Continuous Additive Manufacturing using Olefin Metathesis

Abstract

The development of chemistry is reported to implement selective dual-wavelength olefin metathesis polymerization for continuous additive manufacturing (AM). A resin formulation based on dicyclopentadiene is produced using a latent olefin metathesis catalyst, various photosensitizers (PSs) and photobase generators (PBGs) to achieve efficient initiation at one wavelength (e.g., blue light) and fast catalyst decomposition and polymerization deactivation at a second (e.g., UV-light). This process enables 2D stereolithographic (SLA) printing, either using photomasks or patterned, collimated light. Importantly, the same process is readily adapted for 3D continuous AM, with printing rates of 36 mm h^-1 for patterned light and up to 180 mm h^-1 using un-patterned, high intensity light.

Keywords: additive manufacturing; dual-wavelength; olefin metathesis; photosensitizer; stereolithography.

Figure 1

General overview of SWOMP chemistry using HM as the catalyst and DCPD as the monomer. a) Irradiation at λ ₁ initiates the catalyst via photosensitization, while b) generation of amine base by PBG photolysis at λ ₂ decomposes the catalyst and deactivates polymerization. c) Formulation components used in optimized photoresin. PC, photo‐cage; SIMes, 1,3‐Bis(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene; CQ, camphorquinone; EDAB, ethyl‐4‐(dimethylamino) benzoate; TMG, 1,1,3,3‐tetramethyl guanidine; NPPOC, 3‐nitrophenylpropyloxycarbonyl; DCPD, dicyclopendatiene.

Figure 2

Optimized photoresin for SWOMP. a) Generalized schematic of photoinitiation and photo‐decomposition chemistries promoted by blue or UV light, respectively. b) UV–vis spectra demonstrating the photo‐orthogonality of the photosensitization (CQ, light blue spectrum) and photo‐decomposition (NPPOC‐TMG, purple spectrum) chemistries employed. Spectra were collected for the individual compounds at 0.01 mg mL^–1 in CH₂Cl₂ solution. c) Polymerization kinetics as measured by FT‐IR spectroscopy at 1573 cm^–1 for optimized photoresin irradiated with 475 nm light in the absence of PBG (black circles) and with PBG at 475 nm (blue circles), 365 nm (purple circles), and both wavelengths (orange circles). d) Evolution of modulus over time for the same resin formulation and irradiation wavelengths as in (c). e) Polymerization deactivation by turning on the 365 nm light at different times (t = 0, 45, 60, 75, 90, or 105 s) after initiation as compared to polymerization in the absence of 365 nm light (blue). The dashed lines represent the time at which the 365 nm light was turned on with the various colors corresponding to the separate kinetic traces as measured by FT‐IR. The 475 nm light was turned on at t = 0 s and was left on throughout the duration of the experiments. [DCPD]/[NPPOC‐TMG]/[HM] = 5000:10:1 was used for these experiments with 0.5 wt.% CQ and 1 wt.% EDAB.

Figure 3

Summary of single wavelength SWOMP. a) Schematic of photopolymerization setup, wherein patterned blue light was projected into the photoresin from below. b) Optical photograph of PDCPD dogbones produced from the image shown above. c) DMA of PDCPD films prepared via SWOMP using the optimized resin with (blue circles) or without (back circles) 15 equiv of NPPOC‐TMG relative to HM. D) Measured tensile strengths (blue bars) and Young's moduli (purple shaded bars) of dogbones prepared by photopolymerization using the optimized resin and different amounts of NPPOC‐TMG. e) Schematic of projector image and resulting cured staircase structure used to determine cure depths. f) Measured cure depths obtained via photopolymerization by varying the projected light intensity and using optimized DCPD resins containing 0 (black circles), 5 (purple circles), 10 (orange circles), or 15 (blue circles) equiv of NPPOC‐TMG relative to HM. [DCPD]/[NPPOC‐TMG]/[HM] = 5000:15:1 was used for these experiments with 1 wt.% CQ and 2 wt.% EDAB.

Figure 4

Summary of dual‐wavelength SWOMP. a) Schematic of setup for intensity‐patterned photopolymerization, wherein patterned, gray‐scaled blue light is superimposed with collimated UV light and projected into the resin to create a 3D object. b) Deactivation height as a function of UV/blue light intensity ratio for resins formulated with 5 (purple circles), 10 (orange circles), or 15 equiv (blue circles) of NPPOC‐TMG relative to HM. c,d) Multi‐level intensity images and corresponding topographical images of printed objects showing the heights of the different surface features. The inset in (d) is an optical image of the printed part. e) Measured (blue circles) and expected (black line) heights for the surface features obtained for the object in (d). The red line on the topographical image in (d) represents the profile path. Expected heights were calculated by subtracting the average deactivation height found in B from the spacer thickness (i.e., 635 µm) and lateral distances were scaled to match measured values. [DCPD]/[NPPOC‐TMG]/[HM] = 5000:15:1 was used for these experiments with 1 wt.% CQ and 2 wt.% EDAB.

Figure 5

Additional SWOMP of “National” text, showcasing the multi‐dimensional precision of deactivation using multi‐intensity blue light patterning. a) Multi‐layer grayscale image and corresponding topographical image of tapered height “National” text. The grid represents 1 mm × 1 mm squares. b) Grayscale representation of the relative blue light intensities projected. c) Measured (blue circles) and expected (black line) heights for the surface features obtained for the object in (a). The red line on the topographical image in (a) represents the profile path. Expected heights were calculated by subtracting the deactivation height found using an exponential fit of the deactivation data from the spacer thickness (i.e., 500 µm) and lateral distances were scaled to match measured values. [DCPD]/[NPPOC‐TMG]/[HM] = 5000:15:1 was used for these experiments with 1 wt.% CQ and 2 wt.% EDAB.

Figure 6

Summary of continuous SWOMP. a) Schematic of setup for continuous SLA, wherein patterned blue light is superimposed with collimated UV light and projected into the resin and an object forms on the build head, which becomes progressively taller as the build head is withdrawn. b) Optical image of a Thunderbird object obtained using a continuous SWOMP projector setup at a printing rate of 36 mm h^–1. c–e) Photographs of cylindrical object obtained using a high‐intensity lamp setup and a printing rate of 180 mm h^–1 during printing (c), immediately after printing (d), and inverted after removing from the printer (e). [DCPD]/[NPPOC‐TMG]/[HM] = 5000:15:1 was used for these experiments with 1 wt.% CQ and 2 wt.% EDAB.