups may be referred to as acrylate-functionalized carbosilanes. An exemplary synthetic route for preparing acrylate-functionalized carbosilanes or polycarbosilanes involves the oxidation of silyl hydrides (silylhydrides) with acrylic acid or derivatives thereof.

Carbosilane polymers modified with thiol groups may be referred to as thiol-functionalized polycarbosilanes. In the monomeric form, the carbosilane molecules modified with thiol groups may be referred to as thiol-functionalized carbosilanes. An exemplary synthetic route for preparing thiol-functional carbosilanes or polycarbosilanes involves reacting a halosilane with thiourea in an aqueous base.

The preceramic polymer composition may further contain a crosslinking agent such as, but not limited to, a silazane. In various embodiments, the crosslinking agent may be selected from the group consisting of: monovinyl silane, divinyl silane, trivinyl silane, tetravinyl silane, (meth) acryloxypropyldimethylmethoxy silane, (meth) acryloxypropylmethyldimethoxy silane, dimethyldivinyl silane, 1, 3-divinyl-1, 3-tetramethyldisilazane, 1,3,5, 7-tetravinyl-1, 3,5, 7-tetramethylcyclotetrasilazane, 1,2,3,4,5,6,7, 8-octamethylcyclotetrasilazane, and combinations thereof.

In some embodiments, the preceramic polymer composition comprises copolymer repeat units that are different from polycarbosilane repeat units. For example, the copolymer repeat units may be polycarbonitrosilane (polycarbonitrosilane) repeat units containing nitrogen bonded to silicon and/or carbon. In certain embodiments, the nitrogen is bonded to a functional group selected from the group consisting of: hydrogen, vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, alkylacrylate groups, phenyl groups, halogen groups, thiol groups, cyano groups, cyanate groups, thiocyanate groups, and combinations thereof.

In some embodiments, the preceramic polymer composition further contains a photoinitiator that is present in the starting preceramic resin formulation and remains in the final polymer in raw or reacted form.

In some embodiments, the pre-ceramic polymer composition further contains a free radical inhibitor that is present in the starting pre-ceramic resin formulation and remains in the final polymer in the raw or reacted form.

In some embodiments, the pre-ceramic polymer composition further contains a 3D printing resolution agent that is present in the starting pre-ceramic resin formulation and remains in the final polymer in raw or reacted form.

Various additives may be added to the pre-ceramic polymer composition. For example, rheology modifiers (e.g., thickeners or diluents) can be added. Exemplary rheology modifiers include silica, alumina, kaolin, carbon black, and polyphosphates.

After pyrolysis, the ceramic material comprises an interconnected three-dimensional ceramic matrix material, such as, but not limited to, silicon oxycarbide (SiOC), silicon carbide (SiC), silicon nitride (Si) ₃ N ₄ ) Silicon oxynitride (SiON), silicon oxycarbonitride (SiOCN), silicon carbonitride (SiCN), silicon nitride boride (SiBN), boron-containing silicon carbonitride (SiBCN), boron Nitride (BN), and/or silicon carbide-zirconia composite (SiC/ZrO) ₂ )。

The pre-ceramic polymer composition may be a 3D printed polymer, which may be heat treated to produce a 3D printed ceramic part, as will be described in further detail later in this specification.

In some embodiments, the UV curable monomer formulation comprises a first molecule containing two or more unsaturated C = X double bonds or C ≡ X triple bonds (or at least one C = X double bond and at least one C ≡ X triple bond). X is selected from C, S, O, N, or combinations thereof, such that the functional groups include a C = C double bond, a C ≡ C triple bond, a,C = S, and C ≡ N. Any H atom involved in these functional groups may be substituted with other atoms (such as F or Cl), or pendant groups (such as alkyl, ester, amine, hydroxyl, or CN). The first molecule may contain different combinations of these different unsaturated bonds. A typical unsaturated bond is a C = C double bond at a terminal position of the molecule, where three hydrogen atoms are bonded to carbon atoms on the C = C bond (i.e., R-HC = CH) ₂ Where R is the remainder of the first molecule). Other examples of such functional groups include allyl, vinyl, ethynyl, vinyl ether, vinyl ester, vinyl amide, vinyl triazine, vinyl isocyanurate, acrylate, methacrylate, diene, triene, or mixtures thereof.

In some embodiments, the first molecule further comprises at least one non-carbon atom in the backbone or side chain of the first molecule. Examples of non-carbon atoms that may be used include, but are not limited to, si, B, al, ti, zn, O, N, P, S, ge, and combinations thereof. The non-carbon atom may be part of a cyclic or acyclic group or structure within the first molecule. The non-carbon atom is preferably not only a single non-carbon atom ionically bonded at one or more ends of the first molecule. In some embodiments, when X is O, the non-carbon atom is not O; or when X is N, the non-carbon atom is not N.

Examples of the first molecule include, but are not limited to, trivinylborazine; 2,4, 6-trimethyl-2, 4, 6-trivinylcyclotrisilazane; 1,3,5, 7-tetravinyl-1, 3,5, 7-tetramethylcyclotetrasilazane; 1,3, 5-trivinyl-1, 3, 5-trimethylcyclosiloxane; 1,3,5, 7-tetravinyl-1, 3,5, 7-tetramethylcyclotetrasiloxane; 2,2,4,4,6,6-hexaallyloxy-triazatriphosphine; tetraallyloxysilane; vinyl terminated polydimethylsiloxanes; tetraethyl silane; vinyl terminated polydimethylsiloxane-ethylene copolymers; divinyldimethylsilane; 1, 2-divinyltetramethyldisilane; 1, 4-bis (vinyldimethylsilyl) benzene; vinylmethylsiloxane homopolymers; methacryloxypropyl terminated polydimethylsiloxane; boron vinyl dimethyl silicon oxide; vinyl methyl siloxane-dimethyl siloxane copolymers, trimethylsiloxy terminated homopolymers; a vinyl ethoxysiloxane-propylethoxysiloxane copolymer; vinyl trimethoxysilane; trivinylmethylsilane; diallyl dimethylsilane; 1,3, 5-trisilacyclohexane; b, B 'B "-triethylalkynyl-N, N' N" -trimethylborazine; b, B' -triethylalkynyl borazine; vinylmethoxysiloxane, acryloxypropyl (methylsiloxane) homopolymer; polycarbosilane; a functionalized polycarbosilane; or a combination thereof.

When present, the first molecule may be up to about 100% by weight of the monomer formulation. In various embodiments, the first molecule is about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 95 weight percent of the monomer formulation.

In some embodiments, the UV curable monomer formulation comprises a second molecule having the structure R-Y-H, wherein Y = O, S, N, or a combination thereof. The molecule R-Y-H may provide two or more YH groups for polymerization and may be part of a cyclic or acyclic structure. Typical YH groups are SH groups, such as thiol or mercapto groups. The R group can be an organic group, such as an alkyl group, an ester group, an amine group, or a hydroxyl group, or an inorganic non-carbon containing atom or group. Examples of inorganic non-carbon atoms or groups in the second molecule include, but are not limited to, si, B, al, ti, zn, P, ge, S, O, N, or combinations thereof. The reaction rate varies depending on the different molecules utilized. In some preferred embodiments, thiols are employed in which at least half of the backbone is composed of inorganic atoms, such as silicon. Other atoms in the backbone may include oxygen, nitrogen, and/or carbon.

When present, the second molecule may be up to about 97% by weight of the monomer formulation. In various embodiments, the second molecule is about 0, 5, 10, 20, 30, 40, 50, 60, 70, 80, or 90 weight percent of the monomer formulation. The second molecule may be present regardless of the presence of the first molecule.

Exemplary second molecules include, but are not limited to, pentaerythritol tetrakis (3-mercaptopropionate); trimethylolpropane tris (2-mercaptoacetate); trimethylolpropane tris (3-mercaptopropionate); tetrakis (dimethyl-3-mercaptopropylsiloxy) silane; tetrakis (dimethyl-2-mercaptoacetoxysiloxy) silane; (mercaptopropyl) methylsiloxane-dimethylsiloxane copolymer; (mercaptopropyl) methyl siloxane homopolymer; pentaerythritol tetrakis (2-mercaptoacetate), thiol-functionalized polycarbosilanes; or a combination thereof.

In some embodiments, the UV curable monomer formulation comprises a third molecule having the structure R-Y, wherein Y is selected from an aliphatic ether, a cyclic ether, a vinyl ether, an epoxide, a cycloaliphatic epoxide, an oxetane group, or a combination thereof. The R group may be selected from organic groups such as alkyl groups, ester groups, amine groups, or hydroxyl groups, or inorganic non-carbon containing atoms or groups. Examples of inorganic non-carbon atoms or groups in the second molecule include, but are not limited to, si, B, al, ti, zn, P, ge, S, O, N, or combinations thereof. The inorganic non-carbon atom or group may be part of a cyclic or acyclic structure.

Exemplary third molecules include, but are not limited to, epoxy-functionalized dimethylpolysiloxanes and/or epoxycyclohexylethylmethylsiloxane/dimethylsiloxane. These monomers may be any part of the monomer formulation.

Specifically, when present, the third molecule may be up to about 100% by weight of the monomer formulation. In various embodiments, the third molecule is about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, or 95 weight percent of the monomer formulation. The third molecule may be present, whether the first or second molecule is present or not.

