Living spontaneous gradient copolymers of acrylic acid and styrene: one-pot synthesis of pH-responsive amphiphiles

RAFT polymerization was used to prepare copolymers of acrylic acid (AA) and styrene (STY) with mole fractions of STY (F(STY)) ranging from 0.1 to 0.3 and targeted degrees of polymerization between 50 and 150. The high reactivity of AA-terminal radicals towards STY in this system (r(AA) = 0.082) resulted in the spontaneous formation of composition gradients, resulting in polymers with block-like structures comprising a STY-rich segment, a relatively short transitional segment, and a segment of AA homopolymer. Atomic force microscopy analysis of thin films of the copolymer revealed phase separated structures which developed after exposure to water. Dynamic light scattering measurements showed pH-responsive amphiphilicity that resulted in dissolved polymer at neutral and basic pH and self-assembly in weakly acidic solutions.