Synthesis of branched polymers by means of living anionic polymerization. 13. Synthesis of well-defined star-branched polymers via an iterative approach using living anionic polymers

We have developed a new iterative methodology for the synthesis of both regular and asymmetric star-branched polymers. The methodology involves only two sets of reactions for the entire iterative synthetic sequence: a living linking reaction of either 1,1-bis [3'-(1-phenylethenyl)phenyl] ethylene or 1,1-diphenylethylene (DPE) functionalized polymers with living anionic polymers and an in-situ reaction for introducing DPE moieties into the polymers. By repeating the two reactions in the iteration, a series of regular star-branched polystyrenes of A(3), A(6), A(9), A(12), and A(15) types and asymmetric star-branched polymers of A(3)B(3) and A(3)B(3)C(3) types were successfully synthesized. There does not seem to be a steric limitation even in the fifth iteration. The A and B segments in these star-branched polymers were polystyrene and poly(4-methoxystyrene), respectively, and the C segment was poly(4-tert-butyldimethylsilyloxystyrene), poly(4-trimethylsilylstyrene), or polyisoprene. Their arm segments were precisely controlled in chain length, with well-defined architectures, and high degrees of compositional homogeneity, as confirmed by H-1 NMR, SEC, VPO, SLS, and viscosity measurements.