In some embodiments, the UV curable monomer formulation includes a photoinitiator that generates free radicals upon light exposure through intramolecular bond cleavage or intermolecular hydrogen abstraction. The photoinitiator may be active in the presence of light having a wavelength, for example, from about 200nm to about 500 nm. When the polymerization is or includes free radical polymerization, a photoinitiator may be used. Photoinitiators can be used to initiate polymerization when exposed to other wavelengths, such as in the visible spectrum. In certain embodiments, the light exposure is generated from light having one or more wavelengths selected from about 200nm to about 700nm, such as about 250, 300, 350, 400, 500, or 600 nm.

Different photoinitiators will generally produce different polymerization rates. Combinations of different types of photoinitiators can be used in the polymerization process. More than one photoinitiator may be included to allow, for example, multi-wavelength curing.

Examples of photoinitiators include, but are not limited to, 2-dimethoxy-2-phenylacetophenone; 2-hydroxy-2-methyl propiophenone; camphorquinone; bis (2, 4, 6-trimethylbenzoyl) -phenylphosphine oxide; benzophenone; benzoyl peroxide; a thioxanthone; dicumyl peroxide; 2,2' -azobisisobutyronitrile; camphorquinone; oxygen; nitrogen dioxide; or a combination thereof.

When present, the photoinitiator may be up to about 10wt% of the monomer formulation. In various embodiments, the photoinitiator is about 0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1,2, 5, or 10 weight percent of the monomer formulation.

In some embodiments, the UV curable monomer formulation comprises a free radical inhibitor added to the monomer formulation in an amount sufficient to inhibit unwanted polymerization of areas other than the desired print area. In embodiments employing free radical polymerization, the free radical inhibitor may improve the resolution of the desired moiety. Free radical inhibitors may also prevent shadow curing, which is generally undesirable. In addition, free radical inhibitors can improve the long-term stability of the formulation and keep the reaction kinetic parameters constant over time.

Exemplary free radical inhibitors include, but are not limited to, hydroquinone, methyl hydroquinone, ethyl hydroquinone, methoxy hydroquinone, ethoxy hydroquinone, monomethyl ether hydroquinone, propyl hydroquinone, propoxy hydroquinone, t-butyl hydroquinone, n-butyl hydroquinone, or combinations thereof. When present, the free radical inhibitor may be up to about 5wt% of the monomer formulation, such as about 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt%, 1wt%, or 2 wt% of the monomer formulation.

Optionally the formulation further comprises a radiation triggered free radical initiator active at a wavelength substantially different from the photoinitiator. When the pre-ceramic resin formulation comprises a thermal free radical initiator, optionally the formulation further comprises a radiation triggered free radical initiator.

In some embodiments, the UV curable monomer formulation includes a thermal free radical initiator that generates free radicals under high temperature conditions. The addition of a free radical thermal initiator achieves either multi-mechanism curing, i.e. both UV and thermal curing, or different polymerization reaction rates in the formulation. One or a combination of different types of thermal initiators may be used in the polymerization process.

The thermal initiator may be used to crosslink the remaining unreacted vinyl groups that are not reacted with the thiol groups or to react the vinyl groups with other available functional groups, such as methyl or hydrogen groups on the first or second molecule, resulting in a second type of reaction mechanism. Thermal post-curing after 3D printing may be performed, e.g. by heating the polymer structure up to 300 ℃.

Exemplary free radical thermal initiators include, but are not limited to, benzoyl peroxide, dicumyl peroxide, 2' -azobisisobutyronitrile, or combinations thereof. When present, the free radical thermal initiator may be up to about 10wt% of the monomer formulation, such as about 0.001 wt%, 0.01 wt%, 0.1 wt%, 1wt%, 2 wt%, or 5wt% of the monomer formulation.

In some embodiments, the UV curable monomer formulation includes a photoinitiator that is a cationic photoinitiator or photoacid generator, such as (but not limited to) a sulfonium, iodonium, and/or ferrocenium cation paired with a non-nucleophilic anion. For example, the UV curable resin may contain a salt that generates an acid (e.g., a bronsted acid) upon light exposure by cleavage of a sulfonium, iodonium, and/or ferrocenium cation of an onium salt paired with a proton donor. Cationic photoinitiators are typically active at light wavelengths from 200nm to 350 nm. Initiators active at lower or higher wavelengths are also suitable for use in these monomer formulations. When the polymerization is or includes cationic polymerization, an ionic photoacid generator can be used. Different cationic photoinitiators or photoacid generators will generally produce different polymerization rates. Combinations of different types of cationic photoinitiators, including ionic and nonionic photoacid generators, can be used in the polymerization process.

Exemplary cationic photoinitiators include, but are not limited to, sulfonium, iodonium, and ferrocenium salts; cyclopentadienyl cumene-iron hexafluorophosphate; diphenyliodonium phosphate; triarylsulfonium hexafluoroantimonate; or a combination thereof.

When present, the cationic photoinitiator may be up to about 10% by weight of the monomer formulation. In various embodiments, the cationic photoinitiator is about 0.001, 0.005, 0.01, 0.05, 0.1, 0.5, 1,2, 5, or 10 weight percent of the monomer formulation.

In certain embodiments, the UV curable monomer formulation includes a hydrogen donor that can be used, for example, to help generate a bronsted acid in the cation or to accelerate the anionic photoinitiator reaction. Exemplary hydrogen donors include, but are not limited to, tertiary amines, alcohols, ethers, esters, water, or combinations thereof. When present, the hydrogen donor may be up to about 2 wt% of the monomer formulation, such as about 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1wt%, or 1.5 wt% of the monomer formulation.

In some embodiments, the UV curable monomer formulation contains a UV sensitizer that may be used to effect a long UV wavelength reaction of the UV system with the photoinitiator, which typically absorbs at lower wavelengths. This is typically the case with cationic photoinitiators, which are generally limited to absorption of, for example, up to about 325-375 nm. The UV sensitizer interacts with UV light at higher wavelengths, typically in the 375-425nm range, and then with the photoinitiator to generate free radicals and/or bronsted acids. The UV sensitizer forms a triplet excited state upon absorption of UV light and then reacts with the photoinitiator via electron or energy transfer to generate free radicals and/or bronsted acids. This initiates photopolymerization.

The UV sensitizer may be selected from, for example, dibutoxyanthracene, diethoxyanthracene, 1-chloro-4-propoxythioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, or combinations thereof. When present, the UV sensitizer may be up to about 5wt% of the monomer formulation, such as about 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1wt%, 2 wt%, 3 wt%, or 4 wt% of the monomer formulation.

In some embodiments (including those utilizing free radical polymerization, cationic polymerization, or both), the UV curable monomer formulation includes one or more 3D printing resolution agents selected from UV absorbers, fluorescent agents, optical brighteners, or combinations thereof.

A "3D printing resolution agent" is a compound that improves print quality and resolution by including curing of the desired areas to laser or light exposure. In certain embodiments, the 3D printing resolution agent functions by absorbing light at a desired wavelength (e.g., UV light or visible light) and converting the energy to radiation at thermal energy or higher wavelengths. The use of 3D printing resolution agents improves print quality and resolution by including laser or light exposure to desired areas to cure laterally and/or vertically in the printing bath.

Exemplary 3D printing resolution agents include, but are not limited to, 2- (2-hydroxyphenyl) -benzotriazole; 2-hydroxyphenyl-benzophenone; 2-hydroxyphenyl-s-triazine; 2,2' - (2, 5-thiophenediyl) bis (5-tert-butylbenzoxazole); 2,2' - (1, 2-ethenediyl) bis (4, 1-phenylene) bisbenzoxazole; or a combination thereof. When present, the 3D printing resolution agent may be up to about 10wt% of the monomer formulation, such as about 0.001 wt%, 0.01 wt%, 0.1 wt%, 0.5 wt%, 1wt%, 2 wt%, 3 wt%, 4 wt%, 5wt%, 6 wt%, 7 wt%, 8 wt%, or 9 wt% of the monomer formulation.

Some variations provide a pre-ceramic resin formulation comprising:

(a) A first molecule comprising two or more C = X double bonds, two or more C ≡ X triple bonds, or at least one C = X double bond and at least one C ≡ X triple bond, wherein X is selected from the group consisting of C, S, N, O, and combinations thereof, and wherein the first molecule further comprises at least one non-carbon atom selected from the group consisting of Si, B, al, ti, zn, P, ge, S, N, O, and combinations thereof;

(b) Optionally a second molecule comprising R-Y-H, wherein R is an organic or inorganic group, and wherein Y is selected from the group consisting of S, N, O, and combinations thereof (Y is not yttrium in this specification);

(c) A photoinitiator and optionally a thermal free radical initiator;

(d) A free radical inhibitor; and

(e) 3D printing resolution agent.

In some embodiments, the first molecule is present, for example, from about 3 wt% to about 97 wt%, such as about 4 wt%, 5wt%, 10wt%, 15 wt%, 20wt%, 25 wt%, 30wt%, 35 wt%, 40wt%, 45 wt%, 50wt%, 55 wt%, 60wt%, 65 wt%, 70wt%, 75 wt%, 80wt%, 85 wt%, 90wt%, or 95 wt% of the formulation.

