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

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