Photocurable vitrimers with malleable and self-healing trade-off enabled by manipulating dynamic boronic ester bonds

Abstract

Although numerous strategies refer to dynamic covalent bond exchanges of small molecules for self-repairing thermosets, it remains a critical challenge to be able to jointly tune the malleability and dynamic properties of photocurable materials via extending dynamical small molecule bridging chains with tunable kinetic features. Herein, we successfully synthesized two typical diboronic ester molecules (diboronic ester dithiol/diacid) with variable dioxaborolane metathesis kinetics, which acted as dynamical interlinking segments constructing simple hydrogenated bisphenol A (HBA) epoxy backbone to achieve dynamically cross-linking feature. Subsequently, the acrylate- and anhydride-modified HBA vitrimers bearing diboronic ester-extending segment variants and photocuring traits are successfully synthesized by a one-pot reaction. Consequently, it is demonstrated that the embedded amounts of dynamic diboronic ester bonds in the backbone play a key role in the photopolymerization rate of photocurable vitrimers. The photopolymerization rate decreases significantly as more diboronic ester segments. Moreover, the diboronic ester dithiol-mediated photocurable vitrimer (HBA-S) exhibits enhanced malleability (strain at break of 26.6 %), desirable photo-crosslinked network, and accelerated thermal-triggered self-healing ability (scratch self-healing efficiency of closing to 100 % at 150 °C), compared to those of the diboronic ester diacid-mediated vitrimer (HBA-O) under identical conditions. This work validates the probability of transferring the dioxaborolane metathesis of small molecules to dynamic properties of bulk UV-curing materials, which provides valuable guidance for the rational design and fabrication of tunable dynamic photocurable materials.