Influence of irradiation process and RAFT-mediated photopolymerization on polymer network structure: a comparison between 3D-printed objects and cured films

This study investigates the influence of curing conditions—comparing 3D printing and continuous irradiation—on the microstructure and thermomechanical properties of photopolymers. Using Real-Time Fourier Transform Infrared spectroscopy (RT-FTIR), photo-differential scanning calorimetry (photoDSC), and dynamic mechanical analysis (DMA), differences in polymerization kinetics were characterized and their effects on polymer structure assessed. The layer-by-layer exposure used in 3D DLP printing generates reactive species differently than continuous irradiation, leading to a less homogeneous polymer network. These structural differences are particularly pronounced when the monomers exhibit steric hindrance. The addition of RAFT agents proved effective in mitigating these disparities: photopolymers synthesized under RAFT-control achieved comparable conversion and thermomechanical properties regardless of the irradiation conditions. These findings provide insight into how polymerization kinetics and structure are influenced by the fabrication process and demonstrate the potential of RAFT-mediated strategies to enhance the structure homogeneity of 3D-printed photopolymers.