In some embodiments, the first molecule contains two or more C = X double bonds, and at least one of these double bonds is located at a terminal position of the first molecule. In some embodiments, the first molecule contains two or more C ≡ X triple bonds, and at least one of these triple bonds is located at a terminal position of the first molecule. In some embodiments, the first molecule contains at least one C = X double bond and at least one C ≡ X triple bond, and the C = X double bond is located at a terminal position, or the C ≡ X triple bond is located at a terminal position, or both the C = X double bond and the C ≡ X triple bond are located at (different) terminal positions within the first molecule. It should be noted that when a branch is present, the molecule may contain more than two terminal positions.

In the first molecule, the non-carbon atoms may be present in the backbone, in side chains, or both.

The first molecule may comprise one or more functional groups selected from the group consisting of: vinyl, ethynyl, vinyl ether, vinyl ester, vinylamide, vinyltriazine, vinyl isocyanurate, acrylate, methacrylate, diene, triene, and the like. In some embodiments, the first molecule comprises two or more such functional groups. By "analog" herein is meant that the functional groups have similar chemical and reactive properties with respect to polymerization of the pre-ceramic resin formulation.

In some embodiments where the second molecule is contained in the preceramic resin formulation, the second molecule is present, for example, from about 0.1% to about 97% by weight of the formulation, such as about 0.2%, 0.5%, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% by weight.

The second molecule may comprise one or more functional groups selected from the group consisting of: thiols, alkyl groups, esters, amines, hydroxyl groups, and functional analogs thereof. Alternatively or additionally, the second molecule may be chemically contained within one or more functional groups selected from the group consisting of: thiols, alkyls, esters, amines, hydroxyls, and the like.

When a second molecule is present, the R group may be or include an inorganic group comprising an element selected from the group consisting of: si, B, al, ti, zn, P, ge, S, N, O, and combinations thereof.

In some embodiments, at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% (mole percent) of the R groups are inorganic, i.e., free of carbon. In certain embodiments, at least 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50% (mole percent) of the R groups are specifically Si.

In the second molecule, the R group may be present in the main chain, in a side chain, or both. When the R group is inorganic, its non-carbon atoms may be the same or different from those in the first molecule.

The weight ratio of the second molecule to the first molecule can vary from about 0 to about 32, such as about 0.5, 1,2,3, 5, 10, 15, 20, 25, or 30. In some embodiments, the weight ratio of the second molecule to the first molecule is dependent on the ratio of thiol to vinyl. For example, in certain embodiments, for each vinyl group, there is at least one thiol functional group available.

As previously noted, some variations of the present invention employ a combination of free radical polymerization and cationic polymerization. In some embodiments, a pre-ceramic monomer formulation compatible with stereolithography or UV-curing 3D printing utilizes both cationic and free radical polymerization mechanisms, wherein the formulation comprises:

(a) A first molecule comprising two or more C = X double bonds or C ≡ X triple bonds, wherein X is selected from C and/or S, or from C, S, O, and/or N, and wherein the first molecule further comprises at least one non-carbon atom in the backbone or side chain selected from the group consisting of: si, B, al, ti, zn, P, ge, and combinations thereof;

(b) A second molecule comprising two or more thiol or mercapto (SH) groups, wherein the second molecule further comprises at least one non-carbon atom in the backbone or side chain selected from the group consisting of: si, B, al, ti, zn, P, S, ge, and combinations thereof (preferably at least 10wt%, more preferably at least 40wt% of the non-carbon atoms are inorganic, such as Si), and wherein the second molecule can be part of an alkyl group, an ester group, an amine group, or a hydroxyl group;

(c) A third molecule comprising two or more functional groups selected from aliphatic ethers, cyclic ethers, vinyl ethers, epoxides, cycloaliphatic epoxides, oxetanes, or combinations thereof, wherein the third molecule further contains at least one non-carbon atom in the backbone or side chain selected from the group consisting of: si, B, al, ti, zn, P, S, ge, and combinations thereof;

(d) A photoinitiator that generates free radicals by intramolecular bond cleavage and/or intermolecular hydrogen abstraction upon exposure to light having a wavelength from about 200nm to about 500 nm;

(e) A cationic photoinitiator or photoacid generator that can generate a Bronsted acid upon light exposure;

(f) A free radical inhibitor, wherein the free radical inhibitor is added to the monomer formulation in an amount sufficient to inhibit unwanted polymerization and prevent shadow curing in areas other than the desired exposure;

(g) UV absorbers, fluorescent agents, and/or optical brighteners added to the monomer formulation in an amount sufficient to improve print quality and resolution by curing areas including desired areas exposed to laser light or light;

(h) Optionally a UV sensitizer which effects a reaction of the UV system with the long UV wavelength of the photoinitiator, typically absorbing at lower wavelengths, to form a triplet excited state upon absorption of UV light, followed by electron or energy transfer to react with the photoinitiator to generate free radicals and/or bronsted acids to initiate photopolymerization; and

(i) Optionally from about 0.1% to about 70% by volume of one or more solid phase fillers as described herein.

In preferred embodiments, the UV curable monomer formulation further comprises one or more solid phase fillers. A "solid phase filler" as meant herein is a material that (a) forms at least one solid phase at 25 ℃ and 1 bar, and (b) enhances at least one chemical, physical, mechanical, or electrical property within a UV curable monomer formulation or reaction product thereof. Solid phase fillers are not only low cost diluent materials (also known as extenders) but are also important components of some of the formulations disclosed herein.

The solid phase filler may be from about 0.1% or about 1% to about 70% by volume of the monomer formulation, with the remaining majority typically being liquid phase UV curable monomer.

The geometry of the solid phase filler can be a fiber (including short fibers (1-100 microns in length) or long fibers (> 100 microns in length)), a whisker, a nanotube, a nanorod, a platelet, a microparticle having a diameter between 1 micron and 100 microns, a nanoparticle having a diameter between 1 nanometer and 1000 nanometers, or a combination thereof.

Particle size can be measured by a variety of techniques including, for example, dynamic light scattering, laser diffraction, image analysis, or sieve separation. Dynamic light scattering is a non-invasive established technique for measuring the size and size distribution of particles, typically in the sub-micron region (and the latest techniques even 1 nanometer). Laser diffraction is a widely used particle measurement technique for materials ranging in size from hundreds of nanometers to several millimeters. Exemplary dynamic light scattering Instruments and laser diffraction Instruments for measuring particle size are available from Malvern Instruments ltd, worcestershire, UK. Image analysis can be performed directly on the photomicrograph, scanning electron micrograph, or other image to estimate particle size and distribution. Finally, sieving is a conventional technique for identifying particles by size.

To increase the fracture toughness of the 3D printed part, solid phase fillers having an aspect ratio of at least 2 are preferred, such as fibers, whiskers, nanotubes, and nanorods. Here, "aspect ratio" is the ratio of the average length to the average width, or in the case of an arbitrary shape, the ratio of the average maximum length dimension to the average minimum length dimension. In certain embodiments, the solid phase filler aspect ratio is preferably at least 5, more preferably at least 10.

The solid phase filler composition is preferably stable at a pyrolysis temperature of at least 800 ℃ so as not to crack, melt, or vaporize during subsequent conversion of the preceramic polymer into a ceramic material. It should be noted that the solid phase filler may react with other components present in the monomer formulation or reaction products thereof (e.g., polymers) or with the furnace atmosphere gases at the pyrolysis temperature. It is possible that during high temperature processing, a portion of the solid phase filler reacts into a gas or liquid phase.

In certain embodiments, the solid phase filler precursor is introduced into the monomer formulation, where the precursor is in the liquid phase or is, for example, a gel. The solid phase filler precursor can then react or undergo a phase change, such as during polymerization, to convert the solid phase filler precursor to a solid phase filler.

The solid phase filler may have a wide range of compositions. For example, the solid phase filler composition may include, but is not limited to, silicon-based ceramics, such as SiOC, siO ₂ 、SiCN、SiC、SiCBN、SiOCN、Si ₃ N ₄ Silicate glass, and the like. The solid phase filler composition may comprise a non-silicon based ceramic, such as a metal oxide, e.g. Al ₂ O ₃ 、ZrO ₂ 、TiO ₂ Or Y ₃ Al ₅ O ₁₂ . The solid phase filler composition may include carbon-based high temperature materials such as carbon, graphene, diamond, and metal carbides, e.g., tiC, zrC, hfC, or B ₄ C. The solid phase filler composition may include a nitride based ceramic such as BN, tiN, zrN, or AlN.

Solid phase fillers interact with UV light according to Snell's law and the well-known Fresnel equation. These physical laws determine the fraction of light that is reflected, transmitted, or absorbed as the UV light passes from the resin to the filler. For UV-based 3D printing methods, it is preferable that the filler does not absorb too much UV light to prevent complete UV curing of the resin. To avoid excessive absorption of UV light, low levels of solid phase fillers may be employed, such as less than 10 volume percent of relatively small (e.g., 10 microns or less) particles. Alternatively or additionally, solid phase fillers that transmit UV light to some extent and pass UV light through may be employed. Another way to ensure that the UV light is not absorbed too much by the filler particles is to use particles having surfaces that reflect UV light. For example, aluminum reflects UV light well. The surface of such particles should be smooth for maximum reflection. A surface treatment or coating may be applied to render the surface of the filler particles reflective-such as a thin coating of aluminum or silver.

