3D Printing Thermally Stable High‐Performance Polymers Based on a Dual Curing Mechanism

High‐performance polymers are an important class of materials that are used in challenging conditions, such as in aerospace applications. Until now, 3D printing based on stereolithography processes can not be performed due to a lack of suitable materials. There is report on new materials and printing compositions that enable 3D printing of objects having extremely high thermal resistance, with Tg of 283 °C and excellent mechanical properties. The printing is performed by a low‐cost Digital Light Processing printer, and the formulation is based on a dual‐cure mechanism, photo, and thermal process. The main components are a molecule that has both epoxy and acrylate groups, alkylated melamine that enables a high degree of crosslinking, and a soluble precursor of silica. The resulting objects are made of hybrid materials, in which the silicon is present in the polymeric backbone and partly as silica enforcement particles.


Introduction
High-performance polymers (HPPs) are a group of polymeric materials that retain their mechanical, thermal, and chemical properties when subjected to harsh environmental conditions such as high temperature, high pressure, and corrosive chemicals. Among these polymers, the most common are (PEEK), cyanate esters (CA), and polyetherimide (PEI). HPPs are used in a wide variety of industries, including aerospace, construction, automotive, electronics, and defense. However, they are consumed in low-volume applications due to their high cost. [1] Until 2018, the epoxy resin family led the high-performance resin market. The resins are common, easy to produce from synthetic and bio-based epoxides, and significantly cheaper than HPPs such as PEI and PEEK. [2] Moreover, epoxy resins This hybrid is polymerized in the presence of radical and cationic photoinitiators in two steps: i) photopolymerization of the acrylates and partial polymerization of the epoxide and ii) post-curing of the epoxides by heating. [12] It was reported that increasing the ratio between the epoxy and the acrylates reduces the shrinkage and improves the mechanical properties. [13] Epoxy-acrylate hybrid systems have been previously molded, [14,15] and printed by Digital Light Processing (DLP). [16][17][18][19][20][21][22][23][24][25] In both methods, the resulting hybrid polymers usually have inferior mechanical properties compared to the epoxy resin without the acrylate component. The reported Young's modulus of the hybrid polymers is 0.036-2.59 GPa, with a maximum Tg of only 150 °C (Table S1, Supporting Information).
Another approach that may be suitable for making epoxyacrylate hybrid resin is combining both acrylate and epoxide in the same molecule. This approach was used by Chattopadhyay et al. for 2D coating, while the standard epoxy DGEBA was converted into the dual cure oligomer Bisphenol A epoxidemonoacrylate (BAEMA, Figure 1). [26] BAEMA was also used as an additive to DGEBA for thin film formation. [27] The Tg of BAEMA homopolymer is higher than that of commercial DGEBA (118 and 77-98 °C (depending on the manufacturer), respectively), but this value is too low for meeting HPPs standards. [28] To the best of our knowledge, currently, there are no epoxybased, photopolymerizable resins that can be 3D printed by conventional stereolithography printers, which would result in 3D structures having high heat resistance and good mechanical properties, as is required for HPP-based applications.
Here we present new epoxy-based materials for 3D printing HPPs, based on a dual curing mechanism. The new printing compositions are composed of a dual-cure epoxy oligomer BAEMA with an alkylated melamine, which enables 3D printing of structures with a Tg of 241 °C and excellent mechanical properties. Further addition of a sol-gel precursor containing photocurable groups enables the in situ formation of SiO 2 particles, resulting in a polymer with superior thermal stability (Tg = 283 °C) and Young's modulus of 2.85 GPa. These compositions enable the fabrication of heat-stable 3D objects by low-cost DLP printers at high resolution.

Results and Discussion
At first, the dual cure epoxy oligomer was synthesized, followed by polymerizing the oligomer with alkylated melamine and sol-gel precursor.

