Depolymerization breaks down polymer chains into monomers like unthreading beads, attracting more attention from a sustainability standpoint. When polymerization reaches equilibrium, polymerization and depolymerization can reversibly proceed by decreasing and increasing the temperature. Here, we demonstrate that such dynamic control of a growing polymer chain in a selective solvent can spontaneously modulate the self-assembly of block copolymer micellar nano-objects. Compared to polymerization-induced self-assembly (PISA), where irreversible growth of a solvophobic polymer block from the end of a solvophilic polymer causes micellization, polymerization/depolymerization-induced self-assembly presented in this study allows us to reversibly regulate the packing parameter of the forming block copolymer and thus induce reversible morphological transitions of the nano-objects by temperature swing. Under the coupled equilibria of polymerization with self-assembly, we found that demixing of the growing polymer block in a more selective solvent entropically facilitates depolymerization at a substantially lower temperature. Taking ring-opening polymerization of δ-valerolactone initiated from the hydroxyl-terminated poly(ethylene oxide) as a model system, we show that polymerization/depolymerization/repolymerization leads to reversible morphological transitions, such as rod–sphere–rod and fiber–rod–fiber, during the heating and cooling cycle and accompanied by changes in macroscopic properties such as viscosity, suggesting their potential as dynamic soft materials.

Supramolecular polymerization offers a fascinating opportunity to develop dynamic soft materials by associating monomeric building blocks via noncovalent interactions. We report that polymerization can spontaneously drive the supramolecular polymerization of nanoscale micellar objects. We constructed the patchy micelles via two-step polymerization-induced self-assembly. A horizontal association between the patches results in a 1D supermicellar chain in situ by minimizing the enthalpic penalty of exposing the growing chains to solvent. Its length grows with increasing degree of polymerization, confirming that the supramolecular polymerization was triggered and controlled by polymerization. Our results highlight the observation that (1) the entire self-assembly process of forming, compartmentalizing, and associating the micelles can be driven by polymerization in a concerted manner and that (2) polymerization-induced self-assembly now can use compartmentalized nanoobjects as substrates beyond block copolymer chains. Polymerization-induced supramolecular polymerization could be useful for the autonomous preparation of hierarchical nanostructures.

We report polymerization-induced self-assembly via controlled cross-linking copolymerization to produce robust block copolymer micelles with spherical, elongated, and branched shapes. Reversible addition–fragmentation chain transfer (RAFT) copolymerization of styrene and divinylbenzene (DVB) or 1,2-bismaleimidoethane (BMI) as a cross-linker in the presence of a polylactide macro-chain transfer agent (PLA-CTA) was performed in acetonitrile, which is a non-solvent to polystyrene (PS). The addition of the cross-linker accelerates the copolymerization compared to styrene homopolymerization, which leads to the formation of block polymer micelles within a shorter time frame, followed by in situ inter-chain cross-linking. The micelles are virtually identical to the core cross-linked star polymer consisting of a cross-linked polystyrenic core surrounded by a PLA corona. Molecular weights up to more than 1000 kg mol−1 could be obtained with relatively narrow dispersity values (1.1–1.4). In the case of copolymerization with DVB, the micellar morphology changes from spherical to elongated and branched shapes with increasing conversion. The size and morphology of the micelles are retained in a good solvent to PS, suggesting that the in situ cross-linking effectively stabilizes the micellar core. BMI undergoes alternating copolymerization with styrene in the early stage of polymerization and yields spherical micelles exclusively, because the densely cross-linked core seems to prevent further morphological transition.