Summary: A macromonomer (1) consisting of a polystyrene chain and an acetylenic chain end ($\overline M _{\rm n}$ = 2 500, $\overline M _{\rm w} /\overline M _{\rm n}$ = 1.20) was prepared by atom transfer radical polymerization. Macromonomer 1 was copolymerized with phenylacetylene (2) and propargyl 2‐bromopropionate (3) by using Rh catalysts at varying feed ratios from 10 to 50 wt.‐% to produce graft copolymers 4 and 5, respectively. The synthesized copolymers 4 and 5 possessed a conjugated polyene main‐chain and polystyrene grafts, and contained 11–34 and 16–77 wt.‐% of polystyrene with $\overline M _{\rm n}$ of 61 400–144 000 and 19 300–22 500, respectively. Graft copolymer 4 was a yellow solid and thermally stable up to 225 °C, whereas 5 was a brown solid with weight loss beginning at 175 °C. Graft copolymers 4 and 5 exhibited UV‐vis absorption edges at 525 and 425 nm, respectively, which are attributable to the conjugated main‐chain structure.Copolymerization of the acetylene‐terminated polystyrene‐based macromonomer with monosubstituted acetylenes.magnified imageCopolymerization of the acetylene‐terminated polystyrene‐based macromonomer with monosubstituted acetylenes.