Homopolymerization of BAEMA
The resin synthesis, BAEMA, was performed by reacting DGEBA with acrylic acid, according to a previous report (Figure 1(i)). [28] Based on nuclear magnetic resonance (NMR) measurements ( Figure S1, Supporting Information), epoxide to acrylate conversion was 53%. BAEMA (indicated as blue throughout the manuscript figures) was homopolymerized in two steps: radical photopolymerization of the acrylates Adv. Funct. Mater. 2023, 33, 2214368 Figure 1. DLP using dual-cure epoxy enables complex structure objects with stereolithography resolution. i) The synthesis of DGEBA with the acrylate group results in BAEMA with two functional groups: epoxy and acrylate. ii) Light irradiation initiates partial photopolymerization of the acrylic groups to form a thermoset on-demand, fixating and forming green-body ("as-printed" objects before heat curing). iii) Thermal curing polymerizes the epoxy groups and fully converts the acrylates, resulting in a fully crosslinked cured object. and cationic photopolymerization of the epoxide groups ( Figure 1(ii)), followed by thermal curing (Figure 1(iii)), as described in the experimental section. FTIR spectroscopy of the dual-cured BAEMA indicated full polymerization by the disappearance of the characteristic peaks of the acrylate and epoxide groups at 1406 and 914 cm −1 , respectively ( Figure S2, Supporting Information). It should be noted that the final BAEMA oligomer includes residues of unreacted acrylic acid, which functioned later on as an acid catalyst for the epoxy polymerization.
The Tg value of the homopolymer was measured for casted samples that were assessed by three-point bending dynamic mechanical analysis (DMA). Figure 2b of the dual-cured BAEMA depicts a Tg of 134 °C indicated by the maximum of the tan δ curve. This value is higher than the reported one (118 °C), probably due to a higher crosslinking degree. [28] Moreover, quasi-static tensile measurements of dog bones revealed Young's modulus and UTS of 1772 and 20.1 MPa, respectively.
The effect of the thermal curing step could be seen when looking at the microstructure of the homopolymer using Scanning Electron Microscopy (SEM). While SEM revealed a smooth surface for both photocuring and thermal curing steps, fractures cross-section for that photocuring resulted in a brittle fracture surface. A typical topology of a brittle epoxy resin, characterized by distinct fracture lines, can be seen for thermal curing ( Figure S3, Supporting Information).

Alkylated Melamine as a Hardener for BAEMA
Alkylated melamine-formaldehyde resins, such as methylated and butylated melamine, are commercial materials that have several applications, such as in coatings and finishing of automobiles, [29] and floor covering. [30] When heated in the presence of an alcohol, a transesterification reaction takes place, whereas the reaction with epoxide leads to the formation of a highly crosslinked system with five and six-membered rings ( Figures S4 and S5, Supporting Information). [31] Therefore, alkylated melamine (Cymel) was used as a hardener for the above dual-cure epoxy BAEMA oligomer (BAEMA: Cymel samples are shown in green throughout the manuscript figures).
The printing composition was prepared by simple mixing of BAEMA resin, Cymel, and the photoinitiator diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide (TPO) (at 49:49:2 wt.%). The resulting solutions were cured in a mold by UV irradiation followed by thermal curing. The photocuring and thermal reactions were followed by FTIR spectroscopy, indicating the photopolymerization of the acrylate groups (intensity reduction of the band at 1406 cm −1 ) and the reaction between the epoxide and Cymel after heat curing (disappearance of the epoxide absorptions peak at 914 cm −1 and reducing the NH band of the curing agent at 1495 cm −1 ( Figure S6, Supporting Information)). Furthermore, it was found that upon irradiation for 30 s, the conversion of acrylate bonds was partial, and upon heating for 1 h at 100 °C followed by 4 h at 275 °C, full conversion of acrylates and epoxide occurred (based on FTIR measurements, Figure S6, Supporting Information). It should be noted that thermal curing at 240 and 275 °C resulted in the formation of objects with light brown or dark brown colors, respectively.
