Synthesis of Amphiphilic Poly(acrylic acid)‑<i>b</i>‑poly(<i>n</i>‑butyl acrylate-<i>co</i>-acrylic acid) Block Copolymers with Various Microstructures\nvia RAFT Polymerization in Water/Ethanol Heterogeneous Media

Abstract

The\nbatch copolymerization of <i>n</i>-butyl acrylate\n(50 mol %) and acrylic acid (50 mol %)two monomers with close\nreactivity but with very different water solubilitywas performed\nunder RAFT (reversible addition–fragmentation chain transfer)\ncontrol, in heterogeneous conditions in water or water/ethanol mixtures.\nThe polymerizations were conducted in the presence of poly­(acrylic\nacid) end-capped with a trithiocarbonate reactive group, serving as\na control agent, a precursor for the in situ synthesis of amphiphilic\nblock copolymers and a stabilizer for the formed particles. Good control\nover the polymerization and stable colloidal suspensions were achieved\nunder such conditions. The kinetic study demonstrated that the polymerization\nrates of each monomer varied upon a change of the water/ethanol volumetric\nratios and of the overall comonomer concentrations. The compositional\nmicrostructure of the copolymers was characterized by NMR analysis\nand by potentiometric titration. This work demonstrates that the distribution\nof the comonomer units in a copolymer formed under heterogeneous conditions\ncan be controlled by the solubility of the monomers in the medium,\nhence leading to various types of compositional gradient structures.