PHOTOCURABLE POLYMER COMPOSITIONS

Abstract

The present invention relates to relates to a polymer formulation for three-dimensionally (3D) printing an article by stereolithography, the formulation comprising a functionalized polymer. The invention further relates to lithographic methods to form 3D objects that incorporate the aforementioned polymer formulation.

Claims

1. A polymer formulation (F) comprising, based on the total weight of the formulation (F): from 1 to 50 wt. %, based on the total weight of F, of at least one poly(aryl ethersulfone) (PAES) polymer (P) comprising at least one terminal group of formula (M1) or (M2): ##STR00023## wherein R.sup.2 is H or CH.sub.3, X is a bond or (CH.sub.2).sub.n with n ranging from 1 to 20, and wherein the number average molecular weight (Mn) of the polymer (P) is of more than 12,000 g/mol, as determined by gel permeation chromatography (GPC) using methylene chloride as a mobile phase and polystyrene standards, at least one polyfunctional acrylate, at least one solvent, optionally at least one photoinitiator, and optionally at least one blocker.

2. The formulation (F) of claim 1, wherein P is a PAES comprising recurring units (R.sub.PAES) of formula (L): ##STR00024## each R.sup.1 is, independently for each aromatic cycle, selected from the group consisting of a halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, alkali or alkaline earth metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal phosphonate, alkyl phosphonate, amine and quaternary ammonium; each i is, independently for each aromatic cycle, zero or an integer from 1 to 4; T is selected from the group consisting of a bond, —CH.sub.2—; —O—; —SO.sub.2—; —S—; C(O)—; —C(CH.sub.3).sub.2—; —C(CF.sub.3).sub.2—; —C(═CCl.sub.2)—; —C(CH.sub.3)(CH.sub.2CH.sub.2COOH)—; —N═N—; R.sub.aC═CR.sub.b—, where each R.sub.a and R.sub.b, independently from each other, is a hydrogen, a C1-C12-alkyl group, a C1-C12-alkoxy group, a C6-C18-aryl group; —(CH.sub.2).sub.m— and (CF.sub.2).sub.m— with m being an integer from 1 to 6; an aliphatic divalent group, linear or branched, of up to 6 carbon atoms; or a combination thereof.

3. The formulation (F) of claim 2, wherein T is selected from the group consisting of a bond, —SO.sub.2— and —C(CH.sub.3).sub.2—.

4. The formulation (F) of claim 2, wherein the PAES polymer comprises at least 50 mol. % (based on the total number of moles in the polymer) of recurring units of formula (L).

5. The formulation (F) of claim 2, wherein the PAES polymer comprises at least 50 mol. % (based on the total number of moles in the polymer) of recurring units selected from the group consisting of formulas: ##STR00025## ##STR00026## wherein R.sup.1 is independently for each aromatic cycle, selected from the group consisting of a halogen, alkyl, alkenyl, alkynyl, aryl, ether, thioether, carboxylic acid, ester, amide, imide, alkali or alkaline earth metal sulfonate, alkyl sulfonate, alkali or alkaline earth metal phosphonate, alkyl phosphonate, amine and quaternary ammonium and i is independently for each aromatic cycle, zero or an integer from 1 to 4.

6. The formulation (F) of claim 1, comprising at least 0.05 wt. % of polyfunctional acrylate, based on the total weight of the formulation (F).

7. The formulation (F) of claim 1, wherein the polyfunctional acrylate is according to formula (I): ##STR00027## wherein R.sup.3 is H or an alkyl having 1 to 5 carbon atoms, R.sup.4 is according to formula (II): ##STR00028## where n varies between 0 and 10, preferably between 0 and 3.

8. The formulation (F) of claim 1, wherein the polyfunctional acrylate is according to formula (III): ##STR00029##

9. The formulation (F) of claim 1, wherein: the solvent is selected from the group consisting of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), 1,3-dimethyl-2-imidazolidinone (DMI), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO) and sulfolane, the photoinitiator is selected from the group consisting of 2,2-dimethoxy-2-phenylacetophenone (DMPA), Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and/or the blocker is selected from the group consisting of avobenzone and 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene.

10. A method for manufacturing a 3D article with an additive manufacturing system, comprising: providing a polymer formulation (F) according to claim 1, and printing layers of the 3D article from the polymer formulation (F), and optionally, curing the 3D article at a temperature ranging from 50 to 450° C.

