A non-crystallization-driven strategy for the preparation of non-spherical polymeric nanoparticles.

To fabricate precisely defined non-spherical nanostructures like those widely exist in the biological domain by self-assembly of synthetic polymers without employing crystallization-driven forces is still a great challenge. In this study, we report a strategy to fabricate nanoparticles with advanced hierarchical architectures using styrene and methacrylic as monomers and maleamic acid-α-methyl styrene copolymer as a macroinitiator by polymerization-induced self-assembly (PISA). The structure of the prepared particles changed from common spherical micelles to cubes with edge lengths ranging from 50 to 200 nm when the solvent was 50 wt% ethanol in water and the monomer molar ratio of styrene to 2-hydroxyethyl methacrylate was 3:1. The growth of the cubic nanoparticles exhibited an interesting self-assembly process, initially forming vesicles with irregular cubes inside them. As the polymerization progressed, the inner cubes escaped from the vesicles and finally generated well-defined cubic nanoparticles. Wide-angle X-ray scattering (WAXS) results of the cubic nanoparticles indicated that no crystalline structure existed. The formation mechanism of the cubic nanoparticles was elucidated via density functional theory (DFT) calculations. This strategy was further applied to various monomers, and its universality was confirmed by successful fabrication of different non-spherical nanoparticles such as rectangles, fusiform platelets, and triangular pyramids.