Self-assembly of single-chain nanoparticles from block copolymers into inverse bicontinuous structures

Polymer particles with inverse bicontinuous structures are widely used due to their well-defined ordered porous networks. These structures are typically prepared by the traditional self-assembly of amphiphilic block copolymers (BCPs) in solution or polymerization-induced self-assembly (PISA). In both methods, BCPs must be highly asymmetric with long hydrophobic chains. In this study, we report a credible approach where single-chain nanoparticles (SCNPs) preferentially self-assemble into inverse bicontinuous structures by folding the hydrophilic chains of BCPs, which can reduce the molecular area a0 and thus increase the packing parameter (P) to greater than unity. It is anticipated that this strategy will lessen the rigorous requirement of inverse bicontinuous structures on the BCP asymmetry. To illustrate this strategy, we prepared tadpole-like SCNPs of poly(4-vinylpyridine)-block-polystyrene (P4VP-b-PS) by intrachain cross-linking the P4VP blocks. Polymer cubosomes could be self-assembled from both linear BCPs and tadpole-like SCNPs, resulting in a distinct reduction in the minimal volume fractions of PS (fPS) (94.4% and 91.1%, respectively). A plausible formation mechanism for cubosomes was proposed. In addition, the efficiency of intrachain cross-linking and the property of the co-solvent played crucial roles in the formation of cubosomes. Overall, this work provides an effective method for preparing polymer particles with inverse bicontinuous structures from relatively low-asymmetric BCPs with a broad window. Single-chain nanoparticles preferentially self-assemble into cubosomes with a broad window by intrachain cross-linking the hydrophilic chains of block copolymers, which accounts for the smaller a0 and the larger P.