3D‐printed polymer blends with programmable mechanical and compositional heterogeneity were fabricated using grayscale digital light processing by spatially modulating the intensity of light during printing and swelling the resulting part with a second monomer. A rubbery poly(ethylene glycol) diacrylate functionally graded print is variably swollen with acrylamide monomer as a function of crosslinking density. Following a secondary polymerization, a 3D‐printed functionally graded blend with regions of varying composition and stiffness was formed. A deterministic model for polymer conversion informs printing conditions to correspond with predicted material properties based upon local volume fractions of the two materials. Upon the secondary polymerization, two networks are present within the printed structure including glassy and rubbery regions. The compressive moduli of local regions within prints ranges from 76 to 200 MPa and measured moduli of the structures agree with predicted values acquired using finite element analysis. A lattice structure with prescribed local stiffness printed using grayscale exposures deforms differentially when compressed. Advantageously, local dimensional deformations caused by the removal of the unreacted printing monomer are eliminated due to the introduction of the second polymer. This method provides predictive control over local mechanical properties and high shape precision while maintaining the simplicity of vat photopolymerization.
- Award ID(s):
- 1809841
- NSF-PAR ID:
- 10187897
- Date Published:
- Journal Name:
- Polymer Chemistry
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 1759-9954
- Page Range / eLocation ID:
- 39 to 46
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Photopolymerization is a ubiquitous, indispensable technique widely applied in applications from coatings, inks, and adhesives to thermosetting restorative materials for medical implants, and the fabrication of complex macroscale, microscale, and nanoscale 3D architectures via additive manufacturing. However, due to the brittleness inherent in the dominant acrylate‐based photopolymerized networks, a significant need exists for higher performance resin/oligomer formulations to create tough, defect‐free, mechanically ductile, thermally and chemically resistant, high modulus network polymers with rapid photocuring kinetics. This study presents densely cross‐linked triazole‐based glassy photopolymers capable of achieving preeminent toughness of ≈70 MJ m−3and 200% strain at ambient temperature, comparable to conventional tough thermoplastics. Formed either via photoinitiated copper(I)‐catalyzed cycloaddition of monomers containing azide and alkyne groups (CuAAC) or via photoinitiated thiol‐ene reactions from monomers containing triazole rings, these triazole‐containing thermosets completely recover their original dimensions and mechanical behavior after repeated deformations of 50% strain in the glassy state over multiple thermal recovery–strain cycles.
-
null (Ed.)The development of tunable and degradable crosslinked-polyanhydride networks from renewably derived itaconic anhydrides and multifunctional thiols is presented. Itaconic acid was initially converted to ethyl itaconic anhydride and isoamyl itaconic anhydride via a two-step synthetic procedure on hundred-gram scale with minimal purification. Dinorbornene-functionalized derivatives were prepared via cycloaddition chemistry, and photoinitiated thiol–ene polymerization reactions were explored using commercially available tetra- and hexa-functional thiols, all using solvent-free syntheses. The thiol–ene reaction kinetics of different monomer compositions were characterized by real-time Fourier transform infrared (RT-FTIR) spectroscopy, with the norbornene functionalized derivatives exhibiting the highest reactivity towards thiol–ene photopolymerizations. The thermal and mechanical characteristics of the thermosets were analyzed and the viscoelastic behavior was investigated by dynamic mechanical analysis to understand the influence of the ester functionality and choice of crosslinker on the material properties. The anhydride backbone was found to be susceptible to controlled degradation under physiologically-(phosphate-buffered saline) and environmentally-relevant (artificial seawater) testing conditions over a period of 60 days at 50 °C. This work demonstrates that itaconic acid may be a useful feedstock in the generation of degradable polyanhydride networks via thiol–ene photopolymerization.more » « less
-
Abstract Current thoroughly described biodegradable and cross‐linkable polymers mainly rely on acrylate cross‐linking. However, despite the swift cross‐linking kinetics of acrylates, the concomitant brittleness of the resulting materials limits their applicability. Here, photo‐cross‐linkable poly(ε‐caprolactone) networks through orthogonal thiol‐ene chemistry are introduced. The step‐growth polymerized networks are tunable, predictable by means of the rubber elasticity theory and it is shown that their mechanical properties are significantly improved over their acrylate cross‐linked counterparts. Tunability is introduced to the materials, by altering
M c(or the molar mass between cross‐links), and its effect on the thermal properties, mechanical strength and degradability of the materials is evaluated. Moreover, excellent volumetric printability is illustrated and the smallest features obtained via volumetric 3D‐printing to date are reported, for thiol‐ene systems. Finally, by means of in vitro and in vivo characterization of 3D‐printed constructs, it is illustrated that the volumetrically 3D‐printed materials are biocompatible. This combination of mechanical stability, tunability, biocompatibility, and rapid fabrication by volumetric 3D‐printing charts a new path toward bedside manufacturing of biodegradable patient‐specific implants. -
Abstract The interfacial region in composites that incorporate filler materials of dramatically different modulus relative to the resin phase acts as a stress concentrator and becomes a primary locus for composite failure. A novel adaptive interface (AI) platform formed by coupling moieties capable of dynamic covalent chemistry (DCC) is introduced to the resin–filler interface to promote stress relaxation. Specifically, silica nanoparticles (SNP) are functionalized with a silane capable of addition fragmentation chain transfer (AFT), a process by which DCC‐active bonds are reversibly exchanged upon light exposure and concomitant radical generation, and copolymerized with a thiol‐ene resin. At a fixed SNP loading of 25 wt%, the toughness (2.3 MJ m−3) is more than doubled and polymerization shrinkage stress (0.4 MPa) is cut in half in the AI composite relative to otherwise identical composites that possess a passive interface (PI) with similar silane structure, but without the AFT moiety. In situ activation of the AI during mechanical loading results in 70% stress relaxation and three times higher fracture toughness than the PI control. When interfacial DCC was combined with resin‐based DCC, the toughness was improved by 10 times relative to the composite without DCC in either the resin or at the resin–filler interface.