Orientation of aromatic ion exchange diamines and the effect on melt viscosity and thermal stability of PMR-15/silicate nanocomposites

Nanocomposites of PMR-15 polyimide and a diamine modified silicate were prepared by the addition of the silicate to PMR-15 resin. The orientation of the ion exchange diamine within the silicate gallery was evaluated by x-ray diffraction and found to depend on the clay cation exchange capacity. The melt viscosity of the oligomer and the uncured nanocomposite was measured. The melt viscosity exhibited a dependence on the orientation of the diamine in the silicate interlayer and, in some cases, on the chain 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, a poorer nanocomposite thermal oxidative stability was also observed, compared to the less viscous systems. The melt viscosity was tailored by co-exchange of an aromatic diamine and an aliphatic amine, increasing the thermal oxidative stability of the nanocomposite. PMR-15/silicate nanocomposites were investigated as a matrix for carbon fabric reinforced composites. Dispersion of an organically modified silicate into the PMR-15 matrix greatly enhanced the thermal oxidative stability of the polymer matrix composite.