Synthesis and self-assembly of a pH-sensitive hyperbranched multiarm copolymer

Reversible addition-fragmentation transfer (RAFT) polymerizations of acrylic acid were conducted using fractionated hyperbranched polyester ( Bolton H20 ) based macroRAFT agent to obtain a hyperbranched multiarm copolymer of H20-star-PAA. Phase transition and self-assembly behavior of H20-star-PAA at different solution pH were also studied by using dynamic light scattering ( DLS ) and transmission electron microscopy ( TEM ) . The results show that at lower polymer concentrations, the hyperbranched macromolecules exist as unimolcular core-shell nanostructures with hydrophobic BoltornH20 as the core and swollen poly(acrylic acid) (PAA) as the shell, and the PAA shells will collapse on the surface of the micelles with decreasing the solution pH. While in high concentrations of the polymer, H20-star-PAA self-assemble into large multimolecular micelles due to the secondary aggregation of unimolecular micelles stabilized by the intermolecular hydrogen bonding.