Successive Synthesis of Well-Defined Asymmetric Star-Branched Polymers up to Seven-Arm, Seven-Component ABCDEFG Type by an Iterative Methodology Based on Living Anionic Polymerization

The successive synthesis of asymmetric star-branched polymers with chemically different arms by the iterative methodology in which a 1,3-butadiene (Bd) functionality is utilized as a reaction site at each stage of the iteration, is described. The methodology involves only two sets of the following reaction conditions for the entire iterative synthetic sequence: (a) linking reaction of a living anionic polymer with the Bd functionality preintroduced into polymer and (b) reintroduction of the Bd functionality by reacting 4-methylene-5-hexenyl bromide with the Bd-derived anion in situ generated by the linking reaction. By repeating the two reaction sequence five times, a series of two-arm AB diblock, three-arm ABC, four-arm ABCD, five-arm ABCDE, followed by six-arm ABCDEF star-branched polymers were successively synthesized. In these polymers, the A, B, C, D, E, and F segments correspond to polystyrene, poly(α-methylstyrene), poly(4-methylstyrene), poly(4-methoxystyrene), poly(4-trimethylsilylstyrene), and poly(4- tert -butyldimethylsilyloxystyrene) convertible to poly(4-vinylphenol), respectively. The resulting polymers all were well-defined in star-branched architecture and precisely controlled in chain length as confirmed by the characterization results with SEC, 1 H NMR, and RALLS. A seven-arm ABCDEFG asymmetric star-branched polymer was synthesized by using the intermediate six-arm ABCDEF star-branched polymer anion as a macroinitiator to anionically polymerize 2-vinylpyridine to make the seventh arm. The resulting asymmetric star-branched polymer is quite new and composed of chemically different seven arms including acidic poly(4-vinylphenol) and basic poly(2-vinylpyridine) segments.