The precise synthesis of a new series of densely grafted bottlebrushes that bear helical polyisocyanide side chains on polyisocyanide backbones is described. New Cl polymers, polyisocyanides that bear active pentafluorophenol ester pendants, were first prepared and then installed with a Pd(II) catalyst on each backbone carbon via transesterification. All the Pd(II)-catalyst pendants could efficiently catalyze the living polymerization of isocyanide monomers, leading to the formation of densely grafted bottlebrush polymers. The grafting density could be facilely tuned through changing the content of Pd(II) pendants on the backbone. Because both the backbone and the side chain were synthesized via living chain-growth polymerizations, a variety of bottlebrush polymers and core-shell bottlebrushes with different compositions and controlled structures were prepared. The new synthetic bottlebrush polymers showed distinctively enhanced viscosity and modulus which could be further regulated via varying the grafting density.