In some embodiments, the preferred solid phase filler particles are alumina (Al) ₂ O ₃ ) Quartz (SiO) ₂ ) Glass, silicon nitride (Si) ₃ N ₄ ) Yttrium Aluminum Garnet (YAG), or Boron Nitride (BN) because these materials transmit at least some UV light. SiC or C fibers absorb too much UV light and should therefore be coated with a reflective coating to achieve efficient 3D printing.

Depending on the chemistry and viscosity of the monomer formulation (resin), the solid phase filler may be treated to increase the compatibility of the solid phase filler with the resin and wetting of the resin, solubility and dispersibility of the filler in the resin, and/or bonding between the filler and the resin. In some embodiments, the dispersing aid can be selected to match the isoelectric point of the solid phase filler particles and the chemistry and functionality of the monomer resin.

Some embodiments employ surfactants having a component bound to the surface of the filler and a component dissolved in the resin system. Surface functionality can be added to the surface of a solid phase filler by covalently bonding functional groups to the surface of the filler. Examples include the use of silane surface modifiers having reactive groups that can react with the chemical components of the resin or increase the wettability and dispersibility in solid fillers. These include the addition of, for example, mercaptotrimethoxysilane, vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, or combinations thereof. The surface may also be modified by other chemical means, such as gas-solid reactions or liquid-solid reactions, for example oxidation in an oven or acid or base treatment.

For 3D printing and curing of resins, it may also be advantageous if the solid phase filler itself is coated or surface treated with a chemical containing functional groups that aid in the polymerization or crosslinking of the resin upon UV and/or heat exposure. Such functional groups include unsaturated ethers, vinyls, acrylates, methacrylates, cyclic ethers, epoxides, oxetanes, amines, hydroxyls, isocyanates, hydrides, or combinations thereof. By adding functional groups to the surface of the solid filler, fewer or even no functional groups are needed in the resin and the system can still be cured by UV exposure. Alternatively or additionally, the functional groups introduced to the surface of the solid phase filler particles may effect thermal curing after the initial UV curing during 3D printing.

The solid filler may be coated to prevent environmental degradation during pyrolysis. Reactive species, such as oxygen radicals and other free radicals, may be generated during pyrolysis. Such radicals may react with the filler and reduce its properties. To reduce this, the filler may be coated with a thin layer of protective material (such as BN) or a sacrificial material that preferentially decomposes during pyrolysis (such as pyrolytic carbon).

To increase the fracture toughness of 3D printed ceramic matrix composites, high aspect ratio fillers (e.g., fibers) may be coated with a filler/matrix interface coating. The purpose of this coating is to provide a weak filler-matrix interface that prevents matrix cracks from penetrating the filler-thereby providing damage tolerance (toughness) to the composite. The interfacial coating is preferably chemically and mechanically stable during processing and pyrolysis. Examples of interface coatings include BN, C, alN, or a combination thereof.

The formulations disclosed herein can be 3D printed using a number of different methods. In some variations, the formulations can be directly 3D printed and converted into free-form ceramic matrix composite structures. The 3D printed pre-ceramic polymeric material can be prepared directly from a pre-ceramic monomer formulation without intermediate steps. The 3D printed ceramic material can then be prepared directly from the 3D printed pre-ceramic polymer material without intermediate steps.

Preferred methods may include stereolithography, adhesive jetting, resin jetting with fiber placement, multiple jetting (polyjetting), extrusion printing, or combinations thereof.

In stereolithography, a solid phase filler is dispersed in a liquid resin (monomer formulation). The layers are cured from the top or bottom using, for example, UV laser gratings, projection micro-stereolithography, digital light projection, or liquid crystal device projection. Depending on the material selection, smaller filler sizes are preferred because filler size often limits resolution.

In general, the "jetting" of material means the selective deposition of droplets of build material onto a build bed to create a three-dimensional object. Spraying can be performed, for example, by liquid deposition, vapor deposition, or liquid-aerosol deposition via spraying (e.g., via a nozzle in communication with the material under pressure), impingement (e.g., via a tube or conduit in communication with the pumped material), or other means.

In adhesive jetting, layers of solid phase filler are spread out and a resin (monomer formulation) is jetted over the selected locations and cured, such as via UV light or thermally. This process is similar to the conventional adhesive spray method, but uses a pre-ceramic monomer formulation rather than an adhesive. Based on the monomers selected, the solid phase filler can be initially dispersed, for example, on a substrate or on a region of a polymer. After the initial step of adhesive jetting, another layer of solid filler may be dispersed on the 3D printed polymer layer, followed by resin jetting and curing. This process can be repeated many times for larger parts.

In resin injection with fiber placement, solid phase fillers in the form of long or short fibers are placed in preferred locations and aligned in preferred directions. Subsequently, the pre-ceramic resin (monomer formulation) is sprayed in the selected location and cured. The process is repeated layer by layer to build the part. Resin jetting with fiber placement allows printing of parts with high volume fractions (e.g., 30-60 vol%) of aligned fibers, resulting in improved mechanical properties (after pyrolysis) of the final ceramic structure.

In multiple jetting, a mixture of liquid resin (monomer formulation) and solid filler is jetted and the desired pattern is written. As the mixture is dispensed, it is exposed to UV light, such as a laser, LED, or plasma source, and cured to a polymer. Multiple mixtures can be dispensed through different nozzles, allowing more than one type of monomer-filler mixture to be utilized simultaneously. This results in specific mechanical properties of the final ceramic structure (after pyrolysis).

In extrusion printing, the resin and filler mixture is extruded through a micro-nozzle or micro-nozzles and cured via UV light. One advantage is that high aspect ratio fillers can be aligned by an extrusion process. Alignment generally improves the mechanical properties in the direction of alignment.

After 3D printing the part using any of the above methods, or another method, the part may be post-cured. An optional thermal post-cure is performed on the 3D polymer after 3D printing but before pyrolysis to produce a ceramic structure. A post-curing step may be employed, for example, to crosslink unreacted functional groups. Post-curing can be achieved by additional UV exposure and/or thermal post-curing in an oven at elevated temperatures (e.g., 60-500 ℃) for about 10 minutes to about 8 hours. When performing thermal post-curing, it may be beneficial to include a thermal initiator in the initial 3D printing composition to facilitate subsequent thermal curing.

Typically but not necessarily, the monomer formulation is delivered (printed) to the area of interest, such as via stereolithography, adhesive jetting, resin jetting with fiber placement, multi-jetting, or extrusion printing, followed by polymerization or polymerization occurring simultaneously with printing. Preferably, the polymerization and 3D printing steps are performed simultaneously at the desired location (e.g., layer) of the part. In some embodiments, the aggregation and 3D printing steps are performed semi-simultaneously, where multiple steps are performed in total, while at each step, an amount of aggregation and an amount of 3D printing occur. In some embodiments, it is also possible to first polymerize the pre-ceramic resin formulation, followed by 3D printing of the already prepared polymer — especially when the polymer is a thermoplastic material.

In some embodiments, curing or converting the pre-ceramic resin formulation to a pre-ceramic polymer comprises crosslinking. Crosslinking is a bond that links one polymer chain to another polymer chain. The cross-links may be covalent or ionic. When polymer chains are linked together by cross-linking, they lose their ability to move as part of the individual polymer chains. Crosslinking is a characteristic property of thermoset plastic materials. In most cases, crosslinking is irreversible unless ionic bonds are employed in reversible crosslinking (see, e.g., commonly owned U.S. patent application No. 15/391,749, filed 2016, 12, 27, which is hereby incorporated by reference).

In some embodiments, a gel is first formed when converting monomers to polymers. After gel formation, the chains crosslink together to form a solid material as the monomer conversion increases further. A "gel" is a solid jelly-like material that may have properties ranging from soft and weak to hard and tough. When in a stable state, the gel does not exhibit flow. Gels are mostly liquids by weight, but they also behave like solids due to the three-dimensional cross-linked network within the liquid.

Some variations of the invention utilize self-conducting polymer waveguides, as described in: commonly owned U.S. Pat. No. 7,687,132 issued on 30/3/2010 to Gross et al; U.S. Pat. No. 9,341,775 to Eckel et al, 2016, 5, 17; U.S. Pat. No. 9,377,567 to Jacobsen et al, 2016, 6, 28; and U.S. patent No. 9,528,776 to Roper et al, 2016, 12, 27, which is hereby incorporated by reference. Without being bound by theory or speculation, it is hypothesized that initial exposure of the monomer to a collimated beam of light may initiate microgel spots within the liquid monomer layer. These microgel dots have a higher crosslink density than the surrounding monomer/polymer, which results in a higher local refractive index. The higher refractive index at the microgel spot may act as a lens. The focused energy from the incident beam results in the formation of an initial "waveguide" in the direction of the incident (primary) beam, where the refractive index of the waveguide is higher than the surrounding monomer/polymer. U.S. patent No. 7,382,959 issued on 3/6/2008 to Jacobsen is hereby incorporated by reference herein for its description of mechanisms involving the formation of self-conducting polymer waveguides.

In exemplary embodiments, sufficient polymerization inhibitor and UV absorber are added to the resin formulation in order to confine polymerization to the laser exposure point and minimize scattering, thereby maintaining fidelity of the features of the printed part. The UV light is then scanned across the entire resin surface to expose the cross section and build up a thin slice of the part to be fabricated. While in principle any geometry can be made with this method, this method can be slow because each thin layer must be exposed individually.

