<p>This study provides a comparative evaluation of epichlorohydrin-based elastomers, including poly(epichlorohydrin) (CO), poly(epichlorohydrin-co-ethylene oxide) (ECO), and poly(epichlorohydrin-co-ethylene oxide-co-allyl glycidyl ether) (GECO), with the goal of clarifying structure–property relationships driven by molecular architecture. These elastomers are commonly used in oil and fuel hoses, seals, gaskets, and automotive sealing applications that require low-temperature flexibility, thermal stability, and chemical resistance. The curing behaviour, mechanical properties, viscoelastic energy dissipation, crosslink density, and thermo-mechanical relaxation behaviour were systematically studied using simplified and consistent formulations. The results show that the addition of ethylene oxide and allyl glycidyl ether significantly affects curing rates, network structure, and relaxation characteristics. ECO cures faster and is stiffer, whereas CO exhibits better ductility and energy dissipation. Conversely, GECO demonstrates improved thermo-mechanical stability due to a higher extent of chemically effective crosslinks. Overall, these findings emphasise the importance of molecular architecture in customising the performance of epichlorohydrin-based elastomers and offer key insights for optimising elastomer design for specific industrial applications.</p>