Low-Wear Partially Fluorinated Polyimides

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Abstract
Tribological studies were conducted on five different polyimide solid bodies formulated from the diamine 2,2-bis [4-(4-aminophenoxy)phenyl] hexafluoropropane (4-BDAF) and the dianhydrides pyromellitic acid (PMDA) and benzophenonetetracarboxylic acid (BTDA). The following polyimides were evaluated 4-BDAF/PMDA, 4-BDAF/BTDA, 4-BDAF/80 mole percent PMDA, 20 mole percent BTDA, 4-BDAF/60 mole percent BTDA. Friction coefficients, polyimide wear rates, polyimide surface morphology, and transfer films were evaluated at sliding speeds of 0.31 to 11.6 m/s and at temperatures of 25° to 300°C. The results indicate that the tribological properties are highly dependent on the composition of the polyimide and on the experimental conditions. Two of the polyimides produced very low wear rates but very high friction coefficients (greater than 0.85) under ambient conditions. They offer considerable potential for high-traction applications such as brakes.