Structures such as lattices and honeycombs with linear features extending from the exposed surface can be formed much faster when utilizing self-propagating light conducting polymer waveguide technology. The monomers are selected to promote a change in refractive index upon polymerization, which results in internal reflection of the UV light, thereby trapping it in the formed polymer. This utilizes a self-focusing effect, which forms a polymer waveguide, directing light towards the tip of the waveguide and causing it to further polymerize. The need for additives to control scattering and UV absorption is reduced. The architecture of the material or structure may then be defined by a patterned mask defining areas exposed to, for example, a collimated UV light source. The polymer crosslink density depends on the exposure parameters and can be increased by heat treatment or additional UV exposure. Unpolymerized resin can be recycled and reused.

Direct near-net shape conversion of the pre-ceramic 3D printed polymer to a ceramic structure may be achieved by pyrolysis or other thermal treatments such as, but not limited to, sintering, annealing, or calcining. Typically, thermal processing is based on heating the 3D printed structure under various inert or reactive atmospheres for extended periods of time (e.g., from 10 minutes to 1 week).

The heat treatment may be carried out in various atmospheres (including but not limited to N) ₂ Ar, he, air, CO ₂ 、CH ₄ 、C ₂ H ₆ 、C ₂ H ₄ 、NH ₃ Or a combination thereof) for an extended period of time. The processing pressure may vary, for example, from about 1atm to about 20 atm. Vacuum pyrolysis may also be employed, wherein the process pressure is less than 1atm, also under various atmospheres as indicated above.

Pyrolysis or other heat treatment may include heating from ambient temperature to an elevated temperature of from about 500 c to about 1500 c (e.g., from about 800 c to about 1100 c) at a heating rate of 0.1-20 c/min. These slow heating rates are preferred to allow the evolved gases to escape, thereby minimizing porosity in the final part. When porosity is desired, higher heating rates (e.g., greater than 20 deg.C/min) can be employed. Pyrolysis or other heat treatment may also include residence at an elevated temperature (e.g., 950 ℃) for at least 1, 5, 10, 15, 30, or 60 minutes. After pyrolysis, the material may be cooled back to ambient temperature at a cooling rate (of the order of magnitude) of 0.1-20 ℃/min. In some embodiments, faster cooling (e.g., on the order of greater than 20 ℃/min) is desired, for example, to freeze the desired microstructure.

The heat treatment is preferably performed after polymerization and any (optional) thermal post-curing of the 3D polymer. In certain embodiments, the heat treatment is combined with polymerization, thermal post-curing, or both (i.e., coincident in time and/or temperature). It will also be appreciated that even when sequential operation is contemplated, some amount of ceramic formation may occur prior to the planned steps of heat treatment due to the inherent kinetics and thermodynamics of the reaction system.

In some embodiments, reactive heat treatment is performed in which the gas initially present is reactive with the initial polymer, the final ceramic material, or both. When the gas is reactive, it can react with the component and cause it to leave the material. Alternatively or additionally, the gas may react with the component and remain with the base material. It is also possible that the gases react and form products, some of which exit from the material while the rest remains with the material. The reactive gas may be selected from O ₂ 、O ₃ Air, CO ₂ 、H ₂ 、H ₂ O、CH ₄ 、SO ₂ 、H ₂ S、NH ₃ 、NO、NO ₂ And N ₂ O, and the like. The maximum temperature of the reactive heat treatment may be, for example, about 300 ℃ to about 1500 ℃. The system pressure may also be adjusted to affect the gas atmosphere.

Pyrolysis or other heat treatment processes produce ceramic parts or ceramic matrix composites that may comprise various ceramic materials, such as, but not limited to, siC, siOC, si ₃ N ₄ SiON, siCN, siOCN, siBN, siBCN, BN, or combinations thereof. The composition of the ceramic part or ceramic matrix composite is obviously directly dependent on the composition of the starting 3D printing monomer formulation as provided in the present disclosure. When carbon is required in the ceramic material, it may be added, for example, by adding to the side chain of the polymerThe carbon fraction is adjusted by adding phenyl groups or by using a carbon-based crosslinking agent such as divinylbenzene.

In some embodiments, the final ceramic structure is lightweight, strong, and rigid — but can withstand high temperature oxidizing environments. The configuration and microstructure of the preceramic polymer determine the composition, microstructure, and yield of the ceramic material after heat treatment. A high crosslinking density is preferred in order to prevent cracking and loss of low molecular weight species that are not completely converted to ceramic or evolved gases during heat treatment.

During the heat treatment, gases escape, whether inert or reactive heat treatment techniques are employed. During the conversion of the preceramic polymer into a ceramic structure, gases are formed by decomposition reactions of the polymer, photoinitiator, free radical inhibitor, and/or 3D printing resolution agent. The evolved gas or vapor may include, but is by no means limited to, CH ₄ 、H ₂ 、CO、CO ₂ 、H ₂ O、SO ₂ 、H ₂ S、CH ₃ And S and the like.

Because various gases escape during pyrolysis or other thermal processing, the concentration of solid phase filler will typically be higher in the final ceramic material as compared to the starting 3D printed monomer formulation. This is because solid phase fillers are typically very stable during heat treatment and do not lose much, if any, mass, whereas polymers typically lose a significant amount of mass in pyrolysis (see, e.g., fig. 3). Thus, the concentration of solid phase filler may be greater than 70 volume percent in the final ceramic structure. In various embodiments, after heat treatment and any post processing (e.g., washing), the concentration of the solid phase filler is from about 0.1 vol% to about 90 vol%, such as about 0.5 vol%, 1 vol%, 5 vol%, 10 vol%, 20 vol%, 30 vol%, 40 vol%, 50 vol%, 60 vol%, 70 vol%, or 80 vol%, based on the total ceramic structure.

In some variations of the invention, an active solid phase functional additive is employed as the solid phase filler. By "solid phase functional additive" is meant a material that (a) forms at least one solid phase at 25 ℃ and 1atm, and (b) performs or enhances at least one chemical, physical, mechanical, electrical, or magnetic function within the ceramic structure and in the final structure at the time the ceramic structure is formed.

It should be noted that the solid phase functional additive is distinguished from the solid phase filler disclosed above. The solid phase functional additive is effective in improving the final ceramic structure compared to the solid phase filler by one or more changes specifically induced by the additive during pyrolysis or other heat treatment, as will now be described.

The solid phase functional additive may be present at from about 0.1% and about 70% by volume of the monomer formulation, with the remainder largely being liquid UV curable resin. The solid phase functional additives are geometrically dissimilar. In some embodiments, the solid phase functional additive is a small particle having an average size (length or effective diameter) from 5 nanometers to 5 micrometers.

In some embodiments, the solid phase functional additive is effective to expand in volume and resist shrinkage of the resin, thereby eliminating or reducing overall shrinkage during conversion of the polymer to a ceramic. This addresses a significant disadvantage in the art.

Specifically, upon conversion from polymer to ceramic, a linear dimensional shrinkage of about 20-30% and a mass loss of about 20-60% are typically observed. Shrinkage promotes cracking and deformation, and limits the achievable part dimensions and tolerances. Shrinkage of the pre-ceramic polymer is counteracted by the introduction of an active solid phase functional additive that expands in volume during pyrolysis. The overall shrinkage during the conversion of the polymer to ceramic can be reduced or even eliminated.

It should be noted that the solid phase functional additive is not necessarily stable (non-reactive) at pyrolysis temperatures. In many cases, it is desirable that the functional additive be reactive.

In particular, the solid phase functional additive may react directly with the pre-ceramic resin upon heat treatment. Alternatively or additionally, the solid phase functional additive may react with species (e.g., oxygen, nitrogen, or carbon) generated by decomposition of the polymer during pyrolysis. Alternatively or additionally, the solid-phase functional additive may react with the pyrolysis atmosphere (e.g., nitrogen, methane, or ammonia atmosphere) during pyrolysis. To counteract the adverse effects of shrinkage, it is preferred that these reactions occur simultaneously with the pre-ceramic resin shrinkage, or effectively reverse the volume reduction.

Examples of solid phase functional additives for counteracting resin shrinkage include, but are not limited to, scandium, yttrium, titanium, zirconium hydride, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, zinc, boron, aluminum, gallium, silicon, germanium, phosphorus, or combinations thereof. Combinations of these elements (e.g., titanium silicide, chromium silicide, magnesium silicide, zirconium silicide, or molybdenum silicide) may be used as the solid phase functional additive. Preferred solid phase functional additives in this category include aluminum, titanium, zirconium, titanium silicide, chromium silicide, magnesium silicide, and zirconium silicide.

In some embodiments, the solid phase functional additive effectively binds sulfur. For example, the solid phase functional additive can react with sulfur from thiol groups in the resin and incorporate the sulfur into the stable compound. One preferred class of UV curable pre-ceramic resins for 3D printing is based on thiol-ene reactions (olefin hydrosulfiding reactions). The thiol groups contain sulfur that may partially remain in the ceramic after pyrolysis, resulting in an unpleasant odor. Residual sulfur may also corrode metals.

