Spatial and temporal evolution of the photo initiation rate for thick polymer systems illuminated on both sides

Abstract

Photopolymerizations of thick systems are inherently non-uniform and much more complex than polymerizations of films and coatings. This contribution presents a mathematical description of the evolution of the photoinitiation rate profile for a thick photopolymerization system illuminated on two sides. Simulation results revealed that when two lamps of equal intensity are used, the spatial and temporal evolution of the photoinitiation rate profile follows a characteristic progression from a bimodal distribution to a unimodal shape with a maximum in the center of the sample. The addition of a second light source can lead to an initiation profile that is more uniform throughout the sample. System variables such as the initiator concentration, molar absorptivity and monomer absorptivity determine how the photoinitiation rate profile evolves. For example, increasing initiator concentration results in sharper initiation fronts which move through the sample more slowly. A reflective boundary condition, a special case of two-sided illumination using only one lamp, was found to enhance the initiation rate and uniformity for some reaction systems. This model provides the fundamental understanding needed to ensure proper selection of reaction components for effective photoinitiation in thick systems, including the possibility of a second light source as an additional design variable. © 2005 Society of Chemical Industry.