11. The method of claim 10, wherein the step of printing comprises irradiating the polymer formulation (F) with light.

12. A 3D article obtainable, at least in part, by the method of claim 10.

13. A method of manufacturing 3D objects, wherein the method comprises printing the polymer formulation (F) of claim 1, alone or in combination with other components, and wherein the printing comprises stereolithography (SLA), direct ink writing (DIW), digital light processing (DLP), or inkjet process.

14. A method of Use of the polymer formulation (F) of for coating an article, the method comprising coating or printing the polymer formulation (F) of claim 1, alone or in combination with other components.

15. The formulation (F) of claim 7, wherein R.sup.3 is H or CH.sub.3.

16. The formulation (F) of claim 7, wherein n is between 0 and 3.

17. The method of claim 10, wherein the step of printing comprises irradiating the polymer formulation (F) with UV light or visible light.

Description

EXAMPLES

[0240] Raw Materials

[0241] N,N-dimethylacetamide (DMAc) (anhydrous, 99.8%), potassium carbonate (K.sub.2CO.sub.3) (anhydrous, >99.0%), Celite® 545 filter agent and sodium bicarbonate (NaHCO.sub.3) were purchased from Sigma-Aldrich and used as received. Bisphenol A (BPA, >99%), trimethylolpropane triacrylate (TPM, contains 600 ppm monomethyl ether hydroquinone as inhibitor), acryloyl chloride (>97%, contains 400 ppm of phenothiazine as stabilizer), and 4,4′-dichlorophenyl sulfone (DCPS) were purchased from Aldrich and used as received. Hydrochloric acid, chloroform (HPLC grade), toluene, sodium chloride, methanol, and tetrahydrofuran were purchased from Fisher Chemical and used as received. Diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (>98%) was purchased from TCI as used as received.

[0242] Chloroform-d (CDCl.sub.3) (99.8% atom D) were purchased from Cambridge Isotope Labs and used as received. N-methylpyrrolidone (NMP, BioSolv) and N,N-dimethylformamide (spectrophotometric grade) were purchased from Spectrum and used as received. Triethylamine was purchased from Acros Organics, stirred over calcium hydride (Sigma-Aldrich, 95%) overnight, and then distilled at 90° C. prior to use.

Example 1—Synthesis of Polysulfones Polymers

[0243] Three acrylate-terminated PSU polymers (comparative and inventive) were prepared via a two-step procedure according to Table 1. In step 1, the phenol-terminated PSU polymers were prepared and characterized, as shown in Scheme 1 below. In step 2, the phenol-terminated PSU polymers were converted to the corresponding acrylate-terminated PSU polymers, as shown in Scheme 2 below. The polymers were then characterized by DSC and TGA as detailed below. Results are presented in Table 2 below.

TABLE-US-00001 TABLE 1 Examples Target Mn (g/mol) P1 - Acrylate-terminated PSU 6,000 P2 - Acrylate-terminated PSU 10,000 P3 - Acrylate-terminated PSU 20,000

##STR00021##

##STR00022##

Step 1: Preparation of a Phenol-Terminated PSU Polymers of Mn=20,000 g/Mol

[0244] BPA (52.74 g, 0.2310 mol), DCPS (64.89 g, 0.2260 mol), and potassium carbonate (38.32, 0.2772 mol) were dispersed into anhydrous N,N-dimethylacetamide (400 mL), and toluene (200 mL) within a three-neck, round-bottomed flask fitted with a nitrogen adapter, Dean-Stark trap with a condenser, and a glass mechanical stir rod with a Teflon™ paddle. The heterogenous solution was purged with N.sub.2 for 20 minutes and subsequently heated to 160° C. at which point the reaction was left to reflux for 5 h. The toluene/water azeotrope produced was then drained, and the polymerization was further heated to 180° C. for 12 h, cooled to room temperature, and the resulting solution was filtered through a Celite® to remove salts produced during the course of the polymerization. To protonated the phenol chain ends, the solution was then neutralized using 1 M HCl solution in THF, and final 20,000 Mn PSU polymer was isolated via precipitation into 4 L of MeOH. The resulting white powder was dried in vacuo at 200° C. for 18 h. GPC was used to determine molecular weight.

