Ultra‐fast polymerization of epoxy‐acrylate resins by pulsed laser irradiation

The 337.1‐nm emission of a pulsed nitrogen laser was shown to initiate the crosslinking polymerization of epoxy‐acrylate photoresists effectively. We evaluated the extent of curing from the amount of insoluble polymer formed and by the decrease in infrared (IR) absorption of the reactive double bond at 810 cm−1. With the large power density available in the laser pulse (0.5 MW cm−2) rates of polymerization as high as 108 mol L−1 s−1 were observed in the presence of air. Quantum yield measurements indicated that each photon absorbed can create as many as 450 crosslinks; the kinetic chain length was calculated as ca. 4000 double bonds polymerized per initiating radical. During the induction period due to oxygen inhibition each photoinitiator radical consumed 1 O2 molecule. The influence of the monomer and photoinitiator used on the sensitivity of the resin was examined; the best performing formulation contained the epoxy‐acrylate oligomer, pentaerythritol triacrylate, as monomer and 2,2 dimethoxy‐2‐phenyl‐acetophenone as photoiniatior. All the formulations studied can be cured by a single 500‐kW laser pulse of 8 ns duration, provided that the irradiation is carried out in an inert atmosphere or with a focused laser beam.