Controlling morphological structures of polypyrrole tubes in oxidative polymerization of pyrrole-β-naphthalenesulfonic acid complexes

Abstract

The morphological structure of polypyrrole (PPy) tubes formed via oxidative polymerization of pyrrole (Py) with β-Naphthalenesulfonic acid (NSA) was examined. The study focuses on the 3:1 complex of Py and NSA in water, where subsequent polymerization is templated by the complex’s self-assembled structure. The complexes containing hydrophobic naphthyl groups and trimeric pyrrole units initially form spherical aggregates, which gradually transform into crystalline needles over time. Our observations indicate that the interval between mixing pyrrole (Py) with NSA and the addition of the oxidizing agent plays a decisive role in determining both the morphology and size of the resulting PPy tubes. When the oxidizing agent is introduced immediately after combining pyrrole and NSA, PPy nanotubes with diameters ranging from 80 to 200 nm are produced. Conversely, if the oxidizing agent is added after a certain period post-mixing, PPy tubes with diameters extending to several micrometers are obtained. Adding a small amount of 2,2′-binaphthyl phosphoric acid to the Py and NSA solution inhibits the crystallization into macroscopic needles, resulting in PPy nanotubes. The twisted binaphthyl structure disrupts parallel packing among NSA moieties, preventing crystallization. This work demonstrates that PPy tube morphology can be controlled by adjusting polymerization timing or using crystallization-disruptive dopants, providing an effective method for tuning conducting polymer tube size and morphology. © The Author(s), under exclusive licence to The Polymer Society of Korea 2026.