Step 2: Preparation of Acrylate-Terminated PSU Polymers of Mn=20,000 g/Mol

[0245] The phenol-terminated PSU polymer (60.00 g, 0.003 mol) obtained in step 1 was weighed into a single-neck, round-bottom flask with chloroform (200 mL) and a magnetic stir bar. The resulting solution was then sparged with N.sub.2 for 20 minutes, and triethylamine (5.735 mL, 0.041 mol) was added dropwise at which point the solution was cooled to 0° C. using an ice bath. Acryloyl chloride (2.078 mL, 0.026 mol) was added dropwise to the stirred solution. Upon complete addition, the reaction was allowed to stir at 0° C. for 20 minutes, and then heated to 23° C. where it was allowed to stir for an additional 12 h. The final product was isolated by washing with 2 M aqueous HCl, separating the layers, stirring the organic layer over basic alumina for 1 h followed by washing with 1 M NaOH, sodium bicarbonate solution, and again with brine, 3 times each and drying over MgSO.sub.4 for 2 h followed by precipitation into MeOH to afford a white powder was then dried in vacuo at 50° C. overnight. End group conversion of the phenol chain ends was confirmed by monitoring the peak shifts by .sup.1H NMR. This was done by locating the three peaks that are characteristic of an acrylate at 6.00, 6.31, and 6.59 ppm. In this case, the four benzylic protons used to track the end group previously have shifted and now only two protons are visible so those two are used rather than the four used previously. These two protons do also lie partially under a backbone aromatic peak, which causes the integration to be higher causing an artificially low integration value for the acrylate peaks.

[0246] Characterization of the PSU Polymers

[0247] Gpc 20 mg of PSU was dissolved in 20 mL of chloroform to produce a 1 mg/mL sample. The solution was filtered through a 450 nm PTFE filter into a 1 cm path length quartz cuvette. Dynamic light scattering (DLS) using a Malvern Zetasizer Nano ZS confirmed single chain dissolution in chloroform with no aggregation. The sample was then eluted on Acquity APC XT Columns in a Waters Acquity Advanced Polymer Chromatography system with a 1 mL/min flow rate. The Mn from refractive index was determined by comparison with polystyrene standards at 35° C.

[0248] DSC

[0249] Differential scanning calorimetry with a TA instruments Q1000 elucidated the glass transition temperatures (T.sub.g) with heat/cool/heat cycles at 20/5/20° C./min, respectively. The T.sub.g was taken from the inflection point on the second heat cycle.

[0250] TGA

[0251] Thermogravimetric analysis was performed on a TA Instruments Q50 with N.sub.2 fill gas with a temperature ramp of 10° C./min from 25° C. to 800° C.

TABLE-US-00002 TABLE 2 Target Mn Measured Mn Tg T.sub.d, 5% Examples (g/mol) (g/mol) (° C.) (° C.) P1 6,000 5,700 172 465 P2 10,000 9,300 179 459 P3 20,000 14,600 188 505

Example 2—Formulations Prepared for Photorheology

[0252] Several formulations were prepared according to Table 3 below. 0.36 g of PSU polymers were weighed into 2-dram vials with 0.84 g of NMP. The solutions were mixed with a VWR mini-vortexer until a homogenous solution was achieved. 9 mg of diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (photo-initiator) was added to the solution, as well as TMP (polyfunctional acrylate), the vial covered with aluminum foil, and allowed to mix overnight on a VWR standard analog shaker table. The samples were used within 24 h.

TABLE-US-00003 TABLE 3 Formulations used in Photorheology Assessment Trifunctional Photo- Formu- Polymer Acrylate initiator Solvent lation (g, wt %) (g, wt %) (g, wt %) (g, wt %) CE1 P1 - 0.36, 30 0 0.0092, 2.5 0.84, 70 CE2 P2 - 0.36, 30 0 0.0092, 2.5 0.84, 70 CE3 P3 - 0.36, 30 0 0.0092, 2.5 0.84, 70 E4 P3 - 0.288, 24 0.072, 6 0.0092, 2.5 0.84, 70 E5 P3 - 0.324, 27 0.036, 3 0.0092, 2.5 0.84, 70 E6 P3 - 0.342, 28.5   0.018, 1.5 0.0092, 2.5 0.84, 70 E7 P3 - 0.351, 29.25   0.009, 0.75 0.0092, 2.5 0.84, 70

