Precise synthesis of asymmetric star-shaped polymers by coupling reactions of new specially designed polymer anions with chain-end-functionalized polystyrenes with benzyl bromide moieties

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Abstract
We have developed a novel methodology using polymer anions specially designed to comprise either of the three same or different polymer segments for the synthesis of well-defined regular and asymmetric star-shaped polymers. The polymer anion was prepared by the addition reaction of living anionic polymer to in-chain-functionalized polymer with 1,1-diphenylethylene (DPE) moiety and in situ coupled with chain-end-functionalized polystyrene with two or four benzyl bromide moieties. Although the anions located at the cores of 3-armed star polymers were believed to be highly sterically hindered, the coupling reactions proceeded virtually quantitatively under the conditions in THF at −78 °C for 24 h. Regular 7-armed A7 and 13-armed A13 star-shaped polystyrenes as well as quite new asymmetric 7-armed A2B2C2D and 13-armed A4B4C4D star-shaped polymers were synthesized in ca. 100% yields. Four polymer segments, A, B, C, and D, were, poly(4-trimethylsilylstyrene), poly(4-methoxystyrene), poly(4-methylstyrene), and polystyrene prepared by sec-BuLi-initiated living anionic polymerization. Thus, three same or different polymer chains could be simultaneously introduced into either two or four benzyl bromide reaction sites only by one-step coupling reaction with the above-prepared polymer anion. The resulting star-shaped polymers all were well-defined in architecture and precisely controlled in-chain length and composition. Accordingly, they have a high molecular weight and structural homogeneity. Among them, asymmetric star-shaped polymers synthesized herein are the first successful examples comprised of four plural different polymer segments. As expected, new morphologies with nanoscopic ordered structures applicable to nanotechnology have been expressed.

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