Rigid, fused-ring molecules as nano-reinforcements for engineering polymers

Rigid, fused-ring molecules were investigated as nano-sized reinforcements for engineering polymers. Because of the high specific surface area associated with their small size, it was expected that they would provide greater enhancement of modulus than equally stiff reinforcements of millimeter and micron dimensions. The expected enhancement was not realized, a result attributed to the bulky alkyl substituents on the rings, placed there to make the fused-ring molecules soluble and dispersible at the molecular level in engineering polymers. It was concluded that the free volume introduced to the nanocomposites by these substituents counteracted the stiffening effect of the fused-ring structure in the molecules. The results point out the inherent trade-off with fused-ring molecules as reinforcements; the types of substituents required to make the molecules dispersible in a polymer matrix are also those that reduce its modulus.