[0253] Photorheology Experiments: To determine the suitability of a particular formulation for printability, a series photorheology experiments were carried out. For a solution to be processable via vat photo-polymerization a modulus above 30,000 Pa and a G′/G′ crossover time under 2 s is desirable. Photo-rheological experiments were performed on a TA Instruments DHR-2 at 25° C. These measurements were made on a Smart Swap™ geometry with an Omnicure S2000 high-pressure mercury light source with a 320-500 nm filter, 20 mm disposable aluminum parallel plate, and a 20 mm quartz parallel plate lower geometry with a 1000 μm gap. UV intensity was measured using a Silverline radiometer with a 20 mm attachment. Measurement parameters were set with a sampling frequency of 1 Hz, 0.1% strain, and 250 mW/cm.sup.2 UV light intensity. The samples were exposed to UV light 30 s into the experiment for 15 s. The data was analyzed using the TA Instruments TRIOS software to identify the storage modulus (G′), loss modulus (G″), and crossover time.

[0254] Table 4 shows how the molecular weight (Mn) of the polymer affects the printability based on photorheology when the formulations comprise just the polymer and a photo-initiator. While polymers of molecular weight lower than 12,000 g/mol show storage modulus which makes them printable, the polymer of comparative example 3 having a molecular weight of 20,000 g/mol has a too low modulus to a point where it is not printable.

TABLE-US-00004 TABLE 4 Results of printability assessment made using photorheology for formulations of varying molecular weight without trifunctional acrylate. Mn Storage Crossover Examples (g/mol) Modulus (Pa) Time (s) Printability CE1 5,700 82,000 Pa 1.76 s Yes CE2 9,300 45,000 Pa 1.74 s Yes CE3 14,600 18,000 Pa 1.51 s No

[0255] Table 5 shows that adding a trifunctional acrylate makes it possible to obtain high enough modulus to print parts based on photo-rheology for an acrylate-functionalized polysulfone polymer of Mn=20,000 g/mol. It also shows a meaningful improvement in the crossover time.

TABLE-US-00005 TABLE 5 Results of printability assessment made using photorheology for high Mn formulations with trifunctional acrylate Mn Wt. % Storage Crossover Examples (g/mol) TMP Modulus (Pa) Time (s) Printability CE3 14,600 0 18,000 1.51 No E4 14,600 2.5 31,000 1.23 Yes E5 14,600 5 37,000 1.23 Yes E6 14,600 10 56,000 1.20 Yes E7 14,600 20 280,000 1.39 Yes

Example 3—Formulations Used in Vat Photopolymerization

[0256] A formulation according to the invention was prepared by dissolving the polymer P3 (27.552 g, 23.85 wt %), the TMP (6.888 g, 5.96 wt %), diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide photo-initiator (0.706 g, 0.612 wt %), into NMP (80.36 g, 69.57%).

[0257] A part was fabricated with a laser-based VP apparatus.

[0258] Laser-Based VP Apparatus:

[0259] A 405 nm UV laser and optical train was extracted from Formlabs 1+ and used for delivering UV irradiation to the resin surface. An aluminum vat was used to contain the resin during the printing process. A stainless steel build stage with glass build platform was used as the stage for part fabrication. A stainless-steel rotary recoating system was used to recoat resin on the build platform.

[0260] Printing Method

[0261] 65 ml of the formulation was transferred into the aluminum vat and the build platform was located at the focal plane of the projector. After a brief dipping step, the build platform was positioned at a depth of 1-layer thickness from the resin surface. The rotary recoating blade was then used to smoothen the resin surface and from a meniscus-free later. A pattern corresponding to the layer-to-be-fabricated was rastered on the resin surface at a predetermined number of passes, laser power, and scan-speed. These steps were repeated until part completion.

[0262] PreForm 2.3.3 was used to slice the STL file into 120 micron layers. A custom Python program was used to control the apparatus and printing process.

[0263] A hexagonal open lattice with a pillar wall thickness of 750 microns, side walls of size 2 mm height of 24 mm, width of 17 mm and length of 28 mm was constructed in Netfabb and extruded to a height of 24 mm to create the reference geometry.

[0264] Printing Results

[0265] Printing Parameters: [0266] Layer thickness=120 microns [0267] Intensity=20 mW [0268] Scan Speed=1550 mm/s [0269] #of passes per layer=1

[0270] Feature Resolution: Hexagonal walls were visible on the part height. Average wall thickness was around 2 mm.

[0271] Addition of TMP increased the modulus of the cured gel, thus forming a self-supporting structure faster than a TMP-free formulation.