The Influence of Vat Photopolymerization Processing Parameters on Semicrystalline Morphology

Understanding how processing parameters influence the crystalline morphology of semicrystalline photopolymers is critical for optimizing their performance in vat photopolymerization (VP)-based additive manufacturing. This study examined the effects of photoabsorber (PA) concentration, light intensity, layer thickness, and post-VP annealing temperature on the crystallite size distribution and crystallization rate in a thiol–ene-based semicrystalline polymer system composed of pentaerythritol tetrakis(3-mercaptopropionate) (5 mol %), 1,6-hexanedithiol (90 mol %), and diallyl terephthalate (100 mol %), with Sudan I as the PA. Polarized optical microscopy (POM) combined with image segmentation was used to quantify morphological features related to crystallinity, while differential scanning calorimetry, tensile testing, and dynamic mechanical analysis established correlations between morphology and bulk properties. Increasing PA concentration reduced the effective photopolymerization rate by absorbing part of the incident UV light, resulting in higher percent crystallinity, larger mean crystallite sizes, and broader size distributions. In contrast, higher light intensities accelerated curing, yielding more amorphous regions and smaller crystallites due to nonlinear light attenuation. Samples fabricated with thicker (150 μm) layers showed superior mechanical properties after annealing compared to thinner (50 μm) layers, underscoring the link between morphology, processing, and macroscopic properties. Hot-stage POM revealed that larger, heterogeneously sized crystals recrystallized into smaller, more uniform structures upon melting and cooling. These finer crystallites created physical cross-links, reducing stress localizations and improving material flexibility. Overall, these findings advance the understanding of the influence of VP processing parameters on nucleation, growth, and morphology in semicrystalline polymers and can provide insights into the design of materials with tunable properties for additive manufacturing.