(576i) Network Engineering Toward Tunable Architecture and Mechanics Using Lignin-Derivable Diacrylates

Aromatic-based thermosetting polymers with structural rigidity and thermal stability are desirable for high-performance applications. Among various feedstocks, lignin-derivable (bis)phenolics are more favorable than petroleum-derived counterparts with potentially higher sustainability and less toxicity. Moreover, their inherent aromatic structure and the diversity of functional groups allow versatile pathways for the generation of high-performance thermosets. (Meth)acrylate thermosets, which are widely applied in coatings and additive manufacturing resins, usually exhibit material fracturing after curing with the incorporation of aromatic building blocks. Studies have shown tunable thermomechanical properties with varied architecture in epoxies, yet only a few of them focused on network engineering (meth)acrylates to modify the fracturing issues. To address these challenges, we fabricate acrylate thermosets by photopolymerization of lignin-derivable vanillyl/bisguaiacol F diacrylates (VDA/BGFDA) with a bio-derivable n-butyl acrylate (BA) as the reactive diluent at different compositions. This strategy enables tuning of the network architecture with variations in both aromatic content and the distance between crosslinks. Increasing the amount of diacrylate in both VDA/BA and BGFDA/BA networks led to a higher storage modulus at 25 ºC, but also led to higher network inhomogeneity, which comprises unreacted groups and inhomogeneous crosslink density, suggested by lower acrylate conversions and broad, complex thermal transitions. Additionally, an increase in the aromatic content (monoaromatic VDA to bisaromatic BGFDA) led to higher inhomogeneity. To extend the effect of aromatic content on network architecture, a mixture of the two lignin-derivable diacrylates resulted in the lowest conversion and a biphasic-like thermal transition corresponding to VDA and BGFDA-regions. This approach highlights a promising strategy for tuning thermomechanical properties of thermosets with handles on the aromatic content and the crosslink density that control network architectures. Overall, the fundamental understanding of the connection between molecular structure, network architecture, and mechanics establishes a guideline for designing high-performance lignin-derivable vinyl ester-based thermosets with tailored thermomechanical properties.