We demonstrate that ring-opening metathesis copolymerization of 3-hexyl-cis-cyclooctene and cis-cyclooctene in the presence of maleic acid as a chain transfer agent leads to precise control over the molar mass, branching and crystallinity of the resulting carboxy-telechelic polyalkenamers. Subsequent hydrogenation using a silica-supported platinum catalyst had a negligible effect on the carboxy functionality and led to telechelic polyolefins with high thermal resistance, low glass transition temperatures (<-57 C), little to no crystallinity, and viscosities similar to those of liquid silicon rubber prior to cross-linking. These properties are ideal for easily processable reactive polyolefin prepolymers that can be readily cured to form elastomers. We demonstrate that a fast and controlled curing process can be achieved in the presence of polyfunctional aziridines. The properties of the thermoset elastomer products were evaluated by tensile, differential scanning calorimetry, and dynamic mechanical analyses.