Influence of Alkyl Length on the Morphology and Higher-Order Structure of Poly(amic acid) Flower-Like Particles

Flower-like particles (FLPs) are highly attractive for their versatile applications. However, there is no exclusive synthesis route or mechanism for the fabrication of polymeric FLPs. In this study, we investigated how alkyl chain length influences the morphology of semiaromatic poly(amic acid) (PAA) FLPs synthesized via one-step precipitation polymerization in the mixed solvent of cyclohexanone and acetone. Structurally analogous diamines with varied alkyl lengths (C4, C6, C8, and C12) were synthesized to polymerize with pyromellitic dianhydride (PMDA), designated as DA-n/PMDA (n = 4, 6, 8, 12). FLP size exhibited alkyl length dependence. Wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) analysis confirmed the existence of a higher-order structure of DA-n/PMDA particles. Hansen solubility parameters were calculated to quantitatively evaluate the interaction between DA-n/PMDA and the mixed solvents, revealing the flower-like morphology preferentially formed at the low solubility condition.