Kinetics of Network Re-Formation in Hydrolytic Degraded AFR700B Polyimide Resin

Abstract

Dynamic mechanical spectrometry was used to investigate the network formation processes during the high-temperature isothermal post-cure of virgin and hydrolytic degraded AFR700B resin. Upon exposure to hydrolytic conditions, a significant degradation in physical and mechanical properties of newly developed high-temperature PMR type polyimide resins (AFR700B) was observed. In this study we are particularly interested in the kinetics and the controlling mechanism of the network formation and re-formation processes at the high-temperature post-cure stage. In situ viscoelastic experiments were performed at a temperature of 400 °C. At this temperature the curing of polymer resin continues, thus the isochronal elastic modulus increases as the curing time increases. Furthermore, it was possible to perform a time–curing time superposition using these isothermal elastic modulus curves. This time–curing time shift-rate is then used as a direct measure of the kinetics of polyimide network formation. Interestingly, in this study we found that the time–curing time shift-rate for the hydrolytic degraded samples was identical to the time–curing time shift-factor of virgin ‘ascured’ formulated samples. This observation does not necessarily imply that the chemistry of polyimide network formation is the same, but instead that the controlling mechanism of network formation must be identical.