Crystalline\nNanoflowers Derived from the Intramolecular\nCyclization-Induced Self-Assembly of an Amorphous Poly(amic acid)\nat High Solid Content

The investigation of the amorphous\nto crystalline transformation\nand the corresponding influence on the self-assembly behavior of amphiphilic\npolymers are of significant interest in this field. Herein, we propose\nthe concept of intramolecular cyclization-induced self-assembly (ICISA)\nto prepare crystalline nanoflowers at a high solid content of 15%\non the basis of the amorphous to crystalline transformation of poly(amic\nacid) (PAA). Taking advantage of the reactive property of the PAA,\nrigid and crystalline polyimide (PI) segments are introduced to the\nbackbone of the PAA to give P(AA-<i>stat</i>-I) induced\nby the intramolecular cyclization reaction upon thermal treatment,\nleading to the in situ formation of crystalline nanoflowers. Revealing\nthe formation mechanism of the nanoflowers, we found that the nanosheets\nare formed at the early stage and then stacked to form the nanoflowers\nat high concentrations. The relationship between the degree of imidization\nand incubation temperature is quantitatively analyzed, and the effects\nof temperature on the morphology, degree of imidization, and crystallinity\nof the assemblies are also investigated. Furthermore, computer simulations\ndemonstrate the optimized temperature of ICISA of 160 °C, which\nensures the match between the intramolecular cyclization reaction\nrate, the self-assembly process, and the lowest energy state of the\nself-assembly system, resulting in the formation of nanoflowers with\nhigh crystallinity. Overall, a facile one-step strategy is proposed\nto prepare crystalline nanoflowers based on the in situ thermally\ntriggered intramolecular cyclization reaction of a PAA, which may\nbring fresh insights into the dynamic amorphous to the crystalline\ntransformation of polymers.