To mitigate the negative effects of residual sulfur, active solid phase functional additives can be added that react with and bind the sulfur in stable compounds that are neutral in odor and neutral to corrosion of metals. Examples of solid phase functional additives for binding to sulfur include, but are not limited to, ti, zr, hf, si, al, cr, nb, crSi ₂ 、TiSi ₂ Or a combination thereof. The preferred solid phase functional additive for sulfur accumulation/scavenging is a reaction to form the stable compound Ti, respectively ₂ S ₃ 、ZrS ₂ And HfS ₂ Ti, zr, and Hf.

In some embodiments, the ceramic structure contains from about 0.01 wt% to about 20wt% sulfur, such as from about 0.1 wt% to about 10wt% sulfur. In various embodiments, the ceramic structure contains about 0.1 wt%, 0.2 wt%, 0.5 wt%, 1wt%, 2 wt%, 3 wt%, 4 wt%, 5wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt% sulfur. From about 10wt% to about 100 wt% (e.g., about 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, or 90 wt%) of the sulfur present may be combined with the solid phase functional additive in the sulfur-containing stabilizing compound.

In some embodiments, the solid phase functional additive effectively seeds the preferred ceramic phase by allowing epitaxial growth of the preferred phase without a nucleation barrier. After pyrolysis of the preceramic polymer, an amorphous ceramic is generally obtained. To increase strength and hardness and reduce high temperature creep, the amorphous ceramic material then needs to crystallize into the preferred ceramic phase. This is typically achieved by performing a long (many hours) heat treatment at a temperature above the pyrolysis temperature (either immediately after pyrolysis or as a different second heat treatment).

In contrast, with appropriate solid phase functional additives in the resin, crystallization can be promoted by seeding. Without limitation, the mechanism may include providing a surface for epitaxial growth of the preferred phase or phases of the ceramic.

For example, crystallization of β -SiC in amorphous SiC or SiCN ceramics derived from polycarbosilane-based or polysilazane-based resins can be promoted by small (e.g., 1 nanometer to 5 micrometers) β -SiC crystals. Crystallization in such resins may be carried out at temperatures between 1300 ℃ and 2800 ℃ over a period of 5 to 50 hours. Similarly, amorphous Si derived from polysilazane-based resins ₃ N ₄ Or Si in SiCN ceramic ₃ N ₄ Can be crystallized through small (e.g., 50 nanometers to 5 microns) alpha-Si, respectively ₃ N ₄ Or beta-Si ₃ N ₄ Crystals are used to facilitate this. Other crystals may be selected to promote crystallization, with typical constraints on epitaxial growth on one crystal plane having low lattice stress.

The ceramic structure may be characterized by at least 50% theoretical density, preferably at least 75% theoretical density, and morePreferably at least 95% of theoretical density. "theoretical density" refers to the actual density of the ceramic structure as a percentage of the theoretical density of the material itself, calculated in the absence of porous voids. For example, from a material having a density of 2.1g/cm ³ Has an inherent (bulk) density of 2.0g/cm ³ The absolute density of (a) shows a theoretical density of 2.0/2.1= 95%.

In various embodiments, the ceramic structure is characterized by a theoretical density of about (or at least about) 50%, 60%, 70%, 75%, 80%, 85%, 90%, or 95%. In certain embodiments, without limitation, the ceramic structure is a fully dense monolith, meaning that the ceramic structure has at least 99% (e.g., substantially 100%) of theoretical density associated with a portion or continuous region of material (also referred to as a "monolith"). In g/cm ³ The absolute density in units will vary depending on the choice of base material; an exemplary range is about 1g/cm ³ To about 4g/cm ³ 。

The overall mass loss associated with the conversion of the preceramic polymer into a ceramic structure can vary widely, such as from about 1wt% to about 90wt%, for example about 5wt%, 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, 70wt%, or 80wt%. The overall mass loss will be determined by the starting formulation (e.g., organic versus inorganic fraction) as well as by the process parameters. In principle, the lost mass can be recovered separately and used for other purposes.

A concern with mass loss may be shrinkage of the pre-ceramic polymer as it is converted into a ceramic structure. The linear shrinkage (calculated in a single dimension such as the height of the part) may be, for example, from 0% to about 60%. It should be noted that the mass loss and shrinkage are not necessarily correlated. In some embodiments, there is not much (if any) shrinkage at the expense of high quality. These embodiments tend to produce higher porosity and therefore lower density. In some embodiments with a high mass loss, there is significant shrinkage unless certain solid phase fillers are utilized as described above and/or solid phase functional additives are utilized as described below. These embodiments tend to produce lower porosity, or no porosity, and thus higher density (e.g., fully dense ceramic materials). Finally, in some embodiments, there is little mass loss, but shrinkage associated with the chemical reaction occurs. These embodiments also tend to produce relatively high densities.

The overall shape (relative geometry) of the pre-ceramic 3D printed polymer may remain in the final ceramic structure despite shrinkage, if any. That is, when shrinkage is uniform in all dimensions, the geometric features are preserved in the part: it is a scaled down version in all three dimensions. In some embodiments, the shrinkage is about uniform, meaning that the geometric features are substantially maintained with slight deviations. Uniform shrinkage is possible when there is no random cracking during the transformation of the pre-ceramic polymer into a ceramic structure, and when the reaction and gas evolution are isotropic within the material. It should be noted that in an otherwise uniform shrinking process, very small features, such as at the nanometer scale, may not be preserved.

In fact, uniform shrinkage (or no shrinkage, in certain embodiments employing active functional additives) can result in a part that is "net-shaped" or "near-net-shaped". By "net shape" is meant that the geometric features are preserved such that the part being manufactured allows for final manufacture that matches the intended design with little or no post-machining. By "near net shape" is meant that the geometric features are not completely retained, but only minimal post-processing or manual handling is required. Both net and near net shape parts require little or no machining, polishing, bonding, surface finishing, or assembly.

The density of the final ceramic part may vary, as explained above. Generally (without limitation), a range of from about 0.1g/cm may be produced ³ To about 5g/cm ³ Absolute density of (d). Fully dense ceramics may have, for example, from about 1g/cm ³ To about 4g/cm ³ The density of (c).

The strength of the final ceramic material will vary depending on the initial pre-ceramic resin formulation and the processing parameters. In some embodiments, the final ceramic material is characterized by a Young's modulus of at least about 200GPa, 300GPa, 400GPa, 500GPa, or greater, as measured at 25 ℃. In some embodiments, the final ceramic material is characterized by a flexural strength of at least about 300GPa, 400GPa, 500GPa, or greater, as measured at 25 ℃. In some embodiments, the final ceramic material is characterized by a hardness of at least about 10GPa, 20GPa, 30GPa, or greater, as measured at 25 ℃.

The engineering strength of the ceramic part will also depend on the geometry-such as the micro-truss produced by some embodiments employing self-conducting polymer waveguide technology. It should be noted that, for example, the silicon oxycarbide microlattice and honeycomb porous materials made by the method of the present invention exhibit greater strength than ceramic foams having similar densities.

The thermal stability of the final ceramic material will vary primarily depending on the initial pre-ceramic resin formulation and processing parameters. In various embodiments, the final ceramic material is thermally stable at a temperature of at least 1500 ℃, 1600 ℃, 1700 ℃, 1800 ℃, 1900 ℃, or 2000 ℃. Thermal stability means at least that the ceramic material does not melt at these temperatures, and it is also preferred that the ceramic material does not react (e.g., by oxidation or reduction), undergo thermal shock, or physically decompose (introduce defects) at these temperatures. In some embodiments, for example, the ceramic structure is characterized by being stable in the presence of air at a temperature of about 1000 ℃, 1100 ℃, 1200 ℃, 1300 ℃, 1400 ℃, 1500 ℃, 1600 ℃, 1700 ℃, 1800 ℃, or higher.

Even when machining, polishing, bonding, surface finishing, or assembly is not required, the final ceramic structure may be subjected to coloring (e.g., with ink or dye), stamping, or other non-functional features, if desired.

Examples of the invention

Example 1: preparation of 3D printing compositions for SiC/SiOC UV cured ceramic matrix composites.

A monomer mixture containing 100 parts vinylmethoxysiloxane polymer, 100 parts (mercaptopropyl) methylsiloxane polymer, 0.5 parts 2, 2-dimethyl-2-phenylacetophenone, 0.15 parts t-butylhydroquinone, and 0.25 parts 2,2' - (2, 5-thiophenediyl) bis (5-t-butylbenzooxazole) (all parts by weight) was thoroughly blended to ensure that the components were well mixed and that the mixture was a homogeneous system. The resin is capable of forming a silicon oxycarbide (SiOC) ceramic phase when polymerized and heat treated.

Then 25% by weight of silicon carbide (SiC) powder having a particle size of 50 μm was blended and subjected to ultrasonic treatment to disperse SiC particles into the above resin. The SiC microparticles act as solid phase fillers in the formation of the SiOC resin. The mixture is then ready for use as a monomer formulation in UV-cured 3D printing.

Optical microscope images of the solid phase fillers of SiC dispersed in the pre-ceramic silicone matrix are shown in fig. 1A (scale bar 500 μm) and fig. 1B (scale bar 200 μm).

Example 2: production of 3D printed UV cured SiC/SiOC ceramic matrix composites.

