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In-situ composites based on self-reinforcing blends of engineering thermoplastics and thermotropic liquid crystalline polymers (TLCPs) are recently developed, innovative polymeric materials, which have been reported to exhibit outstanding property profiles. These profiles include superior mechanical properties, excellent thermal and dimensional stabilities at high temperatures, and improved melt processabilities. Such characteristics make in-situ composites very attractive as performance polymer-based materials for tribological applications. To date, a thorough investigation of the tribology of in-situ composites has not yet been undertaken and, thus, the potential of these composites as performance tribomaterials has not been effectively assessed. The present research addresses this issue. An investigation is carried into the elevated temperature tribology of in-situ composite systems based on binary blends of Polyetheretherketone (PEEK) and HX-1000, a commercially available TLCP, as well as on ternary blends of PEEK, Polyetherimide (PEI) and HX -1000. The specific tribological phenomenon investigated is unlubricated sliding. Friction and wear measurements are performed at selected temperatures in the range from 20°C to 250 °C using a pin-on-disk tribometer. Dynamic mechanical thermal analysis and morphological studies are carried out in conjunction with the tribological evaluation. The impact of operating temperature on tribological performance as well as active friction and wear mechanisms are discussed in terms of thermally activated molecular relaxation processes and the solid state morphology of the composite systems investigated. Basic knowledge of the way in which the structure, mechanical properties and tribological behavior of in-situ composites are interrelated is gained. Results from this research point to the validity of the concept of TLCP in-situ reinforcement as a means to produce thermoplastic-based performance tribomaterials. Ph. D.