We report growing a polymer chain from the backbone of a bottlebrush polymer in the neat polymerization condition produces nanostructured polymer monoliths with ordered morphologies based on the Janus bottlebrush architecture. We installed a norbornene unit at the end of the polylactide macro-chain transfer agent (PLA-CTA) by single unit monomer insertion. We polymerized the resulting macromonomer via ring-opening metathesis polymerization to produce the PLA bottlebrush polymer, where a trithiocarbonate moiety remains on the backbone per every repeating unit. Neat polymerization of styrene in the presence of the PLA bottlebrush polymer proceeded in a grafting-from manner following the reversible addition–fragmentation chain transfer mechanism, resulting in a monolithic solid containing the doubly grafted PLA and polystyrene (PS) side chains. Polymerization-induced microphase separation (PIMS) spontaneously occurred, driven by the incompatibility between PLA and the growing PS segment. In contrast to the significant disordered fraction in PLA-b-PS produced with the linear PLA-CTA, the PLA/PS Janus bottlebrush polymer showed improved order across the investigated composition range. Formation of the asymmetric lamellae up to >80 vol % of PS indicated a strong preference for the lamellar symmetry of the Janus architecture. The in situ structured monoliths even exhibited narrower scattering peak widths compared to the solution-cast and annealed sample, suggesting the utility of the Janus PIMS process for facile preparation of ordered nanostructured materials with uniform domain size.

Macromolecular self-assembly is essential in life and interfacial science. A macromolecule consisting of chemically distinct components tends to self-assemble in a selective solvent to minimize the exposure of the solvophobic segments to the medium while the solvophilic segments adopt extended conformations. While micelles composed of linear block copolymers represent classic examples of such solution assembly, recent interest focuses on the self-assembly of complex macromolecules with nonlinear architectures, such as star, graft, and bottlebrush. Such macromolecules include several to hundreds of polymer chains covalently tied to a core and a backbone. The pre-programmed, non-exchangeable chain arrangement makes a huge difference in their self-assembly. The field has witnessed tremendous advances in synthetic methodologies to construct the desired architectures, leading to discoveries of exotic self-assembly behavior. Thanks to the rapid evolution of computing power, computer simulation has also been an emerging and complementary approach for understanding the association mechanism and further predicting the self-assembling morphologies. However, simulating the self-assembly of architected macromolecules has posed a challenge as a huge number of objects should be included in the simulations. Comparing experimental results with simulations is not always straightforward, as synthetic routes to well-defined model systems with systematically controlled structural parameters are not often available. In this manuscript, we propose to bridge a gap between experiments and simulations in self-assembly of architected macromolecules. We focus on the key articles in this area reporting experimental evidence and simulation details and also cover recent examples in the literature. We start with discussing simulation methodologies applicable to investigate solution self-assembly across multiple levels of chemical resolution from all-atom to particle dynamics. Then, we delve into topological design, synthesis, and simulation of nonlinear macromolecules, including dendritic/star, network, and graft/bottlebrush polymers, to understand the architectural effect on the self-assembly behavior. We expand our discourse to embrace recent advances toward realizing more complex systems. For example, self-assembly in the presence of strong Coulombic interactions, such as in the case of polyelectrolytes, geometric constraints, and other components in solutions, exemplified by inorganic fillers, are introduced. Finally, the challenges and perspectives are discussed in the final section of the manuscript.

In this study, we present extensive dissipative particle dynamics simulation studies of bottlebrush copolymers in solution having different grafting sequences: block and random. Distinct morphology of the grafting sequence-controlled bottlebrush copolymer micelles is investigated through backbone chain distribution along with the micelle structure. As a result, bottlebrush block copolymer (BBCP) micelles exhibit backbone chain primarily dependent on length scale of micelle size, while bottlebrush random copolymer (BRCP) exhibits side chain-dependent length scale. We further quantify the dependence of the micelles on the length scale of the backbone chain and side chain using the scaling relationship. We decouple the size of the micelles into core radius and corona thickness, and scaling behavior of these structures is quantitatively explained by the conformation of backbone chains and side chains. Also, the experimental scaling of BBCP and BRCP micelles in water shows consistent results of the sequence-dependent scaling exponents calculated by simulation. This work reveals the scaling behavior of the sequence-controlled graft copolymer micelles which potentially guides how one can modify the solution self-assembled complex micelles by controlling architecture and structure parameters of the bottlebrush copolymer.

We report the synthesis and self-assembly of brush–linear diblock copolymers with variable side-chain length and density. Poly(pentafluorophenyl acrylate-g-ethylene glycol)-b-polystyrene ((PPFPA-g-PEG)-b-PS) brush–linear diblock copolymers are prepared by sequential reversible addition–fragmentation chain transfer (RAFT) polymerization of PPFPA and PS, followed by postpolymerization reaction between the precursor PPFPA-b-PS diblock copolymer and amine-functionalized PEG. By controlling the PEG chain length and the degree of substitution, we obtained brush–linear diblock copolymers with different side-chain lengths and densities. The solid-state morphologies of the diblocks are then examined by small-angle X-ray scattering (SAXS). At low PEG side-chain density, the segregation of PEG and PS away from PPFPA leads to the formation of PEG and PS lamellar domains with PPFPA in the interface. At high PEG side-chain density, the segregation is between the PPFPA-g-PEG brush block and the PS linear block, and the domain morphology is determined by the composition of the brush block. A partial experimental phase diagram is presented, and it illustrates the importance of both side-chain length and density on the microdomain morphology of brush–linear diblock copolymers.

Bottlebrush polymers (BBPs) are a type of comb-like macromolecule with densely grafted polymeric sidechains attached to the polymer backbones, and many intriguing properties and applications have been demonstrated due to their unique architecture. Moreover, a ring-opening metathesis polymerization (ROMP) technique using Grubbs catalysts allows a precise control of various structural parameters in BBPs, such as the sidechain length, backbone length, and sidechain microstructures. This review mainly highlights recent advances of BBPs prepared by ROMP, from synthesis efforts to properties and applications.

We report the self-assembly of monolayer vesicles from Janus core–shell bottlebrush polymers. A route was developed to synthesize doubly grafted bottlebrush copolymers (DGBCPs) possessing A-b-B and B′-b-C side chains on a single repeating unit. Graft-through ring-opening metathesis polymerization of a norbornene moiety installed by single unit monomer insertion allowed us to place the backbone on any repeating unit of the core (B and B′) block. By decorating each core chain end with different chains via reversible addition–fragmentation chain transfer polymerization, we can obtain nanoobjects with an asymmetric B core and a phase-separated A/C shell. We demonstrate that polystyrene-branch-polystyrene′ and polylactide-b-polystyrene-branch-polystyrene′-b-poly(n-butyl acrylate) macromonomers can be successfully synthesized and polymerized to produce DGBCPs in high yields (81–94% conversion) with an absolute molar mass of 149–395 kg mol–1 and a dispersity of 1.18–1.38. In a solvent slightly more selective to A than C, self-assembly of monolayer vesicles with diameter of <100 nm was observed by transmission electron microscopy. Dissipative particle dynamics simulations suggest that increasing the backbone length and moving the backbone toward the B′/C interface increases the backbone bending energy and favors a lower curvature. The spontaneous curvature appears to prefer a particular layer radius, avoiding bilayer formation.