The monomer formulation of example 1 was 3D printed and UV cured, followed by thermal treatment to form a ceramic matrix composite. The monolithic part is displayed by curing the layer with LED-UV at 385nm to form a pre-ceramic polymer, and then pyrolyzing the pre-ceramic polymer at 1000 ℃ in an inert atmosphere to form a pyrolyzed ceramic material. Fig. 2 shows a photograph of a pre-ceramic polymer (right side) and a darker pyrolyzed ceramic part (left side).

Fig. 3 is a graph of thermogravimetric analysis for pyrolyzing a UV-cured preceramic polymer into a pyrolyzed ceramic material, which measures the loss of sample mass over time as the pyrolysis temperature increases.

Example 3: production of a preceramic polymer composition comprising an acrylate-functionalized polycarbosilane.

Allylhydropolycarbosilane (77 g) was combined with acrylic acid (23 g) in a vessel to form a reaction mixture. The reaction mixture is stirred under argon at a reaction temperature of from 20 ℃ to 80 ℃ for a reaction time of from 1 hour to 48 hours (wherein the reaction temperature and the reaction time are inversely proportional). The result of the reaction is a UV reactive acrylate functionalized polycarbosilane preceramic polymer.

A polymerization initiator, such as benzophenone, may be added to the initial reaction mixture or the acrylate-functionalized polycarbosilane at a concentration of about 1 to 2 weight percent and stirred until dissolved or suspended.

A free radical inhibitor, such as hydroquinone, may be added to the initial reaction mixture or the acrylate-functionalized polycarbosilane at a concentration of about 0.001 wt% to 1wt% and stirred until dissolved or suspended.

A 3D printing resolution agent, such as 2- (2-hydroxyphenyl) -benzotriazole, may be added to the initial reaction mixture or the acrylate-functionalized polycarbosilane at a concentration of about 0.001 wt% to 1wt% and stirred until dissolved or suspended.

The UV-reactive acrylate-functionalized polycarbosilane preceramic polymer may be 3D printed (e.g., by stereolithography) and thermally treated (e.g., by pyrolysis) to form a 3D ceramic structure containing SiC (and possibly SiOC).

Example 4: production of a preceramic polymer composition comprising an acrylate-functionalized polycarbosilane.

Allylhydrocarbosilane (35 g) was combined with allylphenylhydrocarbosilane (35 g) and stirred to obtain a homogeneous initial mixture. The mixing temperature may be from about 20 ℃ to 80 ℃ for a mixing time of from about 1 minute to 4 hours. The initial mixture was combined with acrylic acid (30 grams) in a vessel to form a reaction mixture. The reaction mixture is stirred under argon at a reaction temperature of from 20 ℃ to 80 ℃ for a reaction time of from 1 hour to 48 hours (wherein the reaction temperature and the reaction time are inversely proportional). The result of the reaction is a UV reactive acrylate functionalized polycarbosilane preceramic polymer.

A polymerization initiator, such as 2, 2-dimethoxy-2-phenylacetophenone, may be added to the initial reaction mixture or the acrylate-functionalized polycarbosilane at a concentration of about 1 to 2 weight percent and stirred until dissolved or suspended.

A free radical inhibitor, such as methyl hydroquinone, may be added to the initial reaction mixture or the acrylate-functionalized polycarbosilane at a concentration of about 0.001 wt% to 1wt% and stirred until dissolved or suspended.

Example 5: production of a preceramic polymer composition comprising an acrylate-functionalized polycarbosilane.

Dry Tetrahydrofuran (THF) (300 g) was added to the vessel and purged with argon. Allylhydrocarbosilane (35 g) and allylphenylhydrocarbosilane (35 g) were combined in a vessel and stirred to obtain a homogeneous initial mixture in the vessel. The mixing temperature may be from about 20 ℃ to 75 ℃ for a mixing time of from about 1 minute to 4 hours. The initial mixture was combined with acrylic acid (30 grams) in a vessel (or transferred to a separate reactor) to form a reaction mixture. The reaction mixture was refluxed at 75 ℃ under argon for a reaction time from 1 to 24 hours (where the reaction temperature and reaction time are inversely proportional), with the vapors being condensed and returned to the reaction mixture. The result of the reflow reaction is a UV reactive acrylate functionalized polycarbosilane preceramic polymer that can be vacuum dried.

A polymerization initiator, such as camphorquinone, may be added to the initial reaction mixture or the acrylate-functionalized polycarbosilane at a concentration of about 1 to 2 weight percent and stirred until dissolved or suspended.

A free radical inhibitor, such as ethyl hydroquinone, may be added to the initial reaction mixture or the acrylate-functionalized polycarbosilane at a concentration of about 0.001 wt% to 1wt% and stirred until dissolved or suspended.

A 3D printing resolution agent, such as 2-hydroxyphenyl-benzophenone, may be added to the initial reaction mixture or the acrylate-functionalized polycarbosilane at a concentration of about 0.001 to 1 weight percent and stirred until dissolved or suspended.

Example 6: production of a preceramic polymer composition comprising an acrylate-functionalized polycarbosilane.

Allylhydropolycarbosilane (77 grams) was combined with acrylic acid (23 grams) and a crosslinking agent in a vessel to form a reaction mixture. The crosslinking agent divinyldimethylsilane (15 g) was added to the vessel and stirred until dissolved.

The reaction mixture is stirred under argon at a reaction temperature of from 20 ℃ to 80 ℃ for a reaction time of from 1 hour to 48 hours (wherein the reaction temperature and the reaction time are inversely proportional). The result of the reaction is a UV reactive acrylate functionalized polycarbosilane preceramic polymer.

A polymerization initiator, such as bis (2, 4, 6-trimethylbenzoyl) -phenylphosphine oxide, may be added to the initial reaction mixture or the acrylate-functionalized polycarbosilane at a concentration of about 1 to 2 weight percent and stirred until dissolved or suspended.

A free radical inhibitor, such as methoxyhydroquinone, may be added to the initial reaction mixture or the acrylate-functionalized polycarbosilane at a concentration of about 0.001 wt% to 1wt% and stirred until dissolved or suspended.

A 3D printing resolution agent (such as 2-hydroxyphenyl-s-triazine) may be added to the initial reaction mixture or the acrylate-functionalized polycarbosilane at a concentration of about 0.001 wt% to 1wt% and stirred until dissolved or suspended.

Example 7: production of a preceramic polymer composition comprising an acrylate functionalized polycarbosilane.

Allylhydropolycarbosilane (77 grams) and acrylic acid (23 grams) were combined in a vessel to form a reaction mixture. The crosslinking agent 1, 3-divinyl-1, 3-tetramethyldisilazane (15 grams) was added to the vessel and stirred to dissolve.

The reaction mixture is stirred under argon at a reaction temperature of from 20 ℃ to 80 ℃ for a reaction time of from 1 hour to 48 hours (wherein the reaction temperature and the reaction time are inversely proportional). The result of the reaction is a UV reactive acrylate functionalized polycarbosilane pre-ceramic polymer.

A polymerization initiator, such as benzophenone, may be added to the initial reaction mixture or the acrylate-functionalized carbonitride silane at a concentration of about 1 to 2 weight percent and stirred until dissolved or suspended.

A free radical inhibitor, such as hydroquinone, may be added to the initial reaction mixture or the acrylate-functionalized polycarbosilane at a concentration of about 0.001% to 1% by weight and stirred until dissolved or suspended.

A 3D printing resolution agent, such as 2- (2-hydroxyphenyl) -benzotriazole, may be added to the initial reaction mixture or the acrylate functionalized polycarbosilane at a concentration of about 0.001 wt% to 1wt% and stirred until dissolved or suspended.

The UV reactive acrylate functionalized polycarbosilane preceramic polymer may be 3D printed (e.g., by stereolithography) and thermally treated (e.g., by pyrolysis) to form a 3D ceramic structure containing SiCN (and possibly SiOCN).

Example 8: production of a preceramic polymer composition comprising an acrylate functionalized polycarbosilane.

Allylhydropolycarbosilane (77 grams) and acrylic acid (23 grams) were combined in a first vessel to form a first reaction mixture. The crosslinking agent divinyldimethylsilane (15 g) was added to the first vessel and stirred until dissolved.

The first reaction mixture is stirred under argon at a first vessel reaction temperature of from 20 ℃ to 80 ℃ for a first vessel reaction time of from 1 hour to 48 hours (wherein reaction temperature and reaction time are inversely proportional).

In the second vessel, the polycarbosilazane was stirred under argon. 2-isocyanatoethyl acrylate is added to the second vessel and the second mixture is stirred under argon. The second vessel reaction temperature may be from about 0 ℃ to 50 ℃ for a second vessel reaction time of from about 1 hour to 48 hours.

The contents of the second vessel were added to the first vessel and stirred until dissolved. Additional reaction time from about 1 to 24 hours may be provided at reaction temperatures that may be from about 0 to 80 ℃. The result of the reaction is a UV reactive acrylate functionalized polycarbosilane pre-ceramic polymer.

A polymerization initiator, such as benzophenone, may be added to the initial reaction mixture or the acrylate functionalized polycarbosilane at a concentration of about 1 to 2 weight percent and stirred until dissolved or suspended.

