Ring Opening Copolymerization of Four-Dimensional Printed Shape Memory Polyester Photopolymers Using Digital Light Processing

Abstract

The advent of smart or functional 3D printing (3DP) materials (“four-dimensional (4D) materials”) represents one important development toward addressing current limitations in medicine, aerospace, and other fields. Here, we report on how the ring opening copolymerization (ROCOP) of readily available and well-known anhydrides and epoxides may be used to produce a library of polyesters that are capable of being leveraged in thiol-ene photopolymer resins for processing by stereolithography or digital light processing. These polyesters display a 4D behavior (shape memory), can be processed into complex 3D structures readily, and display robust mechanical properties including elastic moduli greater than 600 MPa (with corresponding strains at break of 52.5%). These materials, with their advanced properties and robust mechanical behaviors, represent a significant advancement in the quest for 4D printing materials.

Linalool Derivatives for Natural Product-Based 4D Printing Resins

“…Dynamic mechanical analysis (DMA) was conducted using protocols described earlier. 29 In short, DMA bars were tested in tension (1 Hz, 0.01 N preload) from −50 to 150 °C at 2 °C × min −1 . Thermogravimetric analysis (TGA) of 10 mg samples was conducted from room temperature to 1000 °C at 10 °C × min −1 , with a flow rate of 100 mL × min −1 nitrogen atmosphere.…”

“…Photopolymer resins for DLP printing were prepared as previously described . For the HDI linalool resin, 25 g HDI linalool (0.052 mol) were added to a brown glass vial followed by 25.65 g PETMP (0.052 mol) and 10 g propylene carbonate (20 wt % of total reactive resin mass).…”

“…Dynamic mechanical analysis (DMA) was conducted using protocols described earlier . In short, DMA bars were tested in tension (1 Hz, 0.01 N preload) from −50 to 150 °C at 2 °C × min –1 .…”

“…Photopolymer resins for DLP printing were prepared as previously described. 29 For the HDI linalool resin, 25 g HDI linalool (0.052 mol) were added to a brown glass vial followed by 25.65 g PETMP (0.052 mol) and 10 g propylene carbonate (20 wt % of total reactive resin mass). These were mixed until a homogeneous resin was produced, at which point 0.5 wt % Irgacure 819 and 0.25 wt % luetin oleoresin were added.…”

“…Terpenes have found use in a variety of different polymeric applications, including the development of degradable polyesters and polycarbonates, high T g and performance polymers, and even as initiators or monomers in controlled polymerizations. − The successful utilization of terpenes has generally required modifications to terpenoids or terpenes, such as limonene oxide produced from d -limonene or with epoxidized soybean oils. − Often this yields polymers with degradable backbones, such as with polyesters and polycarbonates synthesized from limonene oxide; the common alternative is the formation of degradable side chains after functionalization with acrylates. ,− More recently, this second strategy has been exploited toward 3D printing of natural products, making use of the available functional groups for modification followed typically by free radical crosslinking to produce nondegradable backbones. − For example, retinol has been conjugated with poly­(vinyl alcohol) for drug delivery applications, cyclodextrane has been functionalized with acrylate groups for vat photopolymerization, linalool and citronellol were grafted to oligomeric chitosan, , and myrcenol has been projected toward producing functional copolymers and brushes . However, there are other strategies toward photopolymerization 3D printing, such as thiol-ene chemistry, which has been widely utilized for postfabrication functionalization but only sparingly used for additive manufacturing. ,− …”