Radical-Mediated Ring-Opening Photopolymerization for Semicrystalline Thermoplastic Additive Manufacturing

Abstract

Conventional approaches to stereolithographic additive manufacturing (SLA) employ liquid resin formulations based on multifunctional (meth)acrylates and epoxides that afford cross-linked polymeric networks upon polymerization. Nevertheless, the utilization of resins that yield semicrystalline thermoplastics provides facile access to physical and mechanical properties that are otherwise difficult to attain, such as high toughness and resistance to solvent swelling as well as additional postfabrication processing options that can be used to extend the life cycle of three-dimensional printed polymers. Here, we report the SLA-based additive manufacturing of semicrystalline thermoplastics utilizing the radical-mediated ring-opening photopolymerization of seven- and eight-membered cyclic allylic sulfides. Photopolymerization of resin formulations incorporating seven- and eight-membered cyclic allylic sulfides and crystallization of the resultant (co)polymers were examined using Fourier transform infrared spectroscopy, photorheology, and isothermal photo-differential scanning calorimetry. The formulated resins were found to polymerize and subsequently crystallize rapidly upon irradiation under ambient conditions. The mechanical properties of stereolithographically printed copolymers approached the bulk copolymer mechanical properties, demonstrating unusually strong interlayer adhesion atypical of layerwise, stereolithographic printing of semicrystalline polymers. Finally, high-quality, recyclable, semicrystalline thermoplastic parts were printed and melted down, demonstrating the potential for these semicrystalline materials to provide a path for improved sustainability of polymeric parts produced via SLA.

From Unregulated Networks to Designed Microstructures: Introducing Heterogeneity at Different Length Scales in Photopolymers for Additive Manufacturing

“…Thiol-ene concepts have become an important example of semicrystalline photopolymers, which have also been printed in a stereolithographic process (Figure a). , Very recently a thiol-ene monomer system has been claimed to form a linear semicrystalline thermoplastic material with outstanding mechanical properties . Furthermore, radical ring-opening of cyclic allyl sulfides photopolymerization to obtain semicrystalline photopolymers has been successfully used in SL (Figure b) . These efforts have recently been translated to cationic ring-opening photopolymerization at elevated temperatures by our group, which exhibited shape-memory behavior (Figure c) .…”

“…(b) Semicrystalline radical ring-opened photopolymer networks characterized by SAXS. Reprinted (adapted) with permission from ref . Copyright 2023 American Chemical Society.…”

The Future of Free Radical Polymerizations

“…Ellis’s group synthesized nucleic acid mimicking polymers via FRP from nucleotide-containing peptide-hybrid monomers . Cyclic vinyl monomers that can undergo radical ring-opening polymerization (rROP) have been explored to afford semicrystalline thermoplastics via stereolithographic additive manufacturing and degradable polymer nanoparticles with spherical morphology . Yang et al developed condensed droplet radical polymerization technique to facilely fabricate nonspherical polymer nanoparticles with controlled morphology, which can also be attainable via a polymerization-induced self-assembly approach. , …”