When looking at BAEMA: Cymel dual-cured fractured sample using SEM, two morphologies, smooth and tortuous, can be seen on the surface ( Figure S7 Figure S8, Supporting Information). c) various screws, and d) a highly complex diamond structure were printed. area with good miscibility of Cymel with BAEMA resin. The tortuous domains are rough and are expected to resist deformation and crack propagation due to the crosslinking density. [32] The cross-section (right side) is characterized by fracture lines indicating the high impact resistance of the polymer. [33] To optimize the epoxy-to-Cymel ratio, compositions with weight ratios of 1:1, 2:1, 3.2:1 were studied by determining the Tg values. As presented in Figure 2a, the 1:1 ratio results in the best composition, with a Tg of 241 °C. Therefore, according to these results, the following printing experiments were performed with compositions having the 1:1 (wt.%) ratio. Moreover, the Tg was validated by differential scanning calorimetry (DSC). 1:1 (wt.%) ratio photocured sample was heated to 350 °C at 10 °C min −1 , and a Tg of 250 °C was observed ( Figure S9, Supporting Information).
The next step was to evaluate if the curing temperature would affect the Tg. Therefore, following the photocuring of samples prepared in molds, they were thermally cured up to the high temperature of 275 °C. Figure 2b shows the tan δ as a function of temperature during the DMA measurement for two thermal curing temperatures, 275 and 240 °C. It appears that the Tg of the pure BAEMA homopolymer cured at 275 °C, is characterized by only one peak at 134 °C. In contrast, two peaks were detected in the polymers containing the hardener. These results indicate the formation of two phases in the polymeric matrix, in agreement with the SEM image ( Figure S7, Supporting Information). Most importantly, it was found that increasing the curing temperature from 240 to 275 °C led to a very significant increase of the Tg, from 187 up to 241 °C, probably due to a higher degree of crosslinking.
The heat deflection temperature (HDT) of BAEMA: Cymel sample that was thermally cured at 275 °C was 179 °C at 0.45 MPa.
Standard dog bone samples were printed to evaluate the quasi-static mechanical properties of BAEMA: Cymel polymer after curing at 240 and 275 °C by tensile measurement ( Figure S10, Supporting Information). It was found that the UTS of the homopolymer cured at 275 °C was only 20.1 MPa, with Young's modulus of 1772 Mpa, whereas BAEMA: Cymel polymer cured under the same conditions had almost a doubled strength, with UTS of 37.5 Mpa and Young's modulus of 2432 Mpa. The improvement of the mechanical properties of the polymer is attributed to the high crosslinking degree enabled by the alkylated melamine.
Comparing these results to those previously reported for blending acrylates and epoxides (Table S1, Supporting Information) indicates that in some cases, a higher Young's modulus and tensile strength can be achieved, [15,19,21,25] however, their Tg values are below 150 °C. Moreover, the flexural modulus evaluated by three-point bending measurements was 3.3 GPa which is in the same order of magnitude as other reported materials ( Figure S11, Supporting Information).
In the next step, 3D objects composed of BAEMA: Cymel 1:1 (wt.%) were printed by a commercial low-cost DLP printer. Complex models such as various screws ( Figure 2c) and a diamond (Figure 2d) are shown before thermal curing, a stage that is known as "green-body".

Improving Tg by a Silica Sol-Gel Precursor
A common method to harden polymers is based on the addition of solid fillers such as metal oxide particles (SiO 2 , TiO 2 , ZrO 2, and Al 2 O 3 ). Adding such particles to DLP printing compositions will present challenges in the form of light scattering, agglomeration of particles, and sedimentation. To avoid this, we present a new approach to further improve the mechanical properties of the above epoxy polymers based on adding solgel silica precursors to the resin. Sol-gel precursors undergo hydrolysis while heated in the presence of an acid catalyst to form silanol groups (SiOH). The silanol groups can react with a hydroxyl of epoxide group of BAEMA oligomer, thus providing an additional crosslinking of the epoxy polymer. [34] In addition, the silanol may also react with another silanol group via a condensation process with the formation of SiOSi bonds, leading to the in situ formation of silica particles.
