From this work, one can conclude that compositions which have excellent mechanical properties can be prepared by melt-mixing thermoplastic vulcanizates. (A thermoplastic vulcanizate is a composition containing vulcanized rubber particles dispersed in a thermoplastic. Such a composition is usually prepared by vulcanizing the rubber during its melt-mixing with a thermoplastic.) The excellent mixed TPV compositions can be obtained even though the rubbers and plastics are mutually grossly incompatible with respect to thermodynamic considerations. In such cases, however, it appears to be necessary that a compatibilizing agent be present in the mixture to promote the interaction between the thermoplastic materials. Block copolymers whose molecules contain blocks common to each of the thermoplastic blend components are good technological compatibilizing agents (e.g., polypropylene-nylon block copolymers to compatibilize mixtures containing polypropylene and nylon). Compatibilizing block copolymers can form in situ during melt mixing. This appears to be the case when one of the thermoplastic blend components is functionalized to chemically link with another thermoplastic component of the mixed TPV composition. The rubber associated with one thermoplastic can differ greatly from the rubber associated with another thermoplastic component of the mixed TPV blend. Thus, a composition which has good mechanical properties can contain both differing thermoplastics and differing rubbers. As a result, the possible combinations of components for TPV compositions has been greatly expanded.