Dual Thermo- and pH-Responsive N-Cyanomethylacrylamide-Based Nano-Objects Prepared by RAFT-Mediated Aqueous Polymerization-Induced Self-Assembly

International audience; We report the straightforward synthesis of dual stimuli-responsive nano-objects using a RAFT-mediated polymerization-induced self-assembly (PISA) process in water. The key to complex and tunable responsiveness was the copolymerization of N-cyanomethylacrylamide, providing UCST-type polymers, with a pH-sensitive monomer (acrylic acid, AA). Not only the core block length, but also the acrylic acid content and slight changes in the degree of ionization of AA (αAA,0) in the polymerization medium had a great impact on the particle morphology. Generally, higher AA contents favored the formation of spherical nano-objects, while low αAA,0 led to higher order morphologies. We demonstrated that the nano-objects exhibited a complex dual responsiveness to changes in the degree of ionization and temperature. Progressively increasing post-polymerization the degree of ionization of the AA units incorporated in the copolymer (αAA) triggered morphological transitions. Remarkably, a single copolymer composition formed well-defined vesicles, worms, and spheres that eventually dissociated into individual chains. Temperature-dependent SAXS analyses evidenced a complex thermo-responsive behavior, which depended on the copolymer composition and αAA. For some compositions, we observed both a cloud and a clearing point, attributed to the formation of secondary aggregates and chain dissolution, respectively.