Compared to nanoparticle dispersion, the advantages of in situ SiO 2 formation from a soluble precursor are avoiding stability problems and high viscosity, which often occurs by dispersing particles in liquids. [35] Furthermore, the sol-gel precursor can also function as a reactive diluent, adding a unique cross-linking mode. Such an approach was reported for hardening DGEBA resin by 3-glycidyloxypropyltrimethoxysilane, [36,37] tetraethoxysilane, [38] as well as titanium and zirconium precursors, [39] and the formation of organic-inorganic hybrid material.
This work uses acryloxymethyl trimethoxysilane (AMTMS) as a dual-function sol-gel precursor. AMTMS is a unique material containing an acrylate group that can photopolymerize during printing, similar to the precursors we used previously for the 3D printing of ceramics. [40][41][42][43][44] Afterward, during the thermal curing, this molecule can react with epoxides, hydroxyls, and silanols groups bonded to the resin (Figure 3a). Finally, water was added at a low concentration to the formulation to enable an efficient sol-gel process. Thus, a typical composition is composed of BAEMA: Cymel: AMTMS: TPO: H 2 O, a ratio of 1:1:0.05:0.02:0.02 (wt.%).
Various techniques characterized the obtained polymer. SEM of printed samples after thermal curing showed, as previously in samples without the sol-gel precursor, two types of structures, smooth and tortuous (Figure 3b). In addition, the presence of silicon oxide within the polymer was detected by EDX, having particles in size range of a few to tens of microns ( Figure 3c).
X-Ray Photoelectron Spectroscopy (XPS) used to characterize the surface layer down to about 10 nm depth revealed that the polymer contains carbon (78.35%), nitrogen (5.38%), oxygen (13.21%), and silicon (3.06% atomic percent). Figure 3d presents the commonly used fitting of the Si 2p spectrum. [45] The peak of the raw data (black line) matches very well with two components: The first one corresponds to alkoxy/ alkyl silane bonds at 102.5 and 103.1 eV (red lines, spin 3/2, and spin ½, respectively), indicating the formation of SiOC bond between AMTMS and the epoxy network. The second component is SiO 2, based on peaks at 103.3 and 103.9 eV (olive lines, spin 3/2 and 1/2, respectively). According to the results, 15% of the silicon precursor was converted to SiO 2 , and 85% was chemically bonded to the epoxy framework.
Next, DMA measurement evaluated the effect of the curing temperature on the Tg. Young's moduli obtained from a quasi-static tensile measurement of printed dog bones are shown in Figure 3f. The Young's modulus of samples cured at 240 °C was found to be 2420 MPa, 30% higher than that of the homopolymer and 10% higher than for the ink without AMTMS ( Figure S8, Supporting Information). When the samples were heated between 240 to 260 °C, Young's modulus did not change, but at 275 °C, it increased to 2850 MPa. This high modulus results from the presence of silicon precursor, which has a dual effect: further cross-linking the polymer and formation of bound SiO 2 particles as a filler. Moreover, a flexural modulus value of 3.3 GPa was obtained ( Figure S15, Supporting Information). Figure 3g presents four models of printed screws to show the printability of the new formulations containing BAEMA: Cymel: AMTMS. The objects were cured at different temperatures. The first screw (left) was only photocured, while the three others were also thermally cured at 180, 240, and 275 °C, respectively. As shown, the light yellowish color of the objects gradually turned dark brown with the increase in curing temperatures. In addition to the change in color, the 3D object shrank gradually  Figure S12, Supporting Information). b) SEM image of photothermal cured polymer interface at two types of structures; c) SEM image of SiO 2 particles in the polymer. d) XPS results indicate the presence of SiO 2 particles and alkoxy/alkyl silane covalently bound to the epoxy network. e) DMA measurements of two thermal curing temperatures revealed that for thermal curing of 275 °C Tg increases to 283 °C (storage and loss modulus can be seen in Figure S13, Supporting Information). f) Young's modulus of printed dog bones cured at 240, 250, 260 and 275 °C (all stress-strain raw data can be seen in Figure S14, Supporting Information). g) Printed screws: before thermal curing (left) and after curing at 180, 240 and 275 °C (left to right). and isotropically in XY and Z axis with increasing temperature. Green-body dimension was 8% smaller than the designed one, while samples after thermal cure of 275 °C resulted in 19% shrinkage (Figure S16, Supporting Information). As common in this field, proper selection of photo absorbers can maximize and increase the obtained resolution even more. [46]

How Unique are these 3D-Printing Compositions?
