A novel high purity dual‐functional epoxy monomer, diglycidyl ether of 4,4′‐diallyl‐bisphenol‐A, is deliberately designed for the construction of a fishbone‐shaped heterochain polymer by polymerizing it with the methyl phenyl polysiloxane. Their curing reactions with Jeffamine D230 are investigated. The cured fishbone‐shaped heterochain polymer presents a wide transition range spanning over 120 °C with a peak half‐width of 62 °C. In contrast to the traditional epoxy/polysiloxane materials, the cured fishbone‐shaped heterochain polymer takes full advantage of the cooperative effect of epoxy and polysiloxane exhibiting excellent damping properties (tan δ > 0.3) at temperatures near the T g of the polysiloxane. This outstanding low‐temperature damping performance can be ascribed to the fishbone‐shaped structure of the heterochain polymer. These results provide new approach to explore high damping materials used at extremely low temperature (−125 °C). image