Resonant infrared pulsed laser deposition of a polyimide precursor

Poly(amic acid) (PAA), a precursor to polyimide, was successfully deposited on substrates without reaching curing temperature, by resonant infrared pulsed laser ablation. The PAA was prepared by dissolving pyromellitic dianhydride and 4, 4' oxidianiline in the polar solvent N-methyl pyrrolidinone (NMP). The PAA was deposited in droplet-like morphologies when ablation occurred in air, and in string-like moieties in the case of ablation in vacuum. In the as-deposited condition, the PAA was easily removed by washing with NMP; however, once cured thermally for thirty minutes, the PAA hardened, indicating the expected thermosetting property. Plume shadow-graphy showed very clear contrasts in the ablation mechanism between ablation of the solvent alone and the ablation of the PAA, even at low concentrations. A Wavelength dependence in plume velocity was also observed.