The UV-reactive acrylate-functionalized polycarbosilane preceramic polymer may be 3D printed (e.g., by stereolithography) and thermally treated (e.g., by pyrolysis) to form a 3D ceramic structure containing SiCN (and possibly SiOCN).

Example 9: 3D printed SiC was produced from an acrylate functionalized polycarbosilane.

The UV reactive acrylate functionalized polycarbosilane preceramic polymer of example 4 was 3D printed into plates and strips following the top down printing technique using a UV based digital light projection 3D printer Prodways L5000. The resin was filled into the barrel. The moving print platform was initially positioned about 50 microns of a single print layer thickness below the resin surface. The UV beam is selectively projected onto the resin via a scanning mirror. As the printing platform moves downward, the final 3D part is printed with a cross-sectional image layer by layer. Fig. 4 is a photograph of a 3D printed polymer plate and strip. Fig. 6 also shows a 3D printed polymer strip (image on left).

The 3D printed pre-ceramic polymer was then converted to an amorphous SiC ceramic material via pyrolysis at a temperature of 1000 ℃ for 1 hour under an atmosphere of argon gas. Fig. 5 is a photograph of amorphous SiC plates and strips. Fig. 6 also shows an amorphous ceramic strip (second image from left).

In one experiment, amorphous SiC ceramic materials were subjected to high temperature crystallization at a temperature of 1500 ℃ for 4 hours. In another experiment, amorphous SiC ceramic material was subjected to high temperature crystallization at a temperature of 1600 ℃ for 4 hours. Fig. 6 is a photograph of crystalline SiC stripes at 1500 ℃ (third image from left) and 1600 ℃ (image on right). It was observed that the 3D printed and pyrolyzed strips survived high temperature crystallization.

Thermogravimetric analysis of the pre-ceramic polymer when pyrolyzed up to 1000 ℃ and then further heat treated to 1500 ℃ is shown in fig. 7 and 8.

Fig. 9 shows the X-ray powder diffraction pattern of a ceramic material obtained by high temperature treatment at 1600 ℃ for 4 hours in argon. The X-ray powder diffraction pattern revealed the presence of the beta SiC phase in the crystalline ceramic material.

The versatility and application of these pre-ceramic resin formulations makes them particularly useful. Various applications in the automotive and aerospace industries may benefit from, among other things, the ability to 3D print high strength and high temperature ceramic structures that may be obtained from the disclosed formulations. These ceramic 3D parts or materials can be used in lightweight, high temperature structural applications or other applications that utilize unique microstructures such as, but not limited to, jet engine nozzles, nose cones, catalyst supports, engine components, and microelectromechanical systems and devices.

In this detailed description, reference has been made to a number of embodiments and to the accompanying drawings, in which specific exemplary embodiments of the invention are shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that modifications to the disclosed embodiments may be made by those skilled in the art.

Where methods and steps described above indicate certain events occurring in a certain order, those of ordinary skill in the art will recognize that the order of certain steps may be modified and that such modifications are in accordance with the variations of the present invention. In addition, certain steps may be performed concurrently in a parallel process, where possible, or may be performed sequentially.

All publications, patents, and patent applications cited in this specification are herein incorporated by reference in their entirety as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated herein by reference.

The above-described embodiments, variations and drawings are intended to provide an indication of the utility and versatility of the present invention. Other embodiments that do not provide all of the features and advantages set forth herein may also be utilized without departing from the spirit and scope of the present invention. Such modifications and variations are considered to be within the scope of the invention as defined by the claims.

Claims

1. A pre-ceramic resin formulation for 3D printing and radical or cationic polymerization, the pre-ceramic resin formulation comprising:

(a) A functionalized carbosilane having the following chemical structure:

wherein:

R ¹ selected from the group consisting of: hydrogen, vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinylAmide groups, vinyltriazine groups, vinyl isocyanurate groups, acrylate groups, methacrylate groups, alkylacrylate groups, phenyl groups, halogen groups, thiol groups, alkylthiol groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, mercaptopropionate groups, mercaptoacetate groups, aromatic groups, and combinations thereof;

R ² selected from the group consisting of: vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, methacrylate groups, alkylacrylate alkyl ester groups, phenyl groups, halogen groups, thiol groups, alkylthiol groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, mercaptopropionate groups, thioglycolate groups, aromatic groups, and combinations thereof; and is

n =1 to 100;

(b) A photoinitiator;

(c) Optionally, a free radical inhibitor; and

(d) Optionally, 3D printing a resolution agent.

2. The pre-ceramic resin formulation of claim 1, wherein R ¹ Or R ² Is a vinyl group or an allyl group.

3. The pre-ceramic resin formulation of claim 1, wherein R ¹ Or R ² Is an acrylate group or a methacrylate group.

4. The pre-ceramic resin formulation of claim 1,wherein R is ¹ Or R ² Is a thiol group or a thiol-containing group.

5. The pre-ceramic resin formulation of claim 1, wherein the pre-ceramic resin formulation contains at least two different functionalized carbosilanes, each conforming to the chemical structure, wherein R ¹ 、R ² And n is independently selected for the different functionalized carbosilanes.

6. The pre-ceramic resin formulation of claim 1, wherein the photoinitiator is present in the pre-ceramic monomer formulation at a concentration of from about 0.001 wt% to about 10 wt%.

7. The pre-ceramic resin formulation of claim 1, wherein the free radical inhibitor is present in the pre-ceramic monomer formulation at a concentration of from about 0.001 wt% to about 10 wt%.

8. The pre-ceramic resin formulation of claim 1, wherein the 3D printing resolution agent is present in the pre-ceramic resin formulation at a concentration of from about 0.001 wt% to about 10 wt%.

9. The pre-ceramic resin formulation of claim 1, wherein the pre-ceramic monomer formulation further comprises a thermal radical initiator.

10. The pre-ceramic resin formulation of claim 1, wherein the pre-ceramic resin formulation further contains a cross-linking agent.

11. The pre-ceramic resin formulation of claim 1, wherein the pre-ceramic monomer formulation further comprises from about 0.1 vol% to about 70 vol% of a solid phase filler.

12. A preceramic polymer composition comprising a functionalized polycarbosilane having the following polymer structure:

wherein:

R ² selected from the group consisting of: vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, alkylacrylate groups, phenyl groups, halogen groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, and combinations thereof; and is provided with

n =2 to 200.

13. The preceramic polymer composition of claim 12, wherein the preceramic polymer composition comprises at least two different functionalized polycarbosilanes, each conforming to the polymer structure, wherein R ¹ 、R ² And n is independently selected for said different functionalisationsA polycarbosilane.

14. The preceramic polymer composition of claim 12, wherein the preceramic polymer composition comprises a functionalized polycarbosilane copolymer having the following copolymer structure:

wherein:

R ¹ 、R ² 、R ³ and R ⁴ Independently selected from the group consisting of: hydrogen, vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, alkylacrylate groups, phenyl groups, halogen groups, thiol groups, alkylthiol groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, mercaptopropionate groups, thioglycolate groups, aromatic groups, and combinations thereof;

R ³ and R ⁴ Is different from R ¹ Or R ² ；

n =1 to 200; and is provided with

m =1 to 200.

15. The preceramic polymer composition of claim 14, wherein the copolymer structure is:

wherein R is ¹ Is hydrogen, R ² Is an allyl radical, R ³ Is hydrogen, and R ⁴ Is a vinyl group.

16. The preceramic polymer composition of claim 14, wherein the copolymer structure is:

wherein R is ¹ Is hydrogen, R ² Is an allyl radical, R ³ Is an acrylate group, and R ⁴ Is hydrogen.

17. The preceramic polymer composition of claim 14, wherein the copolymer structure is:

wherein R is ³ Is selected from C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups.

18. The preceramic polymer composition of claim 14, wherein the copolymer structure is:

19. The preceramic polymer composition of claim 14, wherein the copolymer structure is:

20. The pre-ceramic polymer composition of claim 12, wherein the pre-ceramic polymer composition further comprises a cross-linking agent.

21. The preceramic polymer composition of claim 12, wherein the preceramic polymer composition comprises a copolymer repeat unit that is different from a repeat unit contained in the functionalized polycarbosilane.

22. The preceramic polymer composition of claim 21, wherein the copolymer repeating units are polycarboxysilane repeating units containing nitrogen bonded to silicon and/or carbon.

23. The pre-ceramic polymer composition of claim 22, wherein the nitrogen is bonded to a functional group selected from the group consisting of: hydrogen, vinyl group, allyl group, ethynyl group, C ₁ -C ₁₈ Unsubstituted or substituted alkyl groups, ester groups, amine groups, hydroxyl groups, vinyl ether groups, vinyl ester groups, glycidyl ether groups, vinyl amide groups, vinyl triazine groups, vinyl isocyanurate groups, acrylate groups, methacrylate groups, alkyl acrylate groups, phenyl groups, halogen groups, thiol groups, alkyl thiol groups, thiol-containing groups, cyano groups, cyanate groups, thiocyanate groups, mercaptopropionate groups, thioglycolate groups, aromatic groups, and combinations thereof.

24. The pre-ceramic polymer composition of claim 12, wherein the pre-ceramic polymer composition further comprises from about 0.1% to about 70% by volume of a solid phase filler.

25. The pre-ceramic polymer composition of claim 12, wherein the pre-ceramic polymer composition is in the form of a 3D printed polymer.