Digital Light Processing of Thermoplastic Poly(methyl methacrylate) Photoresin Combined With Solvent Vapor Smoothing

3D printing of complex geometries remains limited by the trade‐off between printing resolution and surface quality: fused deposition modeling allows efficient solvent‐based surface smoothing but offers limited resolution, whereas vat‐photopolymerization provides high resolution but typically uses crosslinked thermosets that restrict solvent‐induced surface reflow. Here, we present a poly(methyl methacrylate) (PMMA)‐based photoresin, formulated from polymeric PMMA, methyl methacrylate, and butyl methacrylate, that enables high‐resolution digital light processing (DLP) while retaining thermoplastic characteristics. A wax additive suppressed rapid monomer evaporation, enabling stable printing on a benchtop DLP system. Incorporating 15 wt% butyl methacrylate prevented visible solvent‐induced cracking over 14 days, and a 50:50 (v/v) acetone:2‐propanol mixture gave effective smoothing after 120 min. This approach reduced the staircase‐induced surface roughness from 2.33 µm to 129 nm (86 × 86 µm 2 evaluation area), while local measurements on treated microlenses (10 × 10 µm 2 ) yielded S q = 12.8 ± 4.4 nm. The optical transmittance of 2 mm thick samples increased from approximately 30% to 80% in the visible range. The presented strategy combines high‐resolution vat‐polymerization with effective surface smoothing and provides a viable route towards smooth and optically transparent PMMA components, particularly for illumination optics and applications requiring complex geometries.