Time-Resolved Gelation of Photopolymerizable Melts

The production of advanced materials by additive manufacturing and photolithography relies on controlled transitions from soluble to insoluble states that form three-dimensional polymer networks. In polymer systems, this liquid–solid transformation, or gelation, determines the final mechanical properties. Conventional methods to characterize gelation provide the empirical exposure–depth relationship that reflects the apparent curing threshold but lack the temporal resolution to capture continuous network evolution. As precision manufacturing demands rise, especially in photoresist applications, there is a growing need for techniques that resolve photo-gelation dynamics with high accuracy across length scales. Here, we employ photorheology to study the gelation of light-activated thermosetting polymers, enabling real-time tracking of viscoelastic changes under controlled illumination. This approach identifies key gelation signatures, including monotonic growth of the storage modulus and an overshoot in the loss modulus, which we attribute to the evolution of clusters and the transition from liquid-like to solid-like viscoelastic behavior. By monitoring the viscous-to-elastic transition, we aim to identify the gel point and characterize critical gelation dynamics. Linking these rheological observations to molecular-scale processes such as cluster formation and network connectivity establishes a multiscale framework connecting photoreaction kinetics to emergent material properties, advancing the design of photopolymerized materials.