Morphology RegulationInduced by the IntramolecularCyclization Reaction of Poly(amic acid) to Form Uniform Nanoribbons

The structure and morphology of polymeric nanomaterials are key factors for their properties and potential applications, the precise regulation of which is the focus of the field of polymer self-assembly. In this study, an alternative strategy for morphology regulation through the intramolecular cyclization reaction of poly(amic acid) (PAA) is proposed. PAA is synthesized by the stepwise polymerization of 2,6-diaminoanthraquinone and pyromellitic dianhydride, which self-assembles into various unusual micrometer sized morphologies including networks composed of nanowires, helical ribbons, and branched helical ribbons depending on initial concentration. Upon thermal treatment, rigid polyimide (PI) segments are generated in the backbone of PAA, leading to the formation of poly(amic acid-<i>stat</i>-imide), and nanoribbons with a thickness of about 20 nm and precisely controlled width are obtained. The results demonstrate that the thermally induced imidization reaction at 160 and 180 °C significantly enhances the polymer chain rigidity, extends the conjugated segments in the main chain, and drives the formation of nanoribbons. Moreover, the fluorescence spectra exhibit a visible red shift with the increase of the annealing temperature, potentially arising from expansion of the conjugation structure by the generated PI segments due to the narrowing of the energy gap between the highest occupied molecular orbital and lowest unoccupied molecular orbital levels. This study highlights the critical role of intramolecular cyclization reactions in morphology evolution, offering an avenue for regulating the structure of nanostructures and achieving the controlled fabrication of nanoribbons.