Crosslinking characterization of a polyimide: AFR700B

摘要

Crosslinking in AFR700B polyimide was studied using several techniques. Crosslinking could not be detected using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Swelling in n-methyl pyrroli done [NMP) showed network formation occurs at cure temperatures greater than or equal to 325 degrees C (617 degrees F), but the reaction kinetics could not be determined from the data. Dynamic mechanical analysis [DMA] studies have shown that the storage modulus (G') increased with increasing cure temperature up to 350 degrees C (662 degrees F), and was constant above 350 degrees C (662 degrees F), indicating that crosslinking via the reverse Diels-Alder reaction was occurring. A broad secondary transition was seen in the loss modulus (G '') curves, centered between 150 and 180 degrees C (302 and 356 degrees F). This secondary transition appeared at a cure temperature of 300 degrees C (572 degrees F) and became more dominant with increasing temperature and time. This secondary transition was not seen for cures <300 degrees C (572 degrees F) when the chains have not crosslinked. Therefore, this is likely due to a crosslink bond rather than one in the backbone. At 1 atm, crosslinking followed second-order kinetics based on the increase in glass transition temperature (T-g). The Arrhenius plot of the rate constant showed a break in the slope, possibly indicating a change in reaction mechanism. At 1.38 MPa (200 psi), the T-g data was too scattered to determine the kinetics.