Quasi-Monodisperse Crystalline Hexagonal Nanosheets from the Rapid Intramolecular Cyclization-Induced Self-Assembly of an Amorphous Poly(amic acid) at a Solid Content of 15%

Two-dimensional crystalline polymer nanosheets exhibit significant application potential across diverse fields due to their highly ordered structure and unique electrical, thermal, and mechanical properties. However, the facile preparation of crystalline polymer nanosheets at a high solid content still remains challenging, owing to the inherent complexity and kinetic characteristics of polymer crystallization. Herein, a robust intramolecular cyclization-induced self-assembly (ICISA) strategy is proposed to prepare uniform quasi-monodisperse crystalline hexagonal nanosheets at a high solid content of 15%. Upon thermal treatment of the PAA solution, insoluble and crystalline polyimide segments are generated at the main chain of the polymer, leading to the fast amorphous to crystalline transition and self-assembly of the polymer simultaneously within 10 min at gram scale. At low concentrations, ultrathin nanosheets with a feature thickness of 4.8 nm are formed, which overlap and stack to form thick nanosheets and eventually hexagonal nanosheets at high concentrations. The influence of annealing temperature on the degree of imidization, crystallinity, and morphology of the assemblies is investigated, confirming the optimal annealing temperature of 160 °C, ensuring the match between the rate of amorphous to crystalline transition and self-assembly. Overall, quasi-monodisperse crystalline hexagonal sheets are facilely prepared at a high solid content of 15% by the rapid ICISA strategy, overcoming the restriction of the slow kinetics of polymer crystallization during self-assembly.