The pH-responsive amphiphilic A(2)B(2) miktoarm star block copolymer., poly(acrylic acid)(2)-poly(vinyl acetate)(2) [(PAA)(2)(PVAc)(2)], With controlled molecular weight and well-defined structure was successfully synthesized via combination of single-electron transfer-mediated living radical polymerization (SET-LRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization methods. First, the precursor two-armed poly(t-butyl acrylate) (PtBA)(2) functionalized with two xanthate groups was prepared by SET-LRP of t-butyl acrylate in acetone at 25 degrees C using the novel tetrafunctional bromoxanthate (Xanthate(2)-Br-2) as an Imferter (initiator-transfer agent-terminator) agent. The polymerization behavior showed typical LRP natures by the first-order polymerization kinetics and the linear dependence of molecular weight of the polymer on the monomer conversion. Second, the A(2)B(2) miktoarm star block copolymer (PtBA)(2)(PVAc)(2) was prepared by RAFT polymerization of VAc using (PtBA-N-3)(2)(Xanthate)(2) obtained as the macro-RAFT agent Finally, the pH-sensitive A(2)B(2) amphiphilic miktoarm star block copolymer poly(acrylic acid)(2)-poly(vinyl acetate)(2) ((PAA)(2)(PVAc)(2)) was obtained by selectively cleavage of t-butyl esters of (PtBA)(2)(PVAc)(2). All the miktoarm star block copolymers were characterized by GPC, H-1-NMR, and FT-IR spectra The self-assembly behaviors of the amphiphilic A(2)B(2), miktoarm block copolymers (PAA)(2)(PVAc)(2) were also investigated by transmission electron microscopy. (C) 2009 Wiley Periodicals. Inc J Polym Sci Part A: Polym Chem 47: 6908-6918, 2009