Transferable shadow cure: A new approach to achieving cationic photopolymerization in light‐restricted areas

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Abstract
Transferable shadow cure is presented as an improved method of shadow cure. In this new method, active centers are formed in one space, and active‐center‐containing monomer is then moved to another space where the bulk of the polymerization proceeds. This transference enables inclusion of pigments and fillers, layering in thick systems, and polymerization in complex geometries. Kinetic analysis of shadow‐cure samples shows conversions consistently ~15% less than comparable light‐cure samples. In addition, shadow‐cure films have a higher Tg and crosslink density than light‐cure films, likely driven by annealing that occurs during the first dynamic mechanical analyzer temperature ramp sequence. A central‐composite design explored the effect of sample depth, effective irradiance, exposure area, and exposure time on conversion and the weight percent of the light‐cure section. The model predicts both responses are maximized by increasing effective irradiance and exposure time and decreasing sample depth, which is consistent with classical photopolymerization kinetics.

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