We report the ring-opening metathesis reactivities of a series of unsymmetrically 1,1-disubstituted 1-methylcyclopropenes (CPEs). 1-Methyl-1-carboxylate CPEs underwent highly selective single addition to the Grubbs catalyst, enabling exclusive and complete chain-end functionalization of living polynorbornene (PNBE). In contrast, 1-methyl-1-carboxymethyl CPEs bearing an ester or carbonate underwent living polymerization to produce functionalizable homopolymers with controlled molecular weights, low dispersities, and low glass transition temperatures. Controlled ROMP of 1-methyl CPEs was exploited to synthesize new block copolymers (BCPs) composed of a rubbery PCPE homopolymer block and a glassy PNBE or PTD (TD = endo-tricyclo[4.2.2.0]-deca-3,9-diene) block or a CPE/cyclohexene-based alternating block, These results underscore the versatility of CPEs as a new class of monomers for ROMP, opening new doors to structurally diverse polymers beyond the predominant PNBE backbones.