EPRI of Distributions of Free Radicals in Polyimide Samples

A report describes experiments in which electron paramagnetic resonance imaging (EPRI) was used to determine one-dimensional spatial distributions of free radicals in two plate specimens of PMR-15 polyimide. One specimen had been postcured at a temperature of 315 °C in nitrogen, then thermally cycled 300 times between room temperature and 335 °C in air; the other specimen had been post-cured at 316 °C in air, then further postcured at 371°C in nitrogen, but not thermally cycled. EPRI of the thermally cycled specimen showed a higher concentration of free radicals in the surface layers than in the bulk.