Patterned polymer manufacturing by laser-ignited multi-initiation-point frontal polymerization*

We present laser-patterned photothermal heating as a new means to simultaneously initiate self-propagating polymerization reactions at multiple locations in a 2-D sample. While frontal polymerization (FP) is well established for rapid polymerization of thermoset plastics using only a small point input of heat rather than a kiln, until now FP initiated at more than two points simultaneously has not been demonstrated. We incorporated carbon black (CB) particles into liquid resin (dicyclopentadiene; DCPD) to enhance absorption of energy from a rapidly scanned Ti:Sapph laser (800nm) focused on a shallow and broad sample (3 mm x 10 cm; d x w). We demonstrate successful multipoint polymerization at up to seven sites and in various geometries and show that initiation in DCPD+CB requires an approximately fixed energy input at high powers where thermal diffusion can be neglected. We also present a theoretical framework for predicting the seam patterns formed by the collision of multiple fronts, and an inverse solution for determining the initiation points required to form a desired material pattern. Future applications of this approach could be used for rapid, energy-efficient manufacturing of novel patterned materials with composite-like properties.