3D printing of recyclable dynamic covalent boronate ester-based polymers

Abstract

The development of 3D printing or additive manufg. has grown rapidly in the past decade, which calls for more sustainable photoresins to accommodate the increasing demand of the future 3D printed products. In particular, stereolithog. (SLA) 3D printing have been demonstrated as an efficient method to produce high-accuracy and isotropic parts using either com. available or custom-made photoresins with fine features and smooth surface finish. Herein, we demonstrate a new method to print boronate-ester contg. polymer in 3D by locally activating a photobase using an SLA system. Because the lack of toxicity and the ability to anticipate reversible dynamic covalent bonding, boronic acid-contg. macromols. have been utilized in nos. of biomedical applications, such as mol. sensing, thermoresponsive hydrogels, drug delivery, and cell capture and release; however, their potentials in 3D printing has not yet been explored. In our study, we have incorporated a polymer derived from 3-acrylamidophenylboronic acid and a tetra-1,2 diol functionalized mol. to demonstrate the recyclability of the 3D printed materials. In our system, upon photoactivation the photobase increase the local pH to be great than its pKa, the boronic acids then form boronate ester with 1,2-diols to create a highly crosslinked network. This esterification process can also be reversed once being exposed to an acidic environment. We have performed mech. characterization on the bulk boronate ester-based polymers and show the feasibility of purifying and reusing the depolymd. materials in the proceeding printing cycles.