Boronate Esters Dynamic Networks for the Reduction of Mechanical Anisotropy in Vat 3D Printed Manufacts.

Abstract

Vat photopolymerization (VP) is a prominent 3D printing technique known for its high resolution and precision. However, mechanical anisotropy can limit the performance of printed structures by making their mechanical properties dependent on the printing orientation and curing conditions. This study introduces a photocurable material for VP 3D printing, combining dynamic boronate ester-based cross-linking with nondynamic cross-links. The material is synthesized using photoinduced free radical polymerization of a (meth)acrylate-based formulation, incorporating a diboronate ester with two methacrylate functionalities (DBEDMA) and a commercial poly(propylene glycol) diacrylate (PPGDA). The resulting resins exhibit rapid curing kinetics, low shrinkage (5-8%), and tailored viscoelastic properties. Stress relaxation and creep recovery studies highlight the role of boronate ester metathesis in enabling network rearrangement and stress dissipation. The optimal formulation, 40D60P, shows a significant reduction in mechanical anisotropy compared to an equivalent conventional resin containing only static cross-links (40B60P). Tensile tests confirm higher toughness and more consistent stress-strain behavior across printing orientations, attributed to partial topological rearrangement enabled by the dynamic cross-links. While improvements in isotropy are evident, a certain degree of mechanical anisotropy remains under specific conditions due to the presence of static cross-linking. Surface analysis via optical microscopy reveals smoother patterns in dynamic resin specimens, corroborating mechanical findings. This work demonstrates the potential of boronate ester-based dynamic chemistry to enhance the performance of VP 3D-printed materials, particularly in applications where reduced anisotropy and improved mechanical properties are critical.