Orientation of Aromatic Ion Exchange Diamines and the Effect on Melt Viscosity and Thermal Stability of PMR-15/ Silicate Nanocomposites

Abstract

Nanocomposites of PMR-15 polyimide and a diamine modified silicate were prepared by addition of the silicate to the PMR-15 resin. The orientation of the ion exchange diamine within the silicate gallery was determined by x-ray diffraction and found to depend on the clay cation exchange capacity. The oligomer melt viscosity exhibited a dependence on the orientation of the diamine in the silicate interlayer, and in some cases, on the length of the diamine. A correlation was observed between the oligomer melt viscosity and the crosslinking enthalpy, where nanocomposites with an increased melt viscosity exhibited a decrease in enthalpy on crosslinking. After crosslinking, those nanocomposites with a high melt viscosity had poorer thermal oxidative stability compared to the less viscous systems. The melt viscosity was tailored by co-exchange of an aromatic diamine and an aliphatic amine into the silicate. Nanocomposites prepared with this silicate exhibited an increase in thermal oxidative stability compared to the neat resin.