The heat stability of the polymers was evaluated by thermogravimetric analysis (TGA). It was found that for a given weight loss of 3% w/w, the BAEMA: Cymel was stable up to 321 °C, and BAEMA: Cymel: AMTMS was stable till 298 °C ( Figure S17, Supporting Information). Figure 4 compares the literature values of the Tg's at various Young's moduli for reported hybrid polymers made of blended acrylates and epoxides monomers with the materials developed in this work (details presented in Tables S1 and S2, Supporting Information). It is clearly seen that all the reported hybrid polymers have a Tg lower than 150 °C, and in most cases, Young's moduli are below 2.5 GPa (black circles).
In comparison, the dual-cured oligomer formed by combining both acrylate and epoxide in the same molecule (BAEMA homopolymer, blue circle), did not significantly improve the polymer's thermal stability. However, the BAEMA dual-cured oligomer with Cymel as a hardener enabled forming of polymeric objects with an excellent Tg value of 241 °C and a high Young's modulus (green square). Therefore, it could be expected that replacing the epoxide group with an acrylate group in the BAEMA oligomer will cause a deterioration of mechanical properties. Nevertheless, the rigidity and highly crosslinked structure enabled by the alkylated melamine hardener compensate for the acrylates' negative effect. The addition of AMTMS, which led to a significant increase of Tg to 283 °C, also resulted in an outstanding Young's modulus of 2.85 GPa (purple square), due to the unique crosslinking and presence of silica particles.

Conclusion
This research focuses on developing new epoxy-based 3D printing compositions that result in high-performance objects, extremely high thermal stability, and excellent mechanical properties. The new materials are printed by stereolithographybased technologies, as presented by commercially available DLP printers. Unlike the common approach of blending epoxy and acrylate monomers to enable both photopolymerization and thermal curing, here we present the formation and application of a bifunctional oligomer, having both acrylate and epoxy groups within the same molecule. This oligomer is combined with unique multifunctional hardeners, alkylated melamine (Cymel), and silica precursor (AMTMS). The fabrication process is composed of DLP printing, thus forming the required object by photopolymerization of the oligomer, followed by heat curing the epoxides with Cymel. This specific hardener led to the formation of a highly crosslinked, high-performance polymer characterized by superior properties: excellent Tg (241 °C) with Young's modulus of 2.43 GPa and UTS value of 37.5 MPa.
Further addition of the sol-gel dual precursor AMTMS provided a unique multifunction: photopolymerization, crosslinking, and forming silica particles. The combination of all three led to the extremely high Tg value of 283 °C, excellent Young's modulus of 2.85 GPa, and UTS value of 44.25 MPa.
We expect that the new printing compositions will open the way to the fabrication of 3D objects composed of HPPs by a simple process that does not require special costly printers such as FDM that can only operate at very high temperatures.
Synthesis of Dual Cure Oligomer BAEMA: The dual-cured oligomer BAEMA was synthesized according to a previous report by reacting DGEBA with 0.5 eq acrylic acid. [28] Briefly, DGEBA (100 gr, 82% purity, 0.24 mol) in 3 necked round flask was heated to 100 °C (bath temperature), under mechanical stirring at 200 rpm. Triphenylphosphine (226 mg, 0.86 mmol) and hydroquinone (72 mg, 0.65 mmol) were dissolved in acrylic acid (18.75 gr, 0.24 mol). The solution was added dropwise to the epoxy, and the reaction proceeded at 100 °C for 2 h Figure 4. Comparison of Young's modulus and Tg values of reported epoxy-acrylate polymers. Black circles correspond to reported hybrid polymers, blue circle corresponds to BAEMA dual cure homopolymer, black X symbol corresponds to commercial photocurable inks, green square corresponds to BAEMA: Cymel dual-cure polymer, purple squares correspond to BAEMA: Cymel: AMTMS dual-cure polymer (full details of the literature values are in Tables S1 and S2, Supporting Information). followed by 2 h at 120 °C. The resulting brown liquid turned viscous upon cooling.
