Expanding the Scope of Self-Assembly: Heat-Induced Self-Assembly of Block Copolymers with High Solids

Polymerization-induced self-assembly (PISA) has gained widespread recognition as a potent tool for accessing nano-objects with diverse morphologies. To facilitate its practical application, further development of the self-assembly method is still urgent and challenging. We herein report an innovative self-assembly approach termed heat-induced self-assembly (HISA), enabling the preparation of nano-objects with abundant morphologies by direct thermal dissolution of solid block copolymers (BCPs) in selective solvents at elevated concentration (20% w/w). The BCPs of polyisoprene-b-polystyrene (PI-b-PS), polyisoprene-b-poly(methyl methacrylate) (PI-b-PMMA), and polyisoprene-b-poly(4-vinylpyridine) (PI-b-P4VP) were prepared by living anionic polymerization (LAP) for HISA investigation. Furthermore, this methodology was extended to heat-induced cooperative assembly (HICA) comprising PI-b-PSm/PSn (ABm/Bn) and PI-b-PSm/PI-b-PSn (ABm/ABn), where B represented the PS core-forming block. The feasibility of HISA and HICA processes was investigated, and a library of morphologies, including spheres, worms, vesicles, nanotubes, and sponges, were collected. The pseudophase diagrams were constructed for both ABm/Bn and ABm/ABn systems to provide guiding principles for the tailored morphologies. To evaluate the universality of HISA and HICA techniques, the ACm/Cn and ABm/ACn systems (C represented PMMA or P4VP core-forming block) were further investigated. The corresponding glass transition temperatures (Tgs) of BCPs in both dry and solvated states were analyzed to gain further insights into the HISA and HICA techniques. These high-concentration assembly strategies including HISA and HICA combined operational simplicity with morphological diversity, showing significant potential in practical applications.