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

Abstract

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.