Self-assembly of semiaromatic poly(amic acid) into flower-like microparticles via one-step precipitation polymerization

Flower-like particles (FLPs) are highly attractive materials owing to their intricate morphologies and high specific surface areas. However, a definitive method for fabricating organic FLPs with unique three-dimensional morphologies has yet to be established. In this paper, we report on a synthetic route for poly(amic acid) (PAA) FLPs using a specially designed semiaromatic PAA consisting of alternate rigid aromatic segments and flexible alkyl segments via one-step precipitation polymerization at room temperature. The particle morphology can be tuned from spherical to flower-like by adjusting the mixed-solvent ratio. Based on small-angle X-ray scattering, wide-angle X-ray diffraction, and polarized optical microscopy analyses, the flower-like morphology is attributed to the microcrystalline structure formed by the folded and stacked alignment of the PAA precursors. Moreover, solubility plays a crucial role in determining the crystallization rate and growth mechanism, thereby leading to variations in the flower-like morphology. Notably, the flower-like morphology is preserved after thermal imidization and carbonization. The as-synthesized carbon flowers demonstrated high catalytic activity and selectivity for the 2-electron electrochemical reduction of oxygen in an acidic electrolyte, which could be attributed to the N-content of 2.72% and the efficient mass transport granted by the open structure of the unique flower-like morphology.