Physical and Chemical Aging Effects in PMR-15 Neat Resin

摘要

The objective of this study was to determine whether a shifting approach can be used to account for both chemical and physical effects during long-term aging of high temperature polyimide thermoset polymers, such as the commercial material PMR-15. Stress relaxation curves measured after aging at 316 deg C for times up to 800 h could be shifted to form a master curve. The horizontal shift factors were found to increase with increasing aging time, consistent with a reduction in molecular mobility that occurs as a result of either physical aging or increased cross-linking. There was a correlation between the vertical shift factors and cure related chemical changes that cause T_g to increase and mass to decrease. Aging effects were partially reversed by heating the aged specimen above its glass transition temperature, indicating that a large portion of the aging is physical in nature. Specimens aged in nitrogen had a larger reversible component than specimens aged in air.