Well‐defined five‐arm star polymers, having different arms in molecular weight or composition, were synthesized by linking reactions of end‐functionalized polystyrenes with two chloromethylphenyl (CMP) groups and polymer anions consisting of two identical or different polymer chains. The polymer anions were prepared by coupling living anionic polymers of styrene or isoprene with 1,1‐diphenylethylene (DPE)‐end‐functionalized polymers. They were then reacted in situ with the CMP‐end‐functionalized polystyrenes to afford heteroarm star polymers of the AA′2A″2, AA′2B2, and AB2C2 types where the A, B, and C segments were polystyrene, poly(a‐methylstyrene), and polyisoprene, respectively. 1H NMR spectroscopy, SEC, vapor pressure osmometry (VPO), and static light scattering measurements evaluated the well‐defined architecture of these polymers.

The synthesis of well-defined three-and five-arm star polymers, with varying arm lengths, was described by the method based on anionic living polymerization. A three-arm AB 2 star polymer was synthesized by the linking reaction of a specially designed two chloromethylphenyl-end-functionalized polystyrene prepolymer with the anionic living polymer of t-butyl methacrylate initiated with diphenylmethylpotassium. A five-arm AA' 2 B 2 star polymer was synthesized by the linking reaction of the same functionalized polystyrene having two chloromethylphenyl termini with the block copolymeric anion prepared from the coupling reaction of polystyryllithium with 1,1-diphenylethylene-end-functionalized poly(a-methylstyrene). Both star polymers were obtained in more than 95% yields and were found to possess well-defined structures in terms of molecular weight, molecular weight distribution, arm number, and composition.