Ring-opening metathesis polymerization (ROMP) is a great tool for synthesizing polyolefin materials with different topologies, including hyperbranched polymers—polymers with high degrees of branching and many end groups. However, hyperbranched polymer synthesis via ROMP is challenging due to multifunctional-monomer or multi-polymerization requirements. To simplify the synthesis of hyperbranched ROMP polymers, we developed a new synthetic approach: Self-condensing ROMP. The self-condensing ROMP approach involves a ROMP initiator modification to attach a ROMP-polymerizable group (a ROMP monomer), producing a ROMP "inimer" (initiator + monomer). The ROMP inimer initiates the polymerization and becomes a branching unit in the polymer structure, resulting in single-step hyperbranched polymer synthesis. The key challenge is controlling of this approach the ROMP initiator reactivity to avoid initiating polymerization during the ROMP inimer synthesis. Well-defined ruthenium-based olefin metathesis catalysts are common ROMP initiators due to their high stability, reactivity, and functional group tolerance. Thus, we studied the olefin metathesis catalyst activation temperature to enable ROMP initiator-monomer coupling. Based on the catalyst activity, we designed and synthesized a series of ROMP inimers. Then, we synthesized hyperbranched polymers via self-condensing ROMP. The characterization of hyperbranched polymers indicated the effect of branching density on the physical properties of the polymer. This approach introduced a new class of olefin metathesis complexes, ROMP inimers, containing both the initiator and propagating center. This approach provides a way to synthesize hyperbranched polymers from any known ROMP monomers in a single step. This dissertation also includes the synthesis and characterization of a bimetallic Ru complex that could directly synthesize cyclic polyolefin. We also include the synthesis and characterization of copper-ruthenium bimetallic olefin metathesis catalysts. / Doctor of Philosophy / Hyperbranched polymers are a class of polymers having highly branching structures and functional end-groups, and presenting distinct physical and chemical properties compared with linear polymers. Hyperbranched polymers have been used for many applications including processing additives, cross-linkers, compatibilizers, and catalyst supports. Well-defined ruthenium-based olefin metathesis catalysts enable the synthesis of materials with different topologies, functionalities, and chemical and physical properties via ring-opining metathesis polymerization (ROMP). Ligand modifications on ruthenium catalysts have been applied to improve the catalyst stability and reactivity. However, this dissertation modifies olefin metathesis catalysts to synthesize hyperbranched polymers in a single step. This dissertation illustrates catalyst functionalization with a ROMP monomer moiety to synthesize a ROMP inimer (inimer= initiator + monomer). The ROMP initiator—olefin metathesis catalyst—and ROMP monomer coupling produces an "inimer". The inimer can undergo self-condensing ROMP with a ROMP monomer addition to synthesize hyperbranched polymers. This approach introduced a new class of olefin metathesis complexes containing both the initiator and propagating center. This approach also provides a way to synthesize hyperbranched polymers from any known ROMP monomers in a single step.