Development of a two‐stage,dual‐Arrhenius rheology model for a high‐performance phenylethynyl‐terminated poly(etherimide)

A two‐stage, dual‐Arrhenius rheology model was successfully utilized to model the isothermal complex viscosity of a phenylethynyl‐terminated poly(etherimide) as a function of time and temperature over the experimental temperature range of 325°C to 350°C. Union of the dual‐Arrhenius model with a previously developed combination reaction kinetics model provided a chemoviscosity model giving viscosity as a function of degree of cure. A two‐stage, versus a single, dual‐Arrhenius model was used to accommodate a transition in the reaction process from chain growth to branching and network forming that was found to onset around a degree of cure of 0.37. The reduction in chain mobility brought on by branching and networking was quantified by the almost order of magnitude increase in the apparent activation energy for initial viscosity from the chain growth stage to the networking stage. The calculated apparent activation energies for gelation for the first and second stages, 2.14 × 10⁵ J/mol and 2.05 × 10⁵ J/mol, respectively, agree well with results presented elsewhere from differential scanning calorimetry measurements. The experimental procedures followed to obtain the rheological data and the construction of the model from these data are described; the predictions of the model are compared with experimental results.