Photopolymerizable semicrystalline thermoplastics resulting from thiol–ene polymerizations were formed via fast polymerizations and achieved excellent mechanical properties. These materials have been shown to produce materials desirable for additive manufacturing (3D printing), especially for recyclable printing and investment casting. However, while well-resolved prints were previously achieved with the thiol–ene thermoplastics, the remarkable elongation at break ( ε max ) and toughness ( T ) attained in bulk were not realized for 3D printed components ( ε max,bulk ∼ 790%, T bulk ∼ 102 MJ m −3 vs. ε max,print < 5%, T print < 0.5 MJ m −3 ). In this work, small concentrations (5–10 mol%) of a crosslinker were added to the original thiol–ene resin composition without sacrificing crystallization potential to achieve semicrystalline, covalently crosslinked networks with enhanced mechanical properties. Improvements in ductility and overall toughness were observed for printed crosslinked structures, and substantial mechanical augmentation was further demonstrated with post-manufacture thermal conditioning of printed materials above the melting temperature ( T m ). In some instances, this thermal conditioning to reset the crystalline component of the crosslinked prints yielded mechanical properties that were comparable or superior to its bulk counterpart ( ε max ∼ 790%, T ∼ 95 MJ m −3 ). These unique photopolymerizations and their corresponding monomer compositions exhibited concurrent polymerization and crystallization along with mechanical properties that were tunable by changes to the monomer composition, photopolymerization conditions, and post-polymerization conditioning. This is the first example of a 3D printed semicrystalline, crosslinked material with thermally tunable mechanical properties that are superior to many commercially-available resins.
more »
« less
Volumetric Printing of Thiol‐Ene Photo‐Cross‐Linkable Poly(ε‐caprolactone): A Tunable Material Platform Serving Biomedical Applications
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
- NSF-PAR ID:
- 10403046
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials
- Volume:
- 35
- Issue:
- 19
- ISSN:
- 0935-9648
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract We report the facile synthesis and 3D printing of a series of triblock copolymers consisting of soft and hard blocks and demonstrate that alkene pendant groups of the hard block can be covalently modified. The polymers are prepared using a salenCo(III)TFA/PPNTFA binary catalyst system and 1,2‐propanediol as a chain transfer agent, providing an efficient one‐pot, two‐step strategy to tailor polymer thermal and mechanical properties. Thixotropic inks suitable for direct ink write printing were formulated by dissolving the block copolymers in organic solvent and dispersing NaCl particles. After printing, porous structures were produced by removing solvent and NaCl with water to give printed structures with surfaces that could be modified via UV‐initiated thiol‐ene click reactions. Alternatively, a tetra‐thiol could be incorporated into the ink and used for cross‐linking to give objects with high solvent resistance and selective degradability.
-
more » « less
Abstract We report the facile synthesis and 3D printing of a series of triblock copolymers consisting of soft and hard blocks and demonstrate that alkene pendant groups of the hard block can be covalently modified. The polymers are prepared using a salenCo(III)TFA/PPNTFA binary catalyst system and 1,2‐propanediol as a chain transfer agent, providing an efficient one‐pot, two‐step strategy to tailor polymer thermal and mechanical properties. Thixotropic inks suitable for direct ink write printing were formulated by dissolving the block copolymers in organic solvent and dispersing NaCl particles. After printing, porous structures were produced by removing solvent and NaCl with water to give printed structures with surfaces that could be modified via UV‐initiated thiol‐ene click reactions. Alternatively, a tetra‐thiol could be incorporated into the ink and used for cross‐linking to give objects with high solvent resistance and selective degradability.
-
Levoglucosan is a renewable chemical obtained in high yields from pyrolysis of cellulosic biomass, which offers rich functionality for synthetic modification and crosslinking. Here, we report the facile and scalable synthesis of a family of biobased networks from triallyl levoglucosan and multifunctional thiols via UV-initiated thiol–ene click chemistry. The multifunctional thiols utilized in this study can also be sourced from renewable feedstocks, leading to overall high bio-based content of the synthesized levoglucosan networks. The thermomechanical and hydrolytic degradation properties of the resultant networks are tailored based on the type and stoichiometric ratio of thiol crosslinker employed. The Young's modulus and glass transition temperature of levoglucosan-based networks are tunable over the wide ranges of 3.3 MPa to 14.5 MPa and −19.4 °C to 6.9 °C, respectively. The levoglucosan-based thermosets exhibit excellent thermal stability with Td,10% > 305 °C for all networks. The suitability of these resin formulations for extrusion-based 3D printing was illustrated using a UV-assisted direct ink write (DIW) system creating 3D printed parts with excellent fidelity. Hydrolytic degradation of these 3D printed parts via ester hydrolysis demonstrated that levoglucosan-based resins are excellent candidates for sustainable rapid prototyping and mass production applications. Overall, this work displays the utility of levoglucosan as a renewable platform chemical that enables access to tailored thermosets important in applications ranging from 3D printing to biomaterials.more » « less
-
Three-dimensional (3D) bioprinting is important in the development of complex tissue structures for tissue engineering and regenerative medicine. However, the materials used for bioprinting, referred to as bioinks, must have a balance between a high viscosity for rapid solidification after extrusion and low shear force for cytocompatibility, which is difficult to achieve. Here, a novel bioink consisting of poly(ethylene glycol) (PEG) microgels prepared via off-stoichiometry thiol–ene click chemistry is introduced. Importantly, the microgel bioink is easily extruded, exhibits excellent stability after printing due to interparticle adhesion forces, and can be photochemically annealed with a second thiol–ene click reaction to confer long-term stability to printed constructs. The modularity of the bioink is also an advantage, as the PEG microgels have highly tunable physicochemical properties. The low force required for extrusion and cytocompatibility of the thiol–ene annealing reaction also permit cell incorporation during printing with high viability, and cells are able to spread and proliferate in the interstitial spaces between the microgels after the constructs have been annealed. Overall, these results indicate that our microgel bioink is a promising and versatile platform that could be leveraged for bioprinting and regenerative manufacturing.more » « less
