Graft and dendronized polymers have attracted much attention in the polymer community, and there have been significant efforts to develop better synthetic methods. Herein, we report the highly efficient synthesis of graft and dendronized polymers by using Cu-catalyzed multicomponent polymerization (MCP). Based on diversity-oriented synthesis, we prepared a library of various graft and dendronized polymers from combinations of three types of monomers (mono-functionalized alkynes, bis-sulfonyl azides, and diamines/diols) that are bench stable and readily accessible. After reaction optimization, 54 samples of high-molecular-weight graft and dendronized polymers were prepared, the MCP method allowing simultaneous manipulation of the structures of both the main chains and the side chains. Moreover, because of the severe steric hindrance of the side chains, these polymers adopted extended conformations, as shown by the large shape parameter in solution. Also, the extended morphology of the single polymer chains was directly visualized by atomic force microscopy and transmission electron microscopy in the solid state. Most importantly, this diversity-oriented polymerization became possible because of highly step-economical and efficient one-step MCP, paving the way toward the easily tunable synthesis of graft and dendronized polymers.