In situ conversion from crew-cut to hairy micelles by surface-initiated polymerization

Whether spherical micelles of block copolymers have short or long coronas is intrinsically determined by the molecular weight of the corona-forming block with respect to that of the core block before the micelles are assembled. Because of the inherent conditions of packing copolymer chains into a micelle, the core diameter is altered when we assemble a micelle from a block copolymer having a long corona block, compared to that having a short corona block with the same length of the core block. However, micelles with the same core diameter but having various corona lengths can be guaranteed when the cor-ona is extended upon surface-initiated polymerization on the micelles. Herein, we demonstrated in situ conversion from crew-cut to hairy micelles by selectively extending a corona block while maintaining the spherical shape of block copolymer micelles. We first synthesized block copolymers having a chain trans-fer agent (CTA) positioned at the end of the corona block and then assembled them into a crew-cut micelle. Employing this micelle as an assembly of macro-CTAs, we conducted surface-initiated polymer-ization on the micelle by photo-induced energy/electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. Since PET-RAFT enables the polymerization at room temperature, the corona block was selectively extended with preservation of the core diameter, thereby converting a crew-cut micelle to a hairy one. In addition, by applying the same polymerization protocol to a worm-like micelle, we could selectively extend the coronas, leading to the formation of a worm-like micelle with a long corona. If such copolymer chains were assembled into a micelle, we would obtain a spherical micelle instead of a worm-like micelle having a hairy corona, which is difficult to assess because of the inherent packing problem. (c) 2021 Elsevier Inc. All rights reserved.

Automated summary

The length of the corona in spherical micelles of block copolymers is determined by the molecular weight of the corona-forming block relative to that of the core block before assembly. By selectively extending the corona block using surface-initiated polymerization, it is possible to convert crew-cut micelles to hairy micelles while maintaining the spherical shape. This method allows for the creation of micelles with different corona lengths and shapes, providing insight into the packing problem in copolymer micelle assembly.