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

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Abstract
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 coexchange 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.