The amount of unreacted acrylic acid in the oligomer was determined by proton NMR as follows: BAEMA (3.00 g) and D 2 O (2.00 g) were stirred at 60 °C for 2 h. The water phase was separated, and acetonitrile (5 mg) as an internal standard was added to 400 mg of the water solution. The acrylic acid residue was calculated from the NMR measurement based on the internal standard. In a typical synthesis, BAEMA included 0.023 (w/w) unreacted acrylic acid. The oligomer was used without further purification, using this acid as an internal catalyst for the epoxy polymerization and sol-gel process.
Ink Preparation: Ink compositions for molded samples were made as follows: BAEMA ink was prepared by mixing 6.5 g BAEMA and 3.2 g methyl ethyl ketone (MEK) at 55 ○ C to form a clear solution. Then, 0.13 g TPO was dissolved in the solution and mixed for 2 min, following 2 min of defoaming using a planetary mixer (AR-100, THINKY Co., Ltd., Japan) which resulted in a transparent homogenous formulation. BAEMA:Cymel ink was prepared by mixing 4.8 g BAEMA and 4.8 g Cymel NF 2000A at 55 °C to form a clear solution. Then, 0.2 g TPO was dissolved in the solution and mixed for 2 min, following 2 min of defoaming using a planetary mixer, resulting in a transparent homogenous formulation. BAEMA:Cymel:AMTMS ink was prepared by mixing 5.0 g BAEMA, 5.0 g Cymel NF 2000A, and 0.25 g AMTMS at 55 °C to form a clear solution. Then, 0.1 g TPO was dissolved in the solution, and water (0.1 g) was added. Finally, the ink was mixed for 2 min, following 2 min of defoaming using a planetary mixer, resulting in a transparent homogenous formulation.
Ink compositions for DLP printing samples were made as same as for the mold compositions with the addition of hydroquinone and sulforhodamine B sodium salt. For BAEMA and BAEMA:Cymel inks, 0.004% (w/w based on BAEMA hydroquinone) and 0.0005% (w/w based on BAEMA) sulforhodamine B sodium salt were added. For BAEMA:Cymel:AMTMS ink, 0.007% (w/w based on BAEMA hydroquinone), and 0.0005% (w/w based on BAEMA) sulforhodamine B sodium salt were added.
Nuclear Magnetic Resonance: BAEMA was characterized by proton NMR spectra (Bruker, Advance II 500 MHz, CDCl 3 ). The conversion of the epoxide group to acrylate was determined based on the integration ratio of peaks (δ 1.63, 3.34 ppm ) of the starting material and the product, according to Syu et al. [28] The number of the repeated units, n, was calculated based on integrating the two methyl groups' peaks (δ 1.63 ppm ). In a typical synthesis, epoxide to acrylate conversion was 53% and n = 2.3.
Fourier-Transform Infrared: For FTIR spectroscopy, neat samples were tested. The spectrometer (IRAffinity-1S, Shimadzu) was used at a resolution of 2 cm −1, and 20 scans were averaged for each spectrum. A transmittance mode was performed from 3600 to 500 cm −1 .
DLP Printing: 3D printing was performed using a DLP 3D printer (Pico 2, Asiga, Australia), equipped with a light source of 385 nm (light intensity of 18.23 mW cm −1 ). 3D-objects STL files were sliced to 0.05 µm thickness, the burn-in exposure time was set to 10 s, and the exposure time of other layers was set to 3 s a layer. The vat temperature was set to 36 °C.
After 3D printing, BAEMA printed objects were dipped for a few seconds in MEK and isopropanol to wash out ink excess, and then were kept overnight at room temperature for solvents evaporation, then heated for 1 h at 100 °C followed by heating 4 h at 275 °C with a heating rate of 10 °C min −1 . Both BAEMA: Cymel and BAEMA: Cymel: AMTMS 3D-printed objects were rinsed with a solution of 10% Cymel NF 2000A in CH 2 Cl 2 to remove the ink excess after 3D printing. The solvent was evaporated at room temperature overnight, then heated at 70 °C under vacuum for 1 h. After cooling, the objects were heated in an oven for 1 h at 100 °C followed by heating 4 h at 275 °C.
