DSC ANALYSIS OF ELECTRON-BEAM IRRADIATED LARC-CPI

This work illustrates the response of LARC-CPI (a crystallizable polyimide) to electron-beam radiation exposure under a nitrogen-purged atmosphere. The response of LARC-CPI was monitored exclusively by differential scanning calorimetry (DSC), although some limited X-ray scattering experiments were also employed. Three different types of LARC-CPI samples were irradiated: the "as-received" semicrystalline films, highly amorphous films that were quenched from the melt, and recrystallized films. Comparison of the DSC behavior of these specimens elucidated the effects of electron-beam irradiation on LARC-CPI as well as the influence-of morphology (i.e., semicrystalline vs. amorphous states) on the radiation response of this polyimide. Results indicate that for the former two samples electron-beam radiation does not significantly alter the crystalline phase present during irradiation. However, upon subsequent heating and cooling, the level of crystallinity decreases in all samples exposed to high doses (in excess of 100 Mrad). In addition, the crystallization temperature increases substantially with increasing radiation dosage, while a slight increase in the glass transition temperature is also observed. These results suggest that cross-linking reactions may be occurring at sufficiently high doses, which would account for the observed melting and recrystallization behavior. However, due to the effects of thermal history on the crystallization behavior, there is some difficulty in definitively discerning all the specific effects of morphology on the radiation response of LARC-CPI.