All screws 3D-objects STL files were obtained from McMASTER-CARR Quasi-Static Measurement: 30 ×10×1 mm (length x width x thickness) printed dogbones objects for the evaluation of mechanical properties were printed using inks detailed in the synthesis section. BAEMA postprinting included dipping in MEK and isopropanol for a few seconds and then kept overnight at room temperature for solvent evaporation. Postprinting of BAEMA:Cymel, and BAEMA:Cymel:AMTMS printed dogbones objects included rinsing with a solution of 10% Cymel NF 2000A in CH 2 Cl 2 to remove the ink excess, and the solvent was evaporated at room temperature overnight. All objects were cured in an oven for 1 h at 100 °C followed by additional thermal curing explicitly indicated in the text (240, 250, 260, or 275 °C) for 4 h, with a heating rate of 10 °C min −1 .
Tensile mechanical tests of the printed dog bones objects were performed on the fully cured samples using an Instron universal testing machine (Model 4500, Instron Corp., Norwood, MA) equipped with a 500 N load cell and operated at 10 mm min −1 .
Three-point bending tests were measured using DMA (Q800, TA Instruments), equipped with a 3-point bending mode with a sample holder of 10 mm span. The flexural test was carried out at 25 °C using 100 µm min −1 crosshead speed.
Dynamic Mechanical Analysis: Rectangular objects with a nominal sample size of 20 × 3 × 1 mm (length × width × thickness) were molded to evaluate DMA properties using inks detailed in the synthesis section. DMA (Q800, TA Instruments) was used to characterize the mechanical and thermomechanical properties of the materials tested using a 10 mm wide three-point bending grip. All measurements were performed using a three-point bending clamp in a nitrogen environment under a controlled strain mode at 1 Hz. The measurements were performed using a support span of 10 mm, a preload of 0.010 N, a temperature ramp rate of 5 °C min −1 , and a temperature range of 30-350 °C.
Heat Deflection Temperature: HDT measurements were conducted on a dynamical mechanical analyzer (Q800, TA Instruments) according to ASTM International Standard D 648. The rectangular molded objects with a nominal sample size of 20 × 3 × 1 mm (length × width × thickness) were analyzed using a 10 mm wide three-point bending grip under loading stress of 0.45 MPa, and a heating rate of 2 °C min −1 .
Thermal Properties: Thermogravimetric analysis was used to investigate the thermal stability of the samples. The TGA and DSC measurements of photothermal cured samples were performed using a Jupiter STA 449F3 thermogravimetric analyzer (Netzsch, Selb, Germany) at a scanning rate of 10 °C min −1 under a nitrogen atmosphere in the temperature range 25-350 °C.
Scanning Electron Microscopy: Mold samples for SEM were obtained after Irridium coating (Quorum 150 VS Plus). The samples were characterized by Magellan 400L instrument (FEI, USA), with Energy Dispersive Spectroscopy (EDS) Ultim Max.
X-Ray Photoelectron Spectroscopy: Measurements were performed using Kratos AXIS Supra spectrometer (Kratos Analytical Ltd., Manchester, U.K.) with Al Kα monochromatic radiation X-ray source (1486.6 eV). The XPS spectra were acquired with a takeoff angle of 90° (normal to analyzer); the vacuum condition in the chamber was 2 × 10 −9 Torr. The survey spectra were measured with pass energy 160 and 1 eV step size and high-resolution XPS spectra with a pass energy of 20 and 0.1 eV step size. The binding energies were calibrated using C 1 s peak energy as 285.0 eV. Data were collected and analyzed using ESCApe processing program (Kratos Analytical Ltd.) and Casa XPS (Casa Software Ltd.).

Supporting Information
Supporting Information is